Question

我认为我错过了MongoDB Aggregate Pipeline知识的一个关键部分，以便接近我想要做的事情。

这是我的数据：

[
   {frameId: <some unique guid>, videoSessionId: 1, subject: "John", "createdBy": "personA", "blurry": false},
   {frameId: <some unique guid>, videoSessionId: 1, subject: "John", "createdBy": "personA", "blurry": false},
   {frameId: <some unique guid>, videoSessionId: 1, subject: "John", "createdBy": "personA", "blurry": false},
   {frameId: <some unique guid>, videoSessionId: 2, subject: "John", "createdBy": "personA", "blurry": false},
   {frameId: <some unique guid>, videoSessionId: 3, subject: "John", "createdBy": "personB", "blurry": true},
   {frameId: <some unique guid>, videoSessionId: 3, subject: "John", "createdBy": "personB", "blurry": true},
   {frameId: <some unique guid>, videoSessionId: 3, subject: "John", "createdBy": "personB", "blurry": false},
   {frameId: <some unique guid>, videoSessionId: 3, subject: "John", "createdBy": "personB", "blurry": false},
   {frameId: <some unique guid>, videoSessionId: 4, subject: "Mary", "createdBy": "personB", "blurry": false},
   {frameId: <some unique guid>, videoSessionId: 4, subject: "Mary", "createdBy": "personB", "blurry": false},
   {frameId: <some unique guid>, videoSessionId: 5, subject: "Mary", "createdBy": "personB", "blurry": false},
   {frameId: <some unique guid>, videoSessionId: 5, subject: "Mary", "createdBy": "personB", "blurry": false},
   {frameId: <some unique guid>, videoSessionId: 6, subject: "Mary", "createdBy": "personB", "blurry": false},
   {frameId: <some unique guid>, videoSessionId: 6, subject: "Mary", "createdBy": "personB", "blurry": false},
   {frameId: <some unique guid>, videoSessionId: 7, subject: "Mary", "createdBy": "personB", "blurry": false},
   {frameId: <some unique guid>, videoSessionId: 7, subject: "Mary", "createdBy": "personB", "blurry": false},
   {frameId: <some unique guid>, videoSessionId: 7, subject: "Mary", "createdBy": "personB", "blurry": false},
   {frameId: <some unique guid>, videoSessionId: 7, subject: "Mary", "createdBy": "personB", "blurry": false},
   {frameId: <some unique guid>, videoSessionId: 7, subject: "Mary", "createdBy": "personB", "blurry": false},
]

我想查询数据并收到：

[
       {frameId: <some unique guid>, videoSessionId: 3, subject: "John", "createdBy": "personB", "blurry": false},
       {frameId: <some unique guid>, videoSessionId: 3, subject: "John", "createdBy": "personB", "blurry": false},
       {frameId: <some unique guid>, videoSessionId: 4, subject: "Mary", "createdBy": "personB", "blurry": false},
       {frameId: <some unique guid>, videoSessionId: 4, subject: "Mary", "createdBy": "personB", "blurry": false},
       {frameId: <some unique guid>, videoSessionId: 5, subject: "Mary", "createdBy": "personB", "blurry": false},
       {frameId: <some unique guid>, videoSessionId: 5, subject: "Mary", "createdBy": "personB", "blurry": false},    
]

这是我想要的明文版本：

＆＃34;在personB创建的所有非模糊帧中，每个主题给我最多2个videoSessions。＆＃34;

更深一点：

以上查询的数据只包含一个videoSession的数据，因为John只有1个由personB创建的videoSession。
上述查询数据仅包含Mary的4个视频会话中的2个。虽然她有4个由personB创建并且不模糊的视频会话，但我们希望每个主题最多只能收集2个视频会话。

我目前正在解决这个问题，使用以下方法。这对我来说似乎效率低下，因为它需要查找，展开，替换root和另一个匹配。

$ match createdBy = personB and blurry = false
$ subject by subject和$ addToSet of videoSessionId获取videoSessionIds数组
一个$项目，它使用maxNumber的$ slice来限制每个主题的videoSessionIds
在同一个集合上通过videoSessionId进行$ lookup和$展开以填充原始数据
一个$ replaceRoot，因为$ unwind将它放入主题
另一个$ match for createdBy = personB和blurry = false - ＆gt;因为$ lookup和$ unwind给了我所有记录回来的特定videoSessionIds我发现我想要的。

MongoDB - 具有匹配的聚合和限制为分组字段的最大数量

0 个答案: