## **1、MongoDB 聚合管道（Aggregation Pipeline）** 使用聚合管道可以對集合中的文檔進行變換和組合。 實際項目：表關聯查詢、數據的統計。 MongoDB 中使用 db.COLLECTION\_NAME.aggregate(\[{\<stage\>},...\]) 方法 來構建和使用聚合管道。先看下官網給的實例，感受一下聚合管道的用法。  ## **2、MongoDB Aggregation 管道操作符與表達式** | 管道操作符 | Description | | --- | --- | | $project | 增加、刪除、重命名字段 | | $match | 條件匹配。只滿足條件的文檔才能進入下 一階段 | | $limit | 限制結果的數量 | | $skip | 跳過文檔的數量 | | $sort | 條件排序。 | | $group | 條件組合結果 統計 | | $lookup | $lookup 操作符 用以引入其它集合的數 據 （表關聯查詢） | **SQL 和 NOSQL 對比:** | WHERE | $match | | --- | --- | | GROUP BY | $group | | HAVING | $match | | SELECT | $project | | ORDER BY | $sort | | LIMIT | $limit | | SUM() | $sum | | COUNT() | $sum | | join | $lookup | **管道表達式:** 管道操作符作為“鍵”,所對應的“值”叫做管道表達式。 例如{$match:{status:"A"}}，$match 稱為管道操作符，而 status:"A"稱為管道表達式， 是管道操作符的操作數(Operand)。 每個管道表達式是一個文檔結構，它是由字段名、字段值、和一些表達式操作符組成的。 | 常用表達式操作符 | Description | | --- | --- | | $addToSet | 將文檔指定字段的值去重 | | $max | 文檔指定字段的最大值 | | $min | 文檔指定字段的最小值 | | $sum | 文檔指定字段求和 | | $avg | 文檔指定字段求平均 | | $gt | 大于給定值 | | $lt | 小于給定值 | | $eq | 等于給定值 | ## **3、 數據模擬** ``` db.order.insert({"order_id":"1","uid":10,"trade_no":"111","all_price":100,"all_num":2}) db.order.insert({"order_id":"2","uid":7,"trade_no":"222","all_price":90,"all_num":2}) db.order.insert({"order_id":"3","uid":9,"trade_no":"333","all_price":20,"all_num":6}) db.order_item.insert({"order_id":"1","title":"商品鼠標 1","price":50,num:1}) db.order_item.insert({"order_id":"1","title":"商品鍵盤 2","price":50,num:1}) db.order_item.insert({"order_id":"1","title":"商品鍵盤 3","price":0,num:1}) db.order_item.insert({"order_id":"2","title":"牛奶","price":50,num:1}) db.order_item.insert({"order_id":"2","title":"酸奶","price":40,num:1}) db.order_item.insert({"order_id":"3","title":"礦泉水","price":2,num:5}) db.order_item.insert({"order_id":"3","title":"毛巾","price":10,num:1}) ```  ## **4、 $project** 修改文檔的結構，可以用來重命名、增加或刪除文檔中的字段。 要求查找 order 只返回文檔中 trade\_no 和 all\_price 字段 ``` db.order.aggregate([ { $project:{ trade_no:1, all_price:1 } } ]) ```  ## **5、 $match** **作用** 用于過濾文檔。用法類似于 find() 方法中的參數。 ``` db.order.aggregate([ { $project:{ trade_no:1, all_price:1 } }, { $match:{"all_price":{$gte:90}} } ] ) ```  ## **6、 $group** 將集合中的文檔進行分組，可用于統計結果。 統計每個訂單的訂單數量，按照訂單號分組 ``` db.order_item.aggregate( [ { $group: {_id: "$order_id", total: {$sum: "$num"}} } ] ) ```  ## **7、 $sort** 將集合中的文檔進行排序。 ``` db.order.aggregate([ { $project:{ trade_no:1, all_price:1 } }, { $match:{"all_price":{$gte:90}} }, { $sort:{"all_price":-1} } ]) ```   ## **8、 $limit** ``` db.order.aggregate([ { $project:{ trade_no:1, all_price:1 } }, { $match:{"all_price":{$gte:90}} }, { $sort:{"all_price":-1} }, { $limit:1 } ]) ```  ## **9、 $skip** ``` db.order.aggregate([ { $project:{ trade\_no:1, all_price:1 } }, { $match:{"all_price":{$gte:90}} }, { $sort:{"all_price":-1} }, { $skip:1 } ]) ```  ## **10、 $lookup 表關聯** ``` db.order.aggregate([ { $lookup: { from: "order_item", localField: "order_id", foreignField: "order_id", as: "items" } } ]) { "_id": ObjectId("5b743d8c2c327f8d1b360540"), "order_id": "1", "uid": 