Perform One-to-One Joins执行一对一连接

Create the Template App创建模板应用程序

Before you begin following this aggregation tutorial, you must set up a new C app. You can use this app to connect to a MongoDB deployment, insert sample data into MongoDB, and run the aggregation pipeline.在开始学习此聚合教程之前，您必须设置一个新的C应用程序。您可以使用此应用程序连接到MongoDB部署，将示例数据插入MongoDB，并运行聚合管道。

After you install the driver, create a file called agg-tutorial.c. Paste the following code in this file to create an app template for the aggregation tutorials.安装驱动程序后，创建一个名为agg-tutorialc的文件。将以下代码粘贴到此文件中，为聚合教程创建应用程序模板。

#include <stdio.h>
#include <bson/bson.h>
#include <mongoc/mongoc.h>

int main(void)
{
    mongoc_init();

    // Replace the placeholder with your connection string.
    char *uri = "<connection string>";
    mongoc_client_t* client = mongoc_client_new(uri);

    // Get a reference to relevant collections.
    // ... mongoc_collection_t *some_coll = mongoc_client_get_collection(client, "agg_tutorials_db", "some_coll");
    // ... mongoc_collection_t *another_coll = mongoc_client_get_collection(client, "agg_tutorials_db", "another_coll");

    // Delete any existing documents in collections if needed.
    // ... {
    // ...     bson_t *filter = bson_new();
    // ...     bson_error_t error;
    // ...     if (!mongoc_collection_delete_many(some_coll, filter, NULL, NULL, &error))
    // ...     {
    // ...         fprintf(stderr, "Delete error: %s\n", error.message);
    // ...     }
    // ...     bson_destroy(filter);
    // ... }

    // Insert sample data into the collection or collections.
    // ... {
    // ...     size_t num_docs = ...;
    // ...     bson_t *docs[num_docs];
    // ...
    // ...     docs[0] = ...;
    // ...
    // ...     bson_error_t error;
    // ...     if (!mongoc_collection_insert_many(some_coll, (const bson_t **)docs, num_docs, NULL, NULL, &error))
    // ...     {
    // ...         fprintf(stderr, "Insert error: %s\n", error.message);
    // ...     }
    // ...
    // ...     for (int i = 0; i < num_docs; i++)
    // ...     {
    // ...         bson_destroy(docs[i]);
    // ...     }
    // ... }

    {
        const bson_t *doc;

        // Add code to create pipeline stages.
        bson_t *pipeline = BCON_NEW("pipeline", "[",
        // ... Add pipeline stages here.
        "]");

        // Run the aggregation.
        // ... mongoc_cursor_t *results = mongoc_collection_aggregate(some_coll, MONGOC_QUERY_NONE, pipeline, NULL, NULL);

        bson_destroy(pipeline);

        // Print the aggregation results.
        while (mongoc_cursor_next(results, &doc))
        {
            char *str = bson_as_canonical_extended_json(doc, NULL);
            printf("%s\n", str);
            bson_free(str);
        }
        bson_error_t error;
        if (mongoc_cursor_error(results, &error))
        {
            fprintf(stderr, "Aggregation error: %s\n", error.message);
        }

        mongoc_cursor_destroy(results);
    }

    // Clean up resources.
    // ... mongoc_collection_destroy(some_coll);
    mongoc_client_destroy(client);
    mongoc_cleanup();

    return EXIT_SUCCESS;
}

For every tutorial, you must replace the connection string placeholder with your deployment's connection string.对于每个教程，您必须将连接字符串占位符替换为部署的连接字符串。

For example, if your connection string is "mongodb+srv://mongodb-example:27017", your connection string assignment resembles the following:例如，如果连接字符串是"mongodb+srv://mongodb-example:27017"，连接字符串分配类似于以下内容：

char *uri = "mongodb+srv://mongodb-example:27017";

Create the Collection创建集合

This example uses two collections:此示例使用两个集合：

• orders: documents that describe individual orders for products in a shop：描述商店中单个产品订单的文档
• products: documents that describe the products that a shop sells：描述商店销售产品的文档

An order can only contain one product. The aggregation uses a one-to-one join to match an order document to the corresponding product document. The aggregation joins the collections by the product_id field that exists in documents in both collections.一个订单只能包含一个产品。聚合使用一对一连接将订单文档与相应的产品文档相匹配。聚合通过两个集合中文档中存在的product_id字段将集合连接起来。

To create the orders and products collections and insert the sample data, add the following code to your application:要创建orders和products集合并插入示例数据，请将以下代码添加到应用程序中：

mongoc_collection_t *orders = mongoc_client_get_collection(client, "agg_tutorials_db", "orders");
mongoc_collection_t *products = mongoc_client_get_collection(client, "agg_tutorials_db", "products");

{
    bson_t *filter = bson_new();
    bson_error_t error;
    if (!mongoc_collection_delete_many(orders, filter, NULL, NULL, &error))
    {
        fprintf(stderr, "Delete error: %s\n", error.message);
    }
    if (!mongoc_collection_delete_many(products, filter, NULL, NULL, &error))
    {
        fprintf(stderr, "Delete error: %s\n", error.message);
    }
    bson_destroy(filter);
}

{
    size_t num_docs = 4;
    bson_t *order_docs[num_docs];

    order_docs[0] = BCON_NEW(
        "customer_id", BCON_UTF8("elise_smith@myemail.com"),
        "orderdate", BCON_DATE_TIME(1590822952000UL), // 2020-05-30T08:35:52Z
        "product_id", BCON_UTF8("a1b2c3d4"),
        "value", BCON_DOUBLE(431.43));

    order_docs[1] = BCON_NEW(
        "customer_id", BCON_UTF8("tj@wheresmyemail.com"),
        "orderdate", BCON_DATE_TIME(1559063612000UL), // 2019-05-28T19:13:32Z
        "product_id", BCON_UTF8("z9y8x7w6"),
        "value", BCON_DOUBLE(5.01));

    order_docs[2] = BCON_NEW(
        "customer_id", BCON_UTF8("oranieri@warmmail.com"),
        "orderdate", BCON_DATE_TIME(1577869537000UL), // 2020-01-01T08:25:37Z
        "product_id", BCON_UTF8("ff11gg22hh33"),
        "value", BCON_DOUBLE(63.13));

    order_docs[3] = BCON_NEW(
        "customer_id", BCON_UTF8("jjones@tepidmail.com"),
        "orderdate", BCON_DATE_TIME(1608976546000UL), // 2020-12-26T08:55:46Z
        "product_id", BCON_UTF8("a1b2c3d4"),
        "value", BCON_DOUBLE(429.65));

    bson_error_t error;
    if (!mongoc_collection_insert_many(orders, (const bson_t **)order_docs, num_docs, NULL, NULL, &error))
    {
        fprintf(stderr, "Insert error: %s\n", error.message);
    }

    for (int i = 0; i < num_docs; i++)
    {
        bson_destroy(order_docs[i]);
    }
}

{
    size_t num_docs = 4;
    bson_t *product_docs[num_docs];

    product_docs[0] = BCON_NEW(
        "id", BCON_UTF8("a1b2c3d4"),
        "name", BCON_UTF8("Asus Laptop"),
        "category", BCON_UTF8("ELECTRONICS"),
        "description", BCON_UTF8("Good value laptop for students"));

    product_docs[1] = BCON_NEW(
        "id", BCON_UTF8("z9y8x7w6"),
        "name", BCON_UTF8("The Day Of The Triffids"),
        "category", BCON_UTF8("BOOKS"),
        "description", BCON_UTF8("Classic post-apocalyptic novel"));

    product_docs[2] = BCON_NEW(
        "id", BCON_UTF8("ff11gg22hh33"),
        "name", BCON_UTF8("Morphy Richardds Food Mixer"),
        "category", BCON_UTF8("KITCHENWARE"),
        "description", BCON_UTF8("Luxury mixer turning good cakes into great"));

    product_docs[3] = BCON_NEW(
        "id", BCON_UTF8("pqr678st"),
        "name", BCON_UTF8("Karcher Hose Set"),
        "category", BCON_UTF8("GARDEN"),
        "description", BCON_UTF8("Hose + nozzles + winder for tidy storage"));

    bson_error_t error;
    if (!mongoc_collection_insert_many(products, (const bson_t **)product_docs, num_docs, NULL, NULL, &error))
    {
        fprintf(stderr, "Insert error: %s\n", error.message);
    }

    for (int i = 0; i < num_docs; i++)
    {
        bson_destroy(product_docs[i]);
    }
}

