如何在 mongodb 集合上合并子文档（作为数组）答案

【问题标题】：How I can merge sub-document (as array) on mongodb collection如何在 mongodb 集合上合并子文档（作为数组）
【发布时间】：2014-03-06 10:26:44
【问题描述】：

你好，我有一个收藏：

{
    "_id" : ObjectId("508d27069cc1ae293b36928d"),
    "title" : "This is the title",
    "body" : "This is the body text.",
    "created_date" : ISODate("2012-10-28T12:41:39.110Z"),
    "comments" : [
        {
            "subject" : "This is coment 1",
            "body" : "This is the body of comment 1.",
            "author_id" : ObjectId("508d345f9cc1ae293b369296"),
            "created_date" : ISODate("2012-10-28T13:34:23.929Z")
        },
        {
            "subject" : "This is coment 2",
            "body" : "This is the body of comment 2.",
            "author_id" : ObjectId("508d34739cc1ae293b369297"),
            "created_date" : ISODate("2012-10-28T13:34:43.192Z")
        },
        {
            "subject" : "This is coment 3",
            "body" : "This is the body of comment 3.",
            "author_id" : ObjectId("508d34839cc1ae293b369298"),
            "created_date" : ISODate("2012-10-28T13:34:59.336Z")
        }
    ]
}

所以，在仪表板的一页上，我想查看所有 cmets，我该怎么做？如何获取单个集合中每个帖子的所有 cmets，如何识别每个评论（用于编辑或删除）？

UPD1：

这是来自帖子集合的文档。我想得到这样的东西：

[
    ...,
    {
         "_generated_id_for_identify": [What the data?],
         "subject" : "This is coment 1",
         "body" : "This is the body of comment 1.",
         "author_id" : ObjectId("508d345f9cc1ae293b369296"),
         "created_date" : ISODate("2012-10-28T13:34:23.929Z")
    },
    {
         "_generated_id_for_identify": [What the data?],
         "subject" : "This is coment 2",
         "body" : "This is the body of comment 2.",
         "author_id" : ObjectId("508d34739cc1ae293b369297"),
         "created_date" : ISODate("2012-10-28T13:34:43.192Z")
    },
    ...,
    {
         "_generated_id_for_identify": [What the data?],
         "subject" : "This is coment N",
         "body" : "This is the body of comment N.",
         "author_id" : ObjectId("508d34839cc1ae293b369298"),
         "created_date" : ISODate("2012-10-28T13:34:59.336Z")
    },
    ...
]

【问题讨论】：

对不起，您的问题不是很清楚。这是您的收藏现在的样子，还是您想要的样子？

标签： mongodb collections nosql-aggregation

【解决方案1】：

在帖子集合中聚合并通过“_id”匹配，然后在 cmets 和 proyection 中使用 unwind，您可以在 results 键中获得新的 cmets 集合。

db.posts.aggregate([
                   {$match:{_id:ObjectId("508d27069cc1ae293b36928d")}}, 
                   {$unwind:"$comments"}, 
                   {$project:{
                              "_id":{id:"$_id",dt:"$comments.created_date"},
                            subject:"$comments.subject",
                               body:"$comments.body",
                         "autor_id":"$comments.author_id",
                     "created_date":"$comments.created_date"}} ]).result

但是通过匹配posts._id 的简单查询，您可以获得post.cmets

【讨论】：