Retrieve Distinct Values检索不同的值

Sample Documents样本文件

To follow the examples in this guide, use the following code snippet to insert documents that describe restaurants into the myDB.restaurants collection:要遵循本指南中的示例，请使用以下代码片段将描述餐厅的文档插入到myDB.restaurants集合中：

const myDB = client.db("myDB");
const myColl = myDB.collection("restaurants");

await myColl.insertMany([
  { "_id": 1, "restaurant": "White Bear", "borough": "Queens", "cuisine": "Chinese" },
  { "_id": 2, "restaurant": "Via Carota", "borough": "Manhattan", "cuisine": "Italian" },
  { "_id": 3, "restaurant": "Borgatti's", "borough": "Bronx", "cuisine": "Italian" },
  { "_id": 4, "restaurant": "Tanoreen", "borough": "Brooklyn", "cuisine": "Middle Eastern" },
  { "_id": 5, "restaurant": "Äpfel", "borough": "Queens", "cuisine": "German" },
  { "_id": 6, "restaurant": "Samba Kitchen", "borough": "Manhattan", "cuisine": "Brazilian" },
]);

Document Field Parameter文档字段参数

Pass the name of the document field to return a list of the field's unique values.传递文档字段的名称以返回字段唯一值的列表。

Example示例

The "Queens" and "Manhattan" borough values each appear more than once in the sample documents. However, the following example retrieves the unique values of the borough field:"Queens"（皇后区）和"Manhattan"（曼哈顿区）的数值在样本文件中都出现了多次。但是，以下示例检索了borough字段的唯一值：

// specify "borough" as the field to return values for指定“borough”作为返回值的字段
const cursor = myColl.distinct("borough");
for await (const doc of cursor) {
  console.dir(doc);
}

This code outputs the following borough values:此代码输出以下borough（行政区）值：

[ "Bronx", "Brooklyn", "Manhattan", "Queens" ]

Query Parameter查询参数

You can specify a query parameter to return unique values for documents that match your query.您可以指定一个查询参数，为与查询匹配的文档返回唯一值。

Visit Specify a Query for more information on constructing a query filter.有关构建查询筛选器的详细信息，请访问指定查询。

// exclude Brooklyn restaurants from the output将布鲁克林餐厅排除在输出之外
const query = { borough: { $ne: "Brooklyn" }};

// find the filtered distinct values of "cuisine"找到“cuisine”的筛选后的不同值
const cursor = myColl.distinct("cuisine", query);
for await (const doc of cursor) {
  console.dir(doc);
}

[ "Brazilian", "Chinese", "German", "Italian" ]

Options Parameter选项参数

You can specify the collation to the distinct() method by defining a collation field as an options parameter. This field allows you to set regional rules for string ordering and comparisons.您可以通过将collation字段定义为options参数来为distinct()方法指定排序规则。此字段允许您设置字符串排序和比较的区域规则。

See the Collation section of the Configure CRUD Operations guide for instructions on applying collations.有关应用排序规则的说明，请参阅配置CRUD操作指南的排序规则部分。

// define an empty query document定义一个空查询文档
const query = {};
// specify German string ordering conventions指定德语字符串排序约定
const options = { collation: { locale: "de" }};

const cursor = myColl.distinct("restaurant", query, options);
for await (const doc of cursor) {
  console.dir(doc);
}

[ "Äpfel", "Borgatti's", "Samba Kitchen", "Tanoreen", "Via Carota", "White Bear" ]

[ "Borgatti's", "Samba Kitchen", "Tanoreen", "Via Carota", "White Bear", "Äpfel" ]

distinct() Example: Full Filedistinct()示例：完整文件

The following snippet retrieves a list of distinct values for the year document field from the movies collection. It uses a query document to match movies that include "Barbara Streisand" in the director array.以下代码段从movies集合中检索year文档字段的不同值列表。它使用查询文档来匹配director（导演）数组中包含"Barbara Streisand"（芭芭拉·史翠珊）的电影。

import { MongoClient } from "mongodb";

// Replace the uri string with your MongoDB deployment's connection string.将uri字符串替换为MongoDB部署的连接字符串。
const uri = "<connection string uri>";

const client = new MongoClient(uri);

async function run() {
  try {
    
    // Get the database and collection on which to run the operation获取要在其上运行操作的数据库和集合
    const database = client.db("sample_mflix");
    const movies = database.collection("movies");

    // Specify the document field to find distinct values for指定文档字段以查找不同的值
    const fieldName = "year";

    // Specify an optional query document to narrow results指定一个可选的查询文档以缩小结果范围
    const query = { directors: "Barbra Streisand" };

    // Execute the distinct operation执行独特的操作
    const distinctValues = await movies.distinct(fieldName, query);

    // Print the result打印结果
    console.log(distinctValues);
  } finally {
    await client.close();
  }
}
run().catch(console.dir);

import { MongoClient } from "mongodb";

// Replace the uri string with your MongoDB deployment's connection string.将uri字符串替换为MongoDB部署的连接字符串。
const uri = "<connection string uri>";

const client = new MongoClient(uri);

interface Movie {
  directors: string;
  year: number;
}

async function run() {
  try {
    // define a database and collection on which to run the method定义要在其上运行该方法的数据库和集合
    const database = client.db("sample_mflix");
    const movies = database.collection<Movie>("movies");

    const distinctValues = await movies.distinct("year", {
      directors: "Barbra Streisand",
    });

    console.log(distinctValues);
  } finally {
    await client.close();
  }
}
run().catch(console.dir);

Running the preceding example, results in the following output:运行前面的示例，得到以下输出：

[ 1983, 1991, 1996 ]