Create the Template App创建模板应用程序

Before you begin following an aggregation tutorial, you must set up a new C++ app. You can use this app to connect to a MongoDB deployment, insert sample data into MongoDB, and run the aggregation pipeline.在开始学习聚合教程之前，您必须设置一个新的C++应用程序。您可以使用此应用程序连接到MongoDB部署，将示例数据插入MongoDB，并运行聚合管道。

After you install the driver, create a file called agg-tutorial.cpp. Paste the following code in this file to create an app template for the aggregation tutorials.安装驱动程序后，创建一个名为agg-tutorial.cpp的文件。将以下代码粘贴到此文件中，为聚合教程创建应用程序模板。

#include <iostream>
#include <bsoncxx/builder/basic/document.hpp>
#include <bsoncxx/builder/basic/kvp.hpp>
#include <bsoncxx/json.hpp>
#include <mongocxx/client.hpp>
#include <mongocxx/instance.hpp>
#include <mongocxx/pipeline.hpp>
#include <mongocxx/uri.hpp>
#include <chrono>

using bsoncxx::builder::basic::kvp;
using bsoncxx::builder::basic::make_document;
using bsoncxx::builder::basic::make_array;

int main() {
   mongocxx::instance instance;

   // Replace the placeholder with your connection string.
   mongocxx::uri uri("<connection string>");
   mongocxx::client client(uri);

   auto db = client["agg_tutorials_db"];
   // Delete existing data in the database, if necessary.
   db.drop();

   // Get a reference to relevant collections.
   // ... auto some_coll = db["..."];
   // ... auto another_coll = db["..."];

   // Insert sample data into the collection or collections.
   // ... some_coll.insert_many(docs);

   // Create an empty pipelne.
   mongocxx::pipeline pipeline;

   // Add code to create pipeline stages.
   // pipeline.match(make_document(...));

   // Run the aggregation and print the results.
   auto cursor = orders.aggregate(pipeline);
   for (auto&& doc : cursor) {
      std::cout << bsoncxx::to_json(doc, bsoncxx::ExtendedJsonMode::k_relaxed) << std::endl;
   }
}

For every tutorial, you must replace the connection string placeholder with your deployment's connection string.对于每个教程，您必须将连接字符串占位符替换为部署的连接字符串。

For example, if your connection string is "mongodb+srv://mongodb-example:27017", your connection string assignment resembles the following:例如，如果连接字符串是"mongodb+srv://mongodb-example:27017"，连接字符串分配类似于以下内容：

mongocxx::uri uri{"mongodb+srv://mongodb-example:27017"};

Create the Collection创建集合

This example uses two collections:此示例使用两个集合：

• orders: documents that describe individual orders for products in a shop：描述商店中单个产品订单的文档
• products: documents that describe the products that a shop sells：描述商店销售产品的文档

An order can only contain one product. The aggregation uses a one-to-one join to match an order document to the corresponding product document. The aggregation joins the collections by the product_id field that exists in documents in both collections.一个订单只能包含一个产品。聚合使用一对一连接将订单文档与相应的产品文档相匹配。聚合通过两个集合中文档中存在的product_id字段将集合连接起来。

To create the orders and products collections and insert the sample data, add the following code to your application:要创建orders和products集合并插入示例数据，请将以下代码添加到应用程序中：

auto orders = db["orders"];
auto products = db["products"];

std::vector<bsoncxx::document::value> order_docs = {bsoncxx::from_json(R"({
          "customer_id": "elise_smith@myemail.com",
          "orderdate": {"$date": 1590821752000},
          "product_id": "a1b2c3d4",
          "value": 431.43
      })"),
                                                    bsoncxx::from_json(R"({
          "customer_id": "tj@wheresmyemail.com",
          "orderdate": {"$date": 1559062412},
          "product_id": "z9y8x7w6",
          "value": 5.01
      })"),
                                                    bsoncxx::from_json(R"({
          "customer_id": "oranieri@warmmail.com",
          "orderdate": {"$date": 1577861137},
          "product_id": "ff11gg22hh33",
          "value": 63.13
      })"),
                                                    bsoncxx::from_json(R"({
          "customer_id": "jjones@tepidmail.com",
          "orderdate": {"$date": 1608972946000},
          "product_id": "a1b2c3d4",
          "value": 429.65
      })")};

orders.insert_many(order_docs);  // Might throw an exception

std::vector<bsoncxx::document::value> product_docs = {bsoncxx::from_json(R"({
          "id": "a1b2c3d4",
          "name": "Asus Laptop",
          "category": "ELECTRONICS",
          "description": "Good value laptop for students"
      })"),
                                                      bsoncxx::from_json(R"({
          "id": "z9y8x7w6",
          "name": "The Day Of The Triffids",
          "category": "BOOKS",
          "description": "Classic post-apocalyptic novel"
      })"),
                                                      bsoncxx::from_json(R"({
          "id": "ff11gg22hh33",
          "name": "Morphy Richardds Food Mixer",
          "category": "KITCHENWARE",
          "description": "Luxury mixer turning good cakes into great"
      })"),
                                                      bsoncxx::from_json(R"({
          "id": "pqr678st",
          "name": "Karcher Hose Set",
          "category": "GARDEN",
          "description": "Hose + nozzles + winder for tidy storage"
      })")};

products.insert_many(product_docs);  // Might throw an exception

Create the Template App创建模板应用程序

Before you begin following this aggregation tutorial, you must set up a new C#/.NET app. You can use this app to connect to a MongoDB deployment, insert sample data into MongoDB, and run the aggregation pipeline.在开始学习此聚合教程之前，您必须设置一个新的C#/NET应用程序。您可以使用此应用程序连接到MongoDB部署，将示例数据插入MongoDB，并运行聚合管道。

After you install the driver, paste the following code into your Program.cs file to create an app template for the aggregation tutorials.安装驱动程序后，将以下代码粘贴到Program.cs文件中，为聚合教程创建应用程序模板。

using MongoDB.Bson;
using MongoDB.Bson.Serialization.Attributes;
using MongoDB.Driver;

// Define data model classes.
// ... public class MyClass { ... }

// Replace the placeholder with your connection string.
var uri = "<connection string>";
var client = new MongoClient(uri);
var aggDB = client.GetDatabase("agg_tutorials_db");

// Get a reference to relevant collections.
// ... var someColl = aggDB.GetCollection<MyClass>("someColl");
// ... var anotherColl = aggDB.GetCollection<MyClass>("anotherColl");

// Delete any existing documents in collections if needed.
// ... someColl.DeleteMany(Builders<MyClass>.Filter.Empty);

// Insert sample data into the collection or collections.
// ... someColl.InsertMany(new List<MyClass> { ... });

// Add code to chain pipeline stages to the Aggregate() method.
// ... var results = someColl.Aggregate().Match(...);

// Print the aggregation results.
foreach (var result in results.ToList())
{
    Console.WriteLine(result);
}

For every tutorial, you must replace the connection string placeholder with your deployment's connection string.对于每个教程，您必须将连接字符串占位符替换为部署的连接字符串。

For example, if your connection string is "mongodb+srv://mongodb-example:27017", your connection string assignment resembles the following:例如，如果连接字符串是"mongodb+srv://mongodb-example:27017"，连接字符串分配类似于以下内容：

var uri = "mongodb+srv://mongodb-example:27017";

Create the Collection创建集合

This example uses two collections:此示例使用两个集合：

• orders: documents that describe individual orders for products in a shop：描述商店中单个产品订单的文档
• products: documents that describe the products that a shop sells：描述商店销售产品的文档

An order must contain one product. The aggregation uses a one-to-one join to match an order document to the corresponding product document. The aggregation joins the collections by the ProductId field that exists in documents in both collections.订单必须包含一个产品。聚合使用一对一连接将订单文档与相应的产品文档相匹配。聚合通过两个集合中文档中存在的ProductId字段将集合连接起来。