10, "trade_no": "111", "all_price": 100, "all_num": 2, "items": [ { "_id": ObjectId("5b743d9c2c327f8d1b360543"), "order_id": "1", "title": "商品鼠標 1", "price": 50, "num": 1 }, { "_id": ObjectId("5b743da12c327f8d1b360544"), "order_id": "1", "title": "商品鍵盤 2", "price": 50, "num": 1 }, { "_id": ObjectId("5b74f457089f78dc8f0a4f3b"), "order_id": "1", "title": "商品鍵盤 3", "price": 0, "num": 1 } ] } { "_id": ObjectId("5b743d902c327f8d1b360541"), "order_id": "2", "uid": 7, "trade_no": "222", "all_price": 90, "all_num": 2, "items": [ { "_id": ObjectId("5b743da52c327f8d1b360545"), "order_id": "2", "title": "牛奶", "price": 50, "num": 1 }, { "_id": ObjectId("5b743da92c327f8d1b360546"), "order_id": "2", "title": "酸奶", "price": 40, "num": 1 } ] } { "_id": ObjectId("5b743d962c327f8d1b360542"), "order_id": "3", "uid": 9, "trade_no": "333", "all_price": 20, "all_num": 6, "items": [ { "_id": ObjectId("5b743dad2c327f8d1b360547"), "order_id": "3", "title": "礦泉水", "price": 2, "num": 5 }, { "_id": ObjectId("5b743dff2c327f8d1b360548"), "order_id": "3", "title": "毛巾", "price": 10, "num": 1 } ] } db.order.aggregate([ { $lookup: { from: "order_item", localField: "order_id", foreignField: "order_id", as: "items" } }, { $match:{"all_price":{$gte:90}} } ]) { "_id": ObjectId("5b743d8c2c327f8d1b360540"), "order_id": "1", "uid": 10, "trade_no": "111", "all_price": 100, "all_num": 2, "items": [ { "_id": ObjectId("5b743d9c2c327f8d1b360543"), "order_id": "1", "title": "商品鼠標 1", "price": 50, "num": 1 }, { "_id": ObjectId("5b743da12c327f8d1b360544"), "order_id": "1", "title": "商品鍵盤 2", "price": 50, "num": 1 }, { "_id": ObjectId("5b74f457089f78dc8f0a4f3b"), "order_id": "1", "title": "商品鍵盤 3", "price": 0, "num": 1 } ] } { "_id": ObjectId("5b743d902c327f8d1b360541"), "order_id": "2", "uid": 7, "trade_no": "222", "all_price": 90, "all_num": 2, "items": [ { "_id": ObjectId("5b743da52c327f8d1b360545"), "order_id": "2", "title": "牛奶", "price": 50, "num": 1 }, { "_id": ObjectId("5b743da92c327f8d1b360546"), "order_id": "2", "title": "酸奶", "price": 40, "num": 1 } ] } db.order.aggregate([ { $lookup: { from: "order\_item", localField: "order_id", foreignField: "order_id", as: "items" } }, { $project:{ trade_no:1, all\_price:1,items:1 } }, { $match:{"all\_price":{$gte:90}} }, { $sort:{"all_price":-1} }, ]) { "_id": ObjectId("5b743d8c2c327f8d1b360540"), "trade_no": "111", "all_price": 100, "items": [ { "_id": ObjectId("5b743d9c2c327f8d1b360543"), "order_id": "1", "title": "商品鼠標 1", "price": 50, "num": 1 }, { "_id": ObjectId("5b743da12c327f8d1b360544"), "order_id": "1", "title": "商品鍵盤 2", "price": 50, "num": 1 }, { "_id": ObjectId("5b74f457089f78dc8f0a4f3b"), "order_id": "1", "title": "商 品鍵盤 3", "price": 0, "num": 1 } ] } { "_id": ObjectId("5b743d902c327f8d1b360541"), "trade_no": "222", "all_price": 90, "items": [ { "_id": ObjectId("5b743da52c327f8d1b360545"), "order_id": "2", "title": "牛奶", "price": 50, "num": 1 }, { "_id": ObjectId("5b743da92c327f8d1b360546"), "order_id": "2", "title": "酸奶", "price": 40, "num": 1 } ] } ```