Faceted Classification分面分类

Minimum MongoDB Version: 4.2

Scenario情形

You want to provide a faceted search capability on your retail website to enable customers to refine their product search by selecting specific characteristics against the product results listed in the web page. 您希望在零售网站上提供多方面的搜索功能，使客户能够通过根据网页中列出的产品结果选择特定特征来优化产品搜索。It is beneficial to classify the products by different dimensions, where each dimension, or facet, corresponds to a particular field in a product record (e.g. product rating, product price). 按不同的维度对产品进行分类是有益的，其中每个维度或方面都对应于产品记录中的特定字段（例如，产品评级、产品价格）。Each facet should be broken down into sub-ranges so that a customer can select a specific sub-range (4 - 5 stars) for a particular facet (e.g. rating). 每个方面都应该细分为子范围，这样客户就可以为特定方面（例如评级）选择特定的子范围（4-5颗星）。The aggregation pipeline will analyse the products collection by each facet's field (rating and price) to determine each facet's spread of values.聚合管道将按每个方面的领域（评级和价格）分析产品集合，以确定每个方面的价值分布。

Sample Data Population样本数据总体

Drop any old version of the database (if it exists) and then populate a new products collection with 16 documents (the database commands have been split in two to enable your clipboard to hold all the text - ensure you copy and execute each of the two sections):删除数据库的任何旧版本（如果存在），然后用16个文档填充新products集合（数据库命令已一分为二，以使剪贴板能够保存所有文本-确保复制并执行这两个部分中的每一个）：

 -Part 1-

db = db.getSiblingDB("book-faceted-classfctn");
db.dropDatabase();

// Insert first 8 records into the collection将前8条记录插入集合
db.products.insertMany([
  {
    "name": "Asus Laptop",
    "category": "ELECTRONICS",
    "description": "Good value laptop for students",
    "price": NumberDecimal("431.43"),
    "rating": NumberDecimal("4.2"),
  },
  {
    "name": "The Day Of The Triffids",
    "category": "BOOKS",
    "description": "Classic post-apocalyptic novel",
    "price": NumberDecimal("5.01"),
    "rating": NumberDecimal("4.8"),
  },
  {
    "name": "Morphy Richardds Food Mixer",
    "category": "KITCHENWARE",
    "description": "Luxury mixer turning good cakes into great",
    "price": NumberDecimal("63.13"),
    "rating": NumberDecimal("3.8"),
  },
  {
    "name": "Karcher Hose Set",
    "category": "GARDEN",
    "description": "Hose + nosels + winder for tidy storage",
    "price": NumberDecimal("22.13"),
    "rating": NumberDecimal("4.3"),
  },
  {
    "name": "Oak Coffee Table",
    "category": "HOME",
    "description": "size is 2m x 0.5m x 0.4m",
    "price": NumberDecimal("22.13"),
    "rating": NumberDecimal("3.8"),
  },
  {
    "name": "Lenovo Laptop",
    "category": "ELECTRONICS",
    "description": "High spec good for gaming",
    "price": NumberDecimal("1299.99"),
    "rating": NumberDecimal("4.1"),
  },
  {
    "name": "One Day in the Life of Ivan Denisovich",
    "category": "BOOKS",
    "description": "Brutal life in a labour camp",
    "price": NumberDecimal("4.29"),
    "rating": NumberDecimal("4.9"),
  },
  {
    "name": "Russell Hobbs Chrome Kettle",
    "category": "KITCHENWARE",
    "description": "Nice looking budget kettle",
    "price": NumberDecimal("15.76"),
    "rating": NumberDecimal("3.9"),
  },
]);

 -Part 2-

// Insert second 8 records into the collection将第二个8条记录插入集合
db.products.insertMany([  
  {
    "name": "Tiffany Gold Chain",
    "category": "JEWELERY",
    "description": "Looks great for any age and gender",
    "price": NumberDecimal("582.22"),
    "rating": NumberDecimal("4.0"),
  },
  {
    "name": "Raleigh Racer 21st Century Classic",
    "category": "BICYCLES",
    "description": "Modern update to a classic 70s bike design",
    "price": NumberDecimal("523.00"),
    "rating": NumberDecimal("4.5"),
  },
  {
    "name": "Diesel Flare Jeans",
    "category": "CLOTHES",
    "description": "Top end casual look",
    "price": NumberDecimal("129.89"),
    "rating": NumberDecimal("4.3"),
  },
  {
    "name": "Jazz Silk Scarf",
    "category": "CLOTHES",
    "description": "Style for the winder months",
    "price": NumberDecimal("28.39"),
    "rating": NumberDecimal("3.7"),
  },
  {
    "name": "Dell XPS 13 Laptop",
    "category": "ELECTRONICS",
    "description": "Developer edition",
    "price": NumberDecimal("1399.89"),
    "rating": NumberDecimal("4.4"),
  },
  {
    "name": "NY Baseball Cap",
    "category": "CLOTHES",
    "description": "Blue & white",
    "price": NumberDecimal("18.99"),
    "rating": NumberDecimal("4.0"),
  },
  {
    "name": "Tots Flower Pots",
    "category": "GARDEN",
    "description": "Set of three",
    "price": NumberDecimal("9.78"),
    "rating": NumberDecimal("4.1"),
  },  
  {
    "name": "Picky Pencil Sharpener",
    "category": "Stationery",
    "description": "Ultra budget",
    "price": NumberDecimal("0.67"),
    "rating": NumberDecimal("1.2"),
  },  
]);