First, create C# classes to model the data in the orders and products collections:首先，创建C#类来对orders和products集合中的数据进行建模：

public class Order
{
    [BsonId]
    public ObjectId Id { get; set; }
    public required string CustomerId { get; set; }
    public DateTime OrderDate { get; set; }
    public required string ProductId { get; set; }
    public double Value { get; set; }
}

public class Product
{
    [BsonId]
    public required string Id { get; set; }

    public string Name { get; set; } = "";
    public string Category { get; set; } = "";
    public string Description { get; set; } = "";
}

To create the orders and products collections and insert the sample data, add the following code to your application:要创建orders和products集合并插入示例数据，请将以下代码添加到应用程序中：

var orders = aggDB.GetCollection<Order>("orders");
var products = aggDB.GetCollection<Product>("products");

orders = aggDB.GetCollection<Order>("orders");
products = aggDB.GetCollection<Product>("products");

orders.InsertMany(new List<Order>
{
    new Order
    {
        CustomerId = "elise_smith@myemail.com",
        OrderDate = DateTime.Parse("2020-05-30T08:35:52Z"),
        ProductId = "a1b2c3d4",
        Value = 431.43
    },
    new Order
    {
        CustomerId = "tj@wheresmyemail.com",
        OrderDate = DateTime.Parse("2019-05-28T19:13:32Z"),
        ProductId = "z9y8x7w6",
        Value = 5.01
    },
    new Order
    {
        CustomerId = "oranieri@warmmail.com",
        OrderDate = DateTime.Parse("2020-01-01T08:25:37Z"),
        ProductId = "ff11gg22hh33",
        Value = 63.13
    },
    new Order
    {
        CustomerId = "jjones@tepidmail.com",
        OrderDate = DateTime.Parse("2020-12-26T08:55:46Z"),
        ProductId = "a1b2c3d4",
        Value = 429.65
    }
});

products.InsertMany(new List<Product>
{
    new Product
    {
        Id = "a1b2c3d4",
        Name = "Asus Laptop",
        Category = "ELECTRONICS",
        Description = "Good value laptop for students"
    },
    new Product
    {
        Id = "z9y8x7w6",
        Name = "The Day Of The Triffids",
        Category = "BOOKS",
        Description = "Classic post-apocalyptic novel"
    },
    new Product
    {
        Id = "ff11gg22hh33",
        Name = "Morphy Richardds Food Mixer",
        Category = "KITCHENWARE",
        Description = "Luxury mixer turning good cakes into great"
    },
    new Product
    {
        Id = "pqr678st",
        Name = "Karcher Hose Set",
        Category = "GARDEN",
        Description = "Hose + nozzles + winder for tidy storage"
    }
});

Create the Template App创建模板应用程序

Before you begin following this aggregation tutorial, you must set up a new Go app. You can use this app to connect to a MongoDB deployment, insert sample data into MongoDB, and run the aggregation pipeline.在开始学习此聚合教程之前，您必须设置一个新的Go应用程序。您可以使用此应用程序连接到MongoDB部署，将示例数据插入MongoDB，并运行聚合管道。

After you install the driver, create a file called agg_tutorial.go. Paste the following code in this file to create an app template for the aggregation tutorials.安装驱动程序后，创建一个名为agg_tutorial.go的文件。将以下代码粘贴到此文件中，为聚合教程创建应用程序模板。

package main

import (
	"context"
	"fmt"
	"log"

	"go.mongodb.org/mongo-driver/v2/bson"
	"go.mongodb.org/mongo-driver/v2/mongo"
	"go.mongodb.org/mongo-driver/v2/mongo/options"
)

// Define structs.
// type MyStruct struct { ... }

func main() {
	ctx := context.Background()
	// Replace the placeholder with your connection string.
	const uri = "<connection string>"

	client, err := mongo.Connect(options.Client().ApplyURI(uri))
	if err != nil {
		log.Fatal(err)
	}

	defer func() {
		if err = client.Disconnect(ctx); err != nil {
			log.Fatal(err)
		}
	}()

	aggDB := client.Database("agg_tutorials_db")

	// Get a reference to relevant collections.
	// ... someColl := aggDB.Collection("...")
	// ... anotherColl := aggDB.Collection("...")

	// Delete any existing documents in collections if needed.
	// ... someColl.DeleteMany(cxt, bson.D{})

	// Insert sample data into the collection or collections.
	// ... _, err = someColl.InsertMany(...)

	// Add code to create pipeline stages.
	// ... myStage := bson.D{{...}}

	// Create a pipeline that includes the stages.
	// ... pipeline := mongo.Pipeline{...}

	// Run the aggregation.
	// ... cursor, err := someColl.Aggregate(ctx, pipeline)

	if err != nil {
		log.Fatal(err)
	}

	defer func() {
		if err := cursor.Close(ctx); err != nil {
			log.Fatalf("failed to close cursor: %v", err)
		}
	}()

	// Decode the aggregation results.
	var results []bson.D
	if err = cursor.All(ctx, &results); err != nil {
		log.Fatalf("failed to decode results: %v", err)
	}

	// Print the aggregation results.
	for _, result := range results {
		res, _ := bson.MarshalExtJSON(result, false, false)
		fmt.Println(string(res))
	}
}

For every tutorial, you must replace the connection string placeholder with your deployment's connection string.对于每个教程，您必须将连接字符串占位符替换为部署的连接字符串。

For example, if your connection string is "mongodb+srv://mongodb-example:27017", your connection string assignment resembles the following:例如，如果连接字符串是"mongodb+srv://mongodb-example:27017"，连接字符串分配类似于以下内容：

const uri = "mongodb+srv://mongodb-example:27017";

Create the Collection创建集合

This example uses two collections:此示例使用两个集合：

• orders: documents that describe individual orders for products in a shop：描述商店中单个产品订单的文档
• products: documents that describe the products that a shop sells：描述商店销售产品的文档

An order can only contain one product. The aggregation uses a one-to-one join to match an order document to the corresponding product document. The aggregation joins the collections by the product_id field that exists in documents in both collections.一个订单只能包含一个产品。聚合使用一对一连接将订单文档与相应的产品文档相匹配。聚合通过两个集合中文档中存在的product_id字段将集合连接起来。

First, create Go structs to model the data in the orders and products collections:首先，创建Go结构体来对orders和products集合中的数据进行建模：

type Order struct {
	CustomerID string        `bson:"customer_id"`
	OrderDate  bson.DateTime `bson:"orderdate"`
	ProductID  string        `bson:"product_id"`
	Value      float32       `bson:"value"`
}

type Product struct {
	ID          string `bson:"id"`
	Name        string `bson:"name"`
	Category    string `bson:"category"`
	Description string `bson:"description"`
}

To create the orders and products collections and insert the sample data, add the following code to your application:要创建orders和products集合并插入示例数据，请将以下代码添加到应用程序中：

orders := aggDB.Collection("orders")
products := aggDB.Collection("products")

_, err = orders.InsertMany(ctx, []interface{}{
	Order{
		CustomerID: "elise_smith@myemail.com",
		OrderDate:  bson.NewDateTimeFromTime(time.Date(2020, 5, 30, 8, 35, 52, 0, time.UTC)),
		ProductID:  "a1b2c3d4",
		Value:      431.43,
	},
	Order{
		CustomerID: "tj@wheresmyemail.com",
		OrderDate:  bson.NewDateTimeFromTime(time.Date(2019, 5, 28, 19, 13, 32, 0, time.UTC)),
		ProductID:  "z9y8x7w6",
		Value:      5.01,
	},
	Order{
		CustomerID: "oranieri@warmmail.com",
		OrderDate:  bson.NewDateTimeFromTime(time.Date(2020, 01, 01, 8, 25, 37, 0, time.UTC)),
		ProductID:  "ff11gg22hh33",
		Value:      63.13,
	},
	Order{
		CustomerID: "jjones@tepidmail.com",
		OrderDate:  bson.NewDateTimeFromTime(time.Date(2020, 12, 26, 8, 55, 46, 0, time.UTC)),
		ProductID:  "a1b2c3d4",
		Value:      429.65,
	},
})
if err != nil {

	log.Fatal(err)
}

_, err = products.InsertMany(ctx, []interface{}{
	Product{
		ID:          "a1b2c3d4",
		Name:        "Asus Laptop",
		Category:    "ELECTRONICS",
		Description: "Good value laptop for students",
	},
	Product{
		ID:          "z9y8x7w6",
		Name:        "The Day Of The Triffids",
		Category:    "BOOKS",
		Description: "Classic post-apocalyptic novel",
	},
	Product{
		ID:          "ff11gg22hh33",
		Name:        "Morphy Richardds Food Mixer",
		Category:    "KITCHENWARE",
		Description: "Luxury mixer turning good cakes into great",
	},
	Product{
		ID:          "pqr678st",
		Name:        "Karcher Hose Set",
		Category:    "GARDEN",
		Description: "Hose + nozzles + winder for tidy storage",
	},
})
if err != nil {
	log.Fatal(err)
}

