Mongodb:查询文档中的数组元素 [英] Mongodb: Querying array elements within a document

问题描述

我有一个要查询的收藏集，如下所示:

I have a collection I'd like to query as follows:

• 返回所有文档
• 最多2条评论(例如，一片，0条，1条或2条评论)
• 所有评论的观看次数必须大于10

似乎我需要创建一个函数来分别评估每个文档，但是目前尚不清楚该如何完成，特别是考虑到我要进行切片并返回最多n个符合该条件的项目.

It seems like I need to create a function to evaluate each document individually, but it's not clear how that's done, particularly given I want to do a slice and return up to n items matching that criteria.

示例架构:

{
    title: "One",
    comments: [
        {
            title: "comment1",
            views: 9
        },
        {
            title: "comment2",
            views: 10
        },
        {
            title: "comment3",
            views: 11
        },
        {
            title: "comment4",
            views: 12
        },
    ]
}

我想做类似的事情:

db.collection.find({"comments.views": {$gt: 10}}, {comments:{$slice: 2}})

但是，这将返回任何带有> 10个视图的注释的文档，然后切片2个注释...我想返回那些包含> 10个项目的注释.我不能在客户端上执行此操作，而使用$ slice而不丢失一些注释，因此我需要在数据库上执行此操作.有想法吗?

But this returns any document with a comment with > 10 views, and then slices 2 comments... I want to return on those comments which have > 10 items. I cannot do it on the client AND use $slice without losing some comments, so I need to do it on the DB. Thoughts?

推荐答案

但是这将返回带有注释的任何文档，这些文档具有> 10个视图，然后 切片2条评论

But this returns any document with a comment with > 10 views, and then slices 2 comments

这是过滤多级嵌入式文档的行为，通常匹配的过滤器将返回整个文档，而不是子集.

This is the behavior of filtering multi level embedded document, normally the matching filter would return the whole document, not the subsets.

通常使用位置运算符$来匹配更新中的子文档.但是该功能尚未在返回说明符中实现.

Usually positional operator $ used to match the sub documents in updates. But the feature is not yet implemented in return specifiers.

mongo中已经存在一个未解决的问题，该支持在字段中返回位置($)运算符以返回指定值 r. (如果您确实需要此功能，请登录以投票)

There is an outstanding issue already in mongo Support for positional ($) operator in fields to return specifier. (Please login to vote if you really needed the feature)

所以您必须处理

• 最多2条评论(例如，一片，0条，1条或2条评论)

通过所有集合循环遍历您的应用程序.

part in your application by loop through all collections.

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