Aggregation Pipeline聚合管道

Define a pipeline ready to perform the aggregation:定义准备执行聚合的管道：

var pipeline = [
  // Group products by 2 facets: 1) by price ranges, 2) by rating ranges按2个方面对产品进行分组：1）按价格范围，2）按评级范围
  {"$facet": {

    // Group by price ranges
    "by_price": [
      // Group into 3 ranges: inexpensive small price range to expensive large price range分为3个范围：便宜的小价格范围到昂贵的大价格范围
      {"$bucketAuto": {
        "groupBy": "$price",
        "buckets": 3,
        "granularity": "1-2-5",
        "output": {
          "count": {"$sum": 1},
          "products": {"$push": "$name"},
        },
      }},
      
      // Tag range info as "price_range"
      {"$set": {
        "price_range": "$_id",
      }},         
      
      // Omit unwanted fields
      {"$unset": [
        "_id",
      ]},         
    ],

    // Group by rating ranges按评级范围分组
    "by_rating": [
      // Group products evenly across 5 rating ranges from low to high在从低到高的5个评级范围内对产品进行平均分组
      {"$bucketAuto": {
        "groupBy": "$rating",
        "buckets": 5,
        "output": {
          "count": {"$sum": 1},
          "products": {"$push": "$name"},
        },
      }},
      
      // Tag range info as "rating_range"将范围信息标记为“rating_range”
      {"$set": {
        "rating_range": "$_id",
      }},         
      
      // Omit unwanted fields
      {"$unset": [
        "_id",
      ]},         
    ],
  }},  
];

Execution执行

Execute the aggregation using the defined pipeline and also view its explain plan:使用定义的管道执行聚合，并查看其解释计划：

db.products.aggregate(pipeline);
db.products.explain("executionStats").aggregate(pipeline);

Expected Results预期结果

A single document should be returned, which contains 2 facets (keyed off by_price and by_rating respectively), where each facet shows its sub-ranges of values and the products belonging to each sub-range, as shown below:应返回一个单独的文档，其中包含2个方面（分别由by_price和by_rating键控），其中每个方面显示其值的子范围和属于每个子范围的产品，如下所示：

[
  {
    by_price: [
      {
        count: 6,
        products: [
          'Picky Pencil Sharpener', 'One Day in the Life of Ivan Denisovich', 
          'The Day Of The Triffids', 'Tots Flower Pots', 'Russell Hobbs Chrome Kettle',
          'NY Baseball Cap'
        ],
        price_range: {
          min: NumberDecimal('0.500000000000000'), max: NumberDecimal('20.0000000000000')
        }
      },
      {
        count: 5,
        products: [
          'Karcher Hose Set', 'Oak Coffee Table', 'Jazz Silk Scarf',
          'Morphy Richardds Food Mixer', 'Diesel Flare Jeans'
        ],
        price_range: {
          min: NumberDecimal('20.0000000000000'), max: NumberDecimal('200.0000000000000')
        }
      },
      {
        count: 5,
        products: [
          'Asus Laptop', 'Raleigh Racer 21st Century Classic', 'Tiffany Gold Chain',
          'Lenovo Laptop', 'Dell XPS 13 Laptop'
        ],
        price_range: {
          min: NumberDecimal('200.0000000000000'), max: NumberDecimal('2000.0000000000000')
        }
      }
    ],
    by_rating: [
      {
        count: 4,
        products: [
          'Picky Pencil Sharpener', 'Jazz Silk Scarf', 'Morphy Richardds Food Mixer',
          'Oak Coffee Table'
        ],
        rating_range: { min: NumberDecimal('1.2'), max: NumberDecimal('3.9') }
      },
      {
        count: 3,
        products: [
          'Russell Hobbs Chrome Kettle', 'Tiffany Gold Chain', 'NY Baseball Cap'
        ],
        rating_range: { min: NumberDecimal('3.9'), max: NumberDecimal('4.1') }
      },
      {
        count: 3,
        products: [ 'Lenovo Laptop', 'Tots Flower Pots', 'Asus Laptop' ],
        rating_range: { min: NumberDecimal('4.1'), max: NumberDecimal('4.3') }
      },
      {
        count: 3,
        products: [
          'Karcher Hose Set', 'Diesel Flare Jeans', 'Dell XPS 13 Laptop'
        ],
        rating_range: { min: NumberDecimal('4.3'), max: NumberDecimal('4.5') }
      },
      {
        count: 3,
        products: [
          'Raleigh Racer 21st Century Classic', 'The Day Of The Triffids',
          'One Day in the Life of Ivan Denisovich'
        ],
        rating_range: { min: NumberDecimal('4.5'), max: NumberDecimal('4.9') }
      }
    ]
  }
]

Observations观察