Create the Template App创建模板应用程序

Before you begin following an aggregation tutorial, you must set up a new Java app. You can use this app to connect to a MongoDB deployment, insert sample data into MongoDB, and run the aggregation pipeline.在开始学习聚合教程之前，您必须设置一个新的Java应用程序。您可以使用此应用程序连接到MongoDB部署，将示例数据插入MongoDB，并运行聚合管道。

After you install the driver, create a file called AggTutorial.java. Paste the following code in this file to create an app template for the aggregation tutorials.安装驱动程序后，创建一个名为AggTutorial.java的文件。将以下代码粘贴到此文件中，为聚合教程创建应用程序模板。

package org.example;

// Modify imports for each tutorial as needed.
import com.mongodb.client.*;
import com.mongodb.client.model.Accumulators;
import com.mongodb.client.model.Aggregates;
import com.mongodb.client.model.Field;
import com.mongodb.client.model.Filters;
import com.mongodb.client.model.Sorts;
import com.mongodb.client.model.Variable;
import org.bson.Document;
import org.bson.conversions.Bson;

import java.time.LocalDateTime;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

public class AggTutorial {
    public static void main(String[] args) {
        // Replace the placeholder with your connection string.
        String uri = "<connection string>";

        try (MongoClient mongoClient = MongoClients.create(uri)) {
            MongoDatabase aggDB = mongoClient.getDatabase("agg_tutorials_db");

            // Get a reference to relevant collections.
            // ... MongoCollection<Document> someColl = ...
            // ... MongoCollection<Document> anotherColl = ...

            // Insert sample data into the collection or collections.
            // ... someColl.insertMany(...);

            // Create an empty pipeline array.
            List<Bson> pipeline = new ArrayList<>();

            // Add code to create pipeline stages.
            // ... pipeline.add(...);

            // Run the aggregation.
            // ... AggregateIterable<Document> aggregationResult =
            // someColl.aggregate(pipeline);

            // Print the aggregation results.
            for (Document document : aggregationResult) {
                System.out.println(document.toJson());
            }
        }
    }
}

For every tutorial, you must replace the connection string placeholder with your deployment's connection string.对于每个教程，您必须将连接字符串占位符替换为部署的连接字符串。

For example, if your connection string is "mongodb+srv://mongodb-example:27017", your connection string assignment resembles the following:例如，如果连接字符串是"mongodb+srv://mongodb-example:27017"，连接字符串分配类似于以下内容：

String uri = "mongodb+srv://mongodb-example:27017";

Create the Collection创建集合

This example uses two collections:此示例使用两个集合：

• orders: documents that describe individual orders for products in a shop：描述商店中单个产品订单的文档
• products: documents that describe the products that a shop sells：描述商店销售产品的文档

An order can only contain one product. The aggregation uses a one-to-one join to match an order document to the corresponding product document. The aggregation joins the collections by the product_id field that exists in documents in both collections.一个订单只能包含一个产品。聚合使用一对一连接将订单文档与相应的产品文档相匹配。聚合通过两个集合中文档中存在的product_id字段将集合连接起来。

To create the orders and products collections and insert the sample data, add the following code to your application:要创建orders和products集合并插入示例数据，请将以下代码添加到应用程序中：

MongoDatabase aggDB = mongoClient.getDatabase("agg_tutorials_db");
MongoCollection<Document> orders = aggDB.getCollection("orders");
MongoCollection<Document> products = aggDB.getCollection("products");

orders.insertMany(
        Arrays.asList(
                new Document("customer_id", "elise_smith@myemail.com")
                        .append("orderdate", LocalDateTime.parse("2020-05-30T08:35:52"))
                        .append("product_id", "a1b2c3d4")
                        .append("value", 431.43),
                new Document("customer_id", "tj@wheresmyemail.com")
                        .append("orderdate", LocalDateTime.parse("2019-05-28T19:13:32"))
                        .append("product_id", "z9y8x7w6")
                        .append("value", 5.01),
                new Document("customer_id", "oranieri@warmmail.com")
                        .append("orderdate", LocalDateTime.parse("2020-01-01T08:25:37"))
                        .append("product_id", "ff11gg22hh33")
                        .append("value", 63.13),
                new Document("customer_id", "jjones@tepidmail.com")
                        .append("orderdate", LocalDateTime.parse("2020-12-26T08:55:46"))
                        .append("product_id", "a1b2c3d4")
                        .append("value", 429.65)
        )
);

products.insertMany(
        Arrays.asList(
                new Document("id", "a1b2c3d4")
                        .append("name", "Asus Laptop")
                        .append("category", "ELECTRONICS")
                        .append("description", "Good value laptop for students"),
                new Document("id", "z9y8x7w6")
                        .append("name", "The Day Of The Triffids")
                        .append("category", "BOOKS")
                        .append("description", "Classic post-apocalyptic novel"),
                new Document("id", "ff11gg22hh33")
                        .append("name", "Morphy Richardds Food Mixer")
                        .append("category", "KITCHENWARE")
                        .append("description", "Luxury mixer turning good cakes into great"),
                new Document("id", "pqr678st")
                        .append("name", "Karcher Hose Set")
                        .append("category", "GARDEN")
                        .append("description", "Hose + nozzles + winder for tidy storage")
        )
);

Create the Template App创建模板应用程序

Before you begin following an aggregation tutorial, you must set up a new Kotlin app. You can use this app to connect to a MongoDB deployment, insert sample data into MongoDB, and run the aggregation pipeline.在开始学习聚合教程之前，您必须设置一个新的Kotlin应用程序。您可以使用此应用程序连接到MongoDB部署，将示例数据插入MongoDB，并运行聚合管道。

In addition to the driver, you must also add the following dependencies to your build.gradle.kts file and reload your project:除了驱动程序，您还必须将以下依赖项添加到build.gradle.kts文件中并重新加载项目：

dependencies {
    // Implements Kotlin serialization
    implementation("org.jetbrains.kotlinx:kotlinx-serialization-core:1.5.1")
    // Implements Kotlin date and time handling
    implementation("org.jetbrains.kotlinx:kotlinx-datetime:0.6.1")
}

After you install the driver, create a file called AggTutorial.kt. Paste the following code in this file to create an app template for the aggregation tutorials.安装驱动程序后，创建一个名为AggTutorial.kt的文件。将以下代码粘贴到此文件中，为聚合教程创建应用程序模板。

package org.example

// Modify imports for each tutorial as needed.
import com.mongodb.client.model.*
import com.mongodb.kotlin.client.coroutine.MongoClient
import kotlinx.coroutines.runBlocking
import kotlinx.datetime.LocalDateTime
import kotlinx.datetime.toJavaLocalDateTime
import kotlinx.serialization.Contextual
import kotlinx.serialization.Serializable
import org.bson.Document
import org.bson.conversions.Bson

// Define data classes.
@Serializable
data class MyClass(
    ...
)

suspend fun main() {
    // Replace the placeholder with your connection string.
    val uri = "<connection string>"

    MongoClient.create(uri).use { mongoClient ->
        val aggDB = mongoClient.getDatabase("agg_tutorials_db")

        // Get a reference to relevant collections.
        // ... val someColl = ...

        // Delete any existing documents in collections if needed.
        // ... someColl.deleteMany(empty())

        // Insert sample data into the collection or collections.
        // ... someColl.insertMany( ... )

        // Create an empty pipeline.
        val pipeline = mutableListOf<Bson>()

        // Add code to create pipeline stages.
        // ... pipeline.add(...)

        // Run the aggregation.
        // ... val aggregationResult = someColl.aggregate<Document>(pipeline)

        // Print the aggregation results.
        aggregationResult.collect { println(it) }
    }
}

For every tutorial, you must replace the connection string placeholder with your deployment's connection string.对于每个教程，您必须将连接字符串占位符替换为部署的连接字符串。

For example, if your connection string is "mongodb+srv://mongodb-example:27017", your connection string assignment resembles the following:例如，如果连接字符串是"mongodb+srv://mongodb-example:27017"，连接字符串分配类似于以下内容：

val uri = "mongodb+srv://mongodb-example:27017"

Create the Collection创建集合

This example uses two collections:此示例使用两个集合：

• orders: documents that describe individual orders for products in a shop：描述商店中单个产品订单的文档
• products: documents that describe the products that a shop sells：描述商店销售产品的文档

An order can only contain one product. The aggregation uses a one-to-one join to match an order document to the corresponding product document. The aggregation joins the collections by the product_id field that exists in documents in both collections.一个订单只能包含一个产品。聚合使用一对一连接将订单文档与相应的产品文档相匹配。聚合通过两个集合中文档中存在的product_id字段将集合连接起来。

First, create Kotlin data classes to model the data in the orders and products collections:首先，创建Kotlin数据类来对orders和products集合中的数据进行建模：

@Serializable
data class Order(
    val customerID: String,
    @Contextual val orderDate: LocalDateTime,
    val productID: String,
    val value: Double
)

@Serializable
data class Product(
    val ID: String,
    val name: String,
    val category: String,
    val description: String
)

To create the orders and products collections and insert the sample data, add the following code to your application:要创建orders和products集合并插入示例数据，请将以下代码添加到应用程序中：

val orders = aggDB.getCollection<Order>("orders")
val products = aggDB.getCollection<Product>("products")

orders.deleteMany(Filters.empty());
products.deleteMany(Filters.empty());

orders.insertMany(
    listOf(
        Order("elise_smith@myemail.com", LocalDateTime.parse("2020-05-30T08:35:52"), "a1b2c3d4", 431.43),
        Order("tj@wheresmyemail.com", LocalDateTime.parse("2019-05-28T19:13:32"), "z9y8x7w6", 5.01),
        Order("oranieri@warmmail.com", LocalDateTime.parse("2020-01-01T08:25:37"), "ff11gg22hh33", 63.13),
        Order("jjones@tepidmail.com", LocalDateTime.parse("2020-12-26T08:55:46"), "a1b2c3d4", 429.65)
    )
)

products.insertMany(
    listOf(
        Product("a1b2c3d4", "Asus Laptop", "ELECTRONICS", "Good value laptop for students"),
        Product("z9y8x7w6", "The Day Of The Triffids", "BOOKS", "Classic post-apocalyptic novel"),
        Product(
            "ff11gg22hh33",
            "Morphy Richardds Food Mixer",
            "KITCHENWARE",
            "Luxury mixer turning good cakes into great"
        ),
        Product("pqr678st", "Karcher Hose Set", "GARDEN", "Hose + nozzles + winder for tidy storage")
    )
)

Create the Template App创建模板应用程序

Before you begin following this aggregation tutorial, you must set up a new Node.js app. You can use this app to connect to a MongoDB deployment, insert sample data into MongoDB, and run the aggregation pipeline.在开始学习本聚合教程之前，您必须设置一个新的Node.js应用程序。您可以使用此应用程序连接到MongoDB部署，将示例数据插入MongoDB，并运行聚合管道。

After you install the driver, create a file to run the tutorial template. Paste the following code in this file to create an app template for the aggregation tutorials.安装驱动程序后，创建一个文件来运行教程模板。将以下代码粘贴到此文件中，为聚合教程创建应用程序模板。

const { MongoClient } = require('mongodb');
// Replace the placeholder with your connection string.
const uri = '<connection-string>';
const client = new MongoClient(uri);
export async function run() {
  try {
    const aggDB = client.db('agg_tutorials_db');

    // Get a reference to relevant collections.
    // ... const someColl =
    // ... const anotherColl =

    // Delete any existing documents in collections.
    // ... await someColl.deleteMany({});

    // Insert sample data into the collection or collections.
    // ... const someData = [ ... ];
    // ... await someColl.insertMany(someData);

    // Create an empty pipeline array.
    const pipeline = [];

    // Add code to create pipeline stages.
    // ... pipeline.push({ ... })

    // Run the aggregation.
    // ... const aggregationResult = ...

    // Print the aggregation results.
    for await (const document of aggregationResult) {
      console.log(document);
    }
  } finally {
    await client.close();
  }
}

run().catch(console.dir);

For every tutorial, you must replace the connection string placeholder with your deployment's connection string.对于每个教程，您必须将连接字符串占位符替换为部署的连接字符串。

For example, if your connection string is "mongodb+srv://mongodb-example:27017", your connection string assignment resembles the following:例如，如果连接字符串是"mongodb+srv://mongodb-example:27017"，连接字符串分配类似于以下内容：

const uri = "mongodb+srv://mongodb-example:27017";

Create the Collection创建集合

This example uses two collections:此示例使用两个集合：

• orders: documents that describe individual orders for products in a shop：描述商店中单个产品订单的文档
• products: documents that describe the products that a shop sells：描述商店销售产品的文档

An order can only contain one product. The aggregation uses a one-to-one join to match an order document to the corresponding product document. The aggregation joins the collections by the product_id field that exists in documents in both collections.一个订单只能包含一个产品。聚合使用一对一连接将订单文档与相应的产品文档相匹配。聚合通过两个集合中文档中存在的product_id字段将集合连接起来。

To create the orders and products collections and insert the sample data, add the following code to your application:要创建orders和products集合并插入示例数据，请将以下代码添加到应用程序中：

const orders = aggDB.collection('orders');
const products = aggDB.collection('products');

await orders.insertMany([
  {
    customer_id: 'elise_smith@myemail.com',
    orderdate: new Date('2020-05-30T08:35:52Z'),
    product_id: 'a1b2c3d4',
    value: 431.43,
  },
  {
    customer_id: 'tj@wheresmyemail.com',
    orderdate: new Date('2019-05-28T19:13:32Z'),
    product_id: 'z9y8x7w6',
    value: 5.01,
  },
  {
    customer_id: 'oranieri@warmmail.com',
    orderdate: new Date('2020-01-01T08:25:37Z'),
    product_id: 'ff11gg22hh33',
    value: 63.13,
  },
  {
    customer_id: 'jjones@tepidmail.com',
    orderdate: new Date('2020-12-26T08:55:46Z'),
    product_id: 'a1b2c3d4',
    value: 429.65,
  },
]);

await products.insertMany([
  {
    id: 'a1b2c3d4',
    name: 'Asus Laptop',
    category: 'ELECTRONICS',
    description: 'Good value laptop for students',
  },
  {
    id: 'z9y8x7w6',
    name: 'The Day Of The Triffids',
    category: 'BOOKS',
    description: 'Classic post-apocalyptic novel',
  },
  {
    id: 'ff11gg22hh33',
    name: 'Morphy Richardds Food Mixer',
    category: 'KITCHENWARE',
    description: 'Luxury mixer turning good cakes into great',
  },
  {
    id: 'pqr678st',
    name: 'Karcher Hose Set',
    category: 'GARDEN',
    description: 'Hose + nozzles + winder for tidy storage',
  },
]);

Create the Template App创建模板应用程序

Before you begin following this aggregation tutorial, you must set up a new PHP app. You can use this app to connect to a MongoDB deployment, insert sample data into MongoDB, and run the aggregation pipeline.在开始学习本聚合教程之前，您必须设置一个新的PHP应用程序。您可以使用此应用程序连接到MongoDB部署，将示例数据插入MongoDB，并运行聚合管道。

After you install the library, create a file called agg_tutorial.php. Paste the following code in this file to create an app template for the aggregation tutorials.安装库后，创建一个名为agg_tutorial.php的文件。将以下代码粘贴到此文件中，为聚合教程创建应用程序模板。

<?php

require 'vendor/autoload.php';

// Modify imports for each tutorial as needed.
use MongoDB\Client;
use MongoDB\BSON\UTCDateTime;
use MongoDB\Builder\Pipeline;
use MongoDB\Builder\Stage;
use MongoDB\Builder\Type\Sort;
use MongoDB\Builder\Query;
use MongoDB\Builder\Expression;
use MongoDB\Builder\Accumulator;

use function MongoDB\object;

// Replace the placeholder with your connection string.
$uri = '<connection string>';
$client = new Client($uri);

// Get a reference to relevant collections.
// ... $someColl = $client->agg_tutorials_db->someColl;
// ... $anotherColl = $client->agg_tutorials_db->anotherColl;

// Delete any existing documents in collections if needed.
// ... $someColl->deleteMany([]);

// Insert sample data into the collection or collections.
// ... $someColl->insertMany(...);

// Add code to create pipeline stages within the Pipeline instance.
// ... $pipeline = new Pipeline(...);

// Run the aggregation.
// ... $cursor = $someColl->aggregate($pipeline);

// Print the aggregation results.
foreach ($cursor as $doc) {
    echo json_encode($doc, JSON_PRETTY_PRINT), PHP_EOL;
}

For every tutorial, you must replace the connection string placeholder with your deployment's connection string.对于每个教程，您必须将连接字符串占位符替换为部署的连接字符串。

For example, if your connection string is "mongodb+srv://mongodb-example:27017", your connection string assignment resembles the following:例如，如果连接字符串是"mongodb+srv://mongodb-example:27017"，连接字符串分配类似于以下内容：

$uri = 'mongodb+srv://mongodb-example:27017';

Create the Collection创建集合

This example uses two collections:此示例使用两个集合：

• orders: documents that describe individual orders for products in a shop：描述商店中单个产品订单的文档
• products: documents that describe the products that a shop sells：描述商店销售产品的文档

An order can only contain one product. The aggregation uses a one-to-one join to match an order document to the corresponding product document. The aggregation joins the collections by the product_id field that exists in documents in both collections.一个订单只能包含一个产品。聚合使用一对一连接将订单文档与相应的产品文档相匹配。聚合通过两个集合中文档中存在的product_id字段将集合连接起来。

To create the orders and products collections and insert the sample data, add the following code to your application:要创建orders和products集合并插入示例数据，请将以下代码添加到应用程序中：

$orders = $client->agg_tutorials_db->orders;
$products = $client->agg_tutorials_db->products;

$orders->deleteMany([]);
$products->deleteMany([]);

$orders->insertMany(
    [
        [
            'customer_id' => 'elise_smith@myemail.com',
            'orderdate' => new UTCDateTime(new DateTimeImmutable('2020-05-30T08:35:52')),
            'product_id' => 'a1b2c3d4',
            'value' => 431.43
        ],
        [
            'customer_id' => 'tj@wheresmyemail.com',
            'orderdate' => new UTCDateTime(new DateTimeImmutable('2019-05-28T19:13:32')),
            'product_id' => 'z9y8x7w6',
            'value' => 5.01
        ],
        [
            'customer_id' => 'oranieri@warmmail.com',
            'orderdate' => new UTCDateTime(new DateTimeImmutable('2020-01-01T08:25:37')),
            'product_id' => 'ff11gg22hh33',
            'value' => 63.13,
        ],
        [
            'customer_id' => 'jjones@tepidmail.com',
            'orderdate' => new UTCDateTime(new DateTimeImmutable('2020-12-26T08:55:46')),
            'product_id' => 'a1b2c3d4',
            'value' => 429.65
        ],
    ]
);

$products->insertMany(
    [
        [
            'id' => 'a1b2c3d4',
            'name' => 'Asus Laptop',
            'category' => 'ELECTRONICS',
            'description' => 'Good value laptop for students',
        ],
        [
            'id' => 'z9y8x7w6',
            'name' => 'The Day Of The Triffids',
            'category' => 'BOOKS',
            'description' => 'Classic post-apocalyptic novel',
        ],
        [
            'id' => 'ff11gg22hh33',
            'name' => 'Morphy Richardds Food Mixer',
            'category' => 'KITCHENWARE',
            'description' => 'Luxury mixer turning good cakes into great',
        ],
        [
            'id' => 'pqr678st',
            'name' => 'Karcher Hose Set',
            'category' => 'GARDEN',
            'description' => 'Hose + nozzles + winder for tidy storage',
        ],
    ]
);

Create the Template App创建模板应用程序

Before you begin following this aggregation tutorial, you must set up a new Python app. You can use this app to connect to a MongoDB deployment, insert sample data into MongoDB, and run the aggregation pipeline.在开始学习本聚合教程之前，您必须设置一个新的Python应用程序。您可以使用此应用程序连接到MongoDB部署，将示例数据插入MongoDB，并运行聚合管道。

After you install the library, create a file called agg_tutorial.py. Paste the following code in this file to create an app template for the aggregation tutorials.安装库后，创建一个名为agg_tutorial.py的文件。将以下代码粘贴到此文件中，为聚合教程创建应用程序模板。

# Modify imports for each tutorial as needed.
from pymongo import MongoClient

# Replace the placeholder with your connection string.
uri = "<connection-string>"
client = MongoClient(uri)

try:
    agg_db = client["agg_tutorials_db"]

    # Get a reference to relevant collections.
    # ... some_coll = agg_db["some_coll"]
    # ... another_coll = agg_db["another_coll"]

    # Delete any existing documents in collections if needed.
    # ... some_coll.delete_many({})

    # Insert sample data into the collection or collections.
    # ... some_coll.insert_many(...)

    # Create an empty pipeline array.
    pipeline = []

    # Add code to create pipeline stages.
    # ... pipeline.append({...})

    # Run the aggregation.
    # ... aggregation_result = ...

    # Print the aggregation results.
    for document in aggregation_result:
        print(document)

finally:
    client.close()

For every tutorial, you must replace the connection string placeholder with your deployment's connection string.对于每个教程，您必须将连接字符串占位符替换为部署的连接字符串。

For example, if your connection string is "mongodb+srv://mongodb-example:27017", your connection string assignment resembles the following:例如，如果连接字符串是"mongodb+srv://mongodb-example:27017"，连接字符串分配类似于以下内容：

uri = "mongodb+srv://mongodb-example:27017"

Create the Collection创建集合

This example uses two collections:此示例使用两个集合：

• orders: documents that describe individual orders for products in a shop：描述商店中单个产品订单的文档
• products: documents that describe the products that a shop sells：描述商店销售产品的文档

An order can only contain one product. The aggregation uses a one-to-one join to match an order document to the corresponding product document. The aggregation joins the collections by the product_id field that exists in documents in both collections.一个订单只能包含一个产品。聚合使用一对一连接将订单文档与相应的产品文档相匹配。聚合通过两个集合中文档中存在的product_id字段将集合连接起来。

To create the orders and products collections and insert the sample data, add the following code to your application:要创建orders和products集合并插入示例数据，请将以下代码添加到应用程序中：

orders_coll = agg_db["orders"]
products_coll = agg_db["products"]

order_data = [
    {
        "customer_id": "elise_smith@myemail.com",
        "orderdate": datetime(2020, 5, 30, 8, 35, 52),
        "product_id": "a1b2c3d4",
        "value": 431.43,
    },
    {
        "customer_id": "tj@wheresmyemail.com",
        "orderdate": datetime(2019, 5, 28, 19, 13, 32),
        "product_id": "z9y8x7w6",
        "value": 5.01,
    },
    {
        "customer_id": "oranieri@warmmail.com",
        "orderdate": datetime(2020, 1, 1, 8, 25, 37),
        "product_id": "ff11gg22hh33",
        "value": 63.13,
    },
    {
        "customer_id": "jjones@tepidmail.com",
        "orderdate": datetime(2020, 12, 26, 8, 55, 46),
        "product_id": "a1b2c3d4",
        "value": 429.65,
    },
]

orders_coll.insert_many(order_data)

product_data = [
    {
        "id": "a1b2c3d4",
        "name": "Asus Laptop",
        "category": "ELECTRONICS",
        "description": "Good value laptop for students",
    },
    {
        "id": "z9y8x7w6",
        "name": "The Day Of The Triffids",
        "category": "BOOKS",
        "description": "Classic post-apocalyptic novel",
    },
    {
        "id": "ff11gg22hh33",
        "name": "Morphy Richardds Food Mixer",
        "category": "KITCHENWARE",
        "description": "Luxury mixer turning good cakes into great",
    },
    {
        "id": "pqr678st",
        "name": "Karcher Hose Set",
        "category": "GARDEN",
        "description": "Hose + nozzles + winder for tidy storage",
    },
]

products_coll.insert_many(product_data)

Create the Template App创建模板应用程序

Before you begin following this aggregation tutorial, you must set up a new Ruby app. You can use this app to connect to a MongoDB deployment, insert sample data into MongoDB, and run the aggregation pipeline.在开始学习本聚合教程之前，您必须设置一个新的Ruby应用程序。您可以使用此应用程序连接到MongoDB部署，将示例数据插入MongoDB，并运行聚合管道。

After you install the driver, create a file called agg_tutorial.rb. Paste the following code in this file to create an app template for the aggregation tutorials.安装驱动程序后，创建一个名为agg_tutorial.rb的文件。将以下代码粘贴到此文件中，为聚合教程创建应用程序模板。

# typed: strict
require 'mongo'
require 'bson'

# Replace the placeholder with your connection string.
uri = "<connection string>"

Mongo::Client.new(uri) do |client|

  agg_db = client.use('agg_tutorials_db')

  # Get a reference to relevant collections.
  # ... some_coll = agg_db[:some_coll]

  # Delete any existing documents in collections if needed.
  # ... some_coll.delete_many({})

  # Insert sample data into the collection or collections.
  # ... some_coll.insert_many( ... )

  # Add code to create pipeline stages within the array.
  # ... pipeline = [ ... ]

  # Run the aggregation.
  # ... aggregation_result = some_coll.aggregate(pipeline)

  # Print the aggregation results.
  aggregation_result.each do |doc|
    puts doc
  end

end

For every tutorial, you must replace the connection string placeholder with your deployment's connection string.对于每个教程，您必须将连接字符串占位符替换为部署的连接字符串。

For example, if your connection string is "mongodb+srv://mongodb-example:27017", your connection string assignment resembles the following:例如，如果连接字符串是"mongodb+srv://mongodb-example:27017"，连接字符串分配类似于以下内容：

uri = "mongodb+srv://mongodb-example:27017"

Create the Collection创建集合

This example uses two collections:此示例使用两个集合：

• orders: documents that describe individual orders for products in a shop：描述商店中单个产品订单的文档
• products: documents that describe the products that a shop sells：描述商店销售产品的文档

An order can only contain one product. The aggregation uses a one-to-one join to match an order document to the corresponding product document. The aggregation joins the collections by the product_id field that exists in documents in both collections.一个订单只能包含一个产品。聚合使用一对一连接将订单文档与相应的产品文档相匹配。聚合通过两个集合中文档中存在的product_id字段将集合连接起来。

To create the orders and products collections and insert the sample data, add the following code to your application:要创建orders和products集合并插入示例数据，请将以下代码添加到应用程序中：

orders = agg_db[:orders]
products = agg_db[:products]

orders.delete_many({})
products.delete_many({})

orders.insert_many(
  [
    {
      customer_id: "elise_smith@myemail.com",
      orderdate: DateTime.parse("2020-05-30T08:35:52Z"),
      product_id: "a1b2c3d4",
      value: 431.43,
    },
    {
      customer_id: "tj@wheresmyemail.com",
      orderdate: DateTime.parse("2019-05-28T19:13:32Z"),
      product_id: "z9y8x7w6",
      value: 5.01,
    },
    {
      customer_id: "oranieri@warmmail.com",
      orderdate: DateTime.parse("2020-01-01T08:25:37Z"),
      product_id: "ff11gg22hh33",
      value: 63.13,
    },
    {
      customer_id: "jjones@tepidmail.com",
      orderdate: DateTime.parse("2020-12-26T08:55:46Z"),
      product_id: "a1b2c3d4",
      value: 429.65,
    },
  ]
)

products.insert_many(
  [
    {
      id: "a1b2c3d4",
      name: "Asus Laptop",
      category: "ELECTRONICS",
      description: "Good value laptop for students",
    },
    {
      id: "z9y8x7w6",
      name: "The Day Of The Triffids",
      category: "BOOKS",
      description: "Classic post-apocalyptic novel",
    },
    {
      id: "ff11gg22hh33",
      name: "Morphy Richardds Food Mixer",
      category: "KITCHENWARE",
      description: "Luxury mixer turning good cakes into great",
    },
    {
      id: "pqr678st",
      name: "Karcher Hose Set",
      category: "GARDEN",
      description: "Hose + nozzles + winder for tidy storage",
    },
  ]
)

Create the Template App创建模板应用程序

Before you begin following this aggregation tutorial, you must set up a new Rust app. You can use this app to connect to a MongoDB deployment, insert sample data into MongoDB, and run the aggregation pipeline.在开始学习本聚合教程之前，您必须设置一个新的Rust应用程序。您可以使用此应用程序连接到MongoDB部署，将示例数据插入MongoDB，并运行聚合管道。

After you install the driver, create a file called agg-tutorial.rs. Paste the following code in this file to create an app template for the aggregation tutorials.安装驱动程序后，创建一个名为agg-tutorial.rs的文件。将以下代码粘贴到此文件中，为聚合教程创建应用程序模板。

use mongodb::{
    bson::{doc, Document},
    options::ClientOptions,
    Client,
};
use futures::stream::TryStreamExt;
use std::error::Error;

// Define structs.
// #[derive(Debug, Serialize, Deserialize)]
// struct MyStruct { ... }

#[tokio::main]
async fn main() mongodb::error::Result<()> {
    // Replace the placeholder with your connection string.
    let uri = "<connection string>";
    let client = Client::with_uri_str(uri).await?;

    let agg_db = client.database("agg_tutorials_db");

    // Get a reference to relevant collections.
    // ... let some_coll: Collection<T> = agg_db.collection("...");
    // ... let another_coll: Collection<T> = agg_db.collection("...");

    // Delete any existing documents in collections if needed.
    // ... some_coll.delete_many(doc! {}).await?;

    // Insert sample data into the collection or collections.
    // ... some_coll.insert_many(vec![...]).await?;

    // Create an empty pipeline.
    let mut pipeline = Vec::new();

    // Add code to create pipeline stages.
    // pipeline.push(doc! { ... });

    // Run the aggregation and print the results.
    let mut results = some_coll.aggregate(pipeline).await?;
    while let Some(result) = results.try_next().await? {
       println!("{:?}\n", result);
    }
    Ok(())
}

For every tutorial, you must replace the connection string placeholder with your deployment's connection string.对于每个教程，您必须将连接字符串占位符替换为部署的连接字符串。

For example, if your connection string is "mongodb+srv://mongodb-example:27017", your connection string assignment resembles the following:例如，如果连接字符串是"mongodb+srv://mongodb-example:27017"，连接字符串分配类似于以下内容：

let uri = "mongodb+srv://mongodb-example:27017";

Create the Collection创建集合

This example uses two collections:此示例使用两个集合：

• orders: documents that describe individual orders for products in a shop：描述商店中单个产品订单的文档
• products: documents that describe the products that a shop sells：描述商店销售产品的文档

An order can only contain one product. The aggregation uses a one-to-one join to match an order document to the corresponding product document. The aggregation joins the collections by the product_id field that exists in documents in both collections.一个订单只能包含一个产品。聚合使用一对一连接将订单文档与相应的产品文档相匹配。聚合通过两个集合中文档中存在的product_id字段将集合连接起来。

First, create Rust structs to model the data in the orders and products collections:首先，创建Rust结构体来对orders和products集合中的数据进行建模：

#[derive(Debug, Serialize, Deserialize)]
struct Order {
    customer_id: String,
    order_date: DateTime,
    product_id: String,
    value: f32,
}

#[derive(Debug, Serialize, Deserialize)]
struct Product {
    id: String,
    name: String,
    category: String,
    description: String,
}

To create the orders and products collections and insert the sample data, add the following code to your application:要创建orders和products集合并插入示例数据，请将以下代码添加到应用程序中：

let orders: Collection<Order> = agg_db.collection("orders");
let products: Collection<Product> = agg_db.collection("products");

orders.delete_many(doc! {}).await?;
products.delete_many(doc! {}).await?;

let order_docs = vec![
    Order {
        customer_id: "elise_smith@myemail.com".to_string(),
        order_date: DateTime::builder().year(2020).month(5).day(30).hour(8).minute(35).second(52).build().unwrap(),
        product_id: "a1b2c3d4".to_string(),
        value: 431.43,
    },
    Order {
        customer_id: "tj@wheresmyemail.com".to_string(),
        order_date: DateTime::builder().year(2019).month(5).day(28).hour(19).minute(13).second(32).build().unwrap(),
        product_id: "z9y8x7w6".to_string(),
        value: 5.01,
    },
    Order {
        customer_id: "oranieri@warmmail.com".to_string(),
        order_date: DateTime::builder().year(2020).month(1).day(1).hour(8).minute(25).second(37).build().unwrap(),
        product_id: "ff11gg22hh33".to_string(),
        value: 63.13,
    },
    Order {
        customer_id: "jjones@tepidmail.com".to_string(),
        order_date: DateTime::builder().year(2020).month(12).day(26).hour(8).minute(55).second(46).build().unwrap(),
        product_id: "a1b2c3d4".to_string(),
        value: 429.65,
    },
];
orders.insert_many(order_docs).await?;

let product_docs = vec![
    Product {
        id: "a1b2c3d4".to_string(),
        name: "Asus Laptop".to_string(),
        category: "ELECTRONICS".to_string(),
        description: "Good value laptop for students".to_string(),
    },
    Product {
        id: "z9y8x7w6".to_string(),
        name: "The Day Of The Triffids".to_string(),
        category: "BOOKS".to_string(),
        description: "Classic post-apocalyptic novel".to_string(),
    },
    Product {
        id: "ff11gg22hh33".to_string(),
        name: "Morphy Richardds Food Mixer".to_string(),
        category: "KITCHENWARE".to_string(),
        description: "Luxury mixer turning good cakes into great".to_string(),
    },
    Product {
        id: "pqr678st".to_string(),
        name: "Karcher Hose Set".to_string(),
        category: "GARDEN".to_string(),
        description: "Hose + nozzles + winder for tidy storage".to_string(),
    },
];
products.insert_many(product_docs).await?;

Create the Template App创建模板应用程序

Before you begin following an aggregation tutorial, you must set up a new Scala app. You can use this app to connect to a MongoDB deployment, insert sample data into MongoDB, and run the aggregation pipeline.在开始学习聚合教程之前，您必须设置一个新的Scala应用程序。您可以使用此应用程序连接到MongoDB部署，将示例数据插入MongoDB，并运行聚合管道。

After you install the driver, create a file called AggTutorial.scala. Paste the following code in this file to create an app template for the aggregation tutorials.安装驱动程序后，创建一个名为AggTutorial.scala的文件。将以下代码粘贴到此文件中，为聚合教程创建应用程序模板。

package org.example;

// Modify imports for each tutorial as needed.
import org.mongodb.scala.MongoClient
import org.mongodb.scala.bson.Document
import org.mongodb.scala.model.{Accumulators, Aggregates, Field, Filters, Variable}

import java.text.SimpleDateFormat

object FilteredSubset {

  def main(args: Array[String]): Unit = {

    // Replace the placeholder with your connection string.
    val uri = "<connection string>"
    val mongoClient = MongoClient(uri)
    Thread.sleep(1000)

    val aggDB = mongoClient.getDatabase("agg_tutorials_db")

    // Get a reference to relevant collections.
    // ... val someColl = aggDB.getCollection("someColl")
    // ... val anotherColl = aggDB.getCollection("anotherColl")

    // Delete any existing documents in collections if needed.
    // ... someColl.deleteMany(Filters.empty()).subscribe(...)

    // If needed, create the date format template.
    val dateFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss")

    // Insert sample data into the collection or collections.
    // ... someColl.insertMany(...).subscribe(...)

    Thread.sleep(1000)

    // Add code to create pipeline stages within the Seq.
    // ... val pipeline = Seq(...)

    // Run the aggregation and print the results.
    // ... someColl.aggregate(pipeline).subscribe(...)

    Thread.sleep(1000)
    mongoClient.close()
  }
}

For every tutorial, you must replace the connection string placeholder with your deployment's connection string.对于每个教程，您必须将连接字符串占位符替换为部署的连接字符串。

For example, if your connection string is "mongodb+srv://mongodb-example:27017", your connection string assignment resembles the following:例如，如果连接字符串是"mongodb+srv://mongodb-example:27017"，连接字符串分配类似于以下内容：

val uri = "mongodb+srv://mongodb-example:27017"

Create the Collection创建集合

This example uses two collections:此示例使用两个集合：

• orders: documents that describe individual orders for products in a shop：描述商店中单个产品订单的文档
• products: documents that describe the products that a shop sells：描述商店销售产品的文档

An order can only contain one product. The aggregation uses a one-to-one join to match an order document to the corresponding product document. The aggregation joins the collections by the product_id field that exists in documents in both collections.一个订单只能包含一个产品。聚合使用一对一连接将订单文档与相应的产品文档相匹配。聚合通过两个集合中文档中存在的product_id字段将集合连接起来。

To create the orders and products collections and insert the sample data, add the following code to your application:要创建orders和products集合并插入示例数据，请将以下代码添加到应用程序中：

val orders = aggDB.getCollection("orders")
val products = aggDB.getCollection("products")

orders.deleteMany(Filters.empty()).subscribe(
  _ => {},
  e => println("Error: " + e.getMessage),
)

products.deleteMany(Filters.empty()).subscribe(
  _ => {},
  e => println("Error: " + e.getMessage),
)

val dateFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss")

orders.insertMany(
  Seq(
    Document(
      "customer_id" -> "elise_smith@myemail.com",
      "orderdate" -> dateFormat.parse("2020-05-30T08:35:52"),
      "product_id" -> "a1b2c3d4",
      "value" -> 431.43
    ),
    Document(
      "customer_id" -> "tj@wheresmyemail.com",
      "orderdate" -> dateFormat.parse("2019-05-28T19:13:32"),
      "product_id" -> "z9y8x7w6",
      "value" -> 5.01
    ),
    Document(
      "customer_id" -> "oranieri@warmmail.com",
      "orderdate" -> dateFormat.parse("2020-01-01T08:25:37"),
      "product_id" -> "ff11gg22hh33",
      "value" -> 63.13
    ),
    Document(
      "customer_id" -> "jjones@tepidmail.com",
      "orderdate" -> dateFormat.parse("2020-12-26T08:55:46"),
      "product_id" -> "a1b2c3d4",
      "value" -> 429.65
    )
  )
).subscribe(
  _ => {},
  e => println("Error: " + e.getMessage),
)

products.insertMany(
  Seq(
    Document(
      "id" -> "a1b2c3d4",
      "name" -> "Asus Laptop",
      "category" -> "ELECTRONICS",
      "description" -> "Good value laptop for students"
    ),
    Document(
      "id" -> "z9y8x7w6",
      "name" -> "The Day Of The Triffids",
      "category" -> "BOOKS",
      "description" -> "Classic post-apocalyptic novel"
    ),
    Document(
      "id" -> "ff11gg22hh33",
      "name" -> "Morphy Richardds Food Mixer",
      "category" -> "KITCHENWARE",
      "description" -> "Luxury mixer turning good cakes into great"
    ),
    Document(
      "id" -> "pqr678st",
      "name" -> "Karcher Hose Set",
      "category" -> "GARDEN",
      "description" -> "Hose + nozzles + winder for tidy storage"
    )
  )
).subscribe(
  _ => {},
  e => println("Error: " + e.getMessage),
)