mongodb 访问子文档 [英] mongodb accessing subdocuments

问题描述

我有一个与下面提到的非常相似的集合(用户).

I have a collection (users) which looks very much the same as mentioned below.

db.users.find().pretty();
{
        "_id" : ObjectId("5773fc2826e0b6cf532569ca"),
        "user" : {
                "login" : "tester"
        }
}
{
        "_id" : ObjectId("5773fd6426e0b6cf532569cb"),
        "user" : {
                "login" : "tester",
                "name" : "anil"
        }
}

当我这样做

> db.users.find({"user":{"login":"tester"}});

我得到了这个结果

{ "_id" : ObjectId("5773fc2826e0b6cf532569ca"), "user" : { "login" : "tester" } }

但是当我在下面做时，我没有得到任何记录.

However when I do below, I get no records.

db.users.find({"user":{"name":"anil"}});

>所以我的问题是为什么第二个查询没有返回响应?

> so my question is why does the second query returns no response ?

另外，根据上面的例子，我什至怀疑这是否是访问子文档的正确方法?

Also, based on the examples above, I am even doubting if this is the correct way to access subdocuments ?

不应该通过 .notation 访问子文档.像下面这样?(在这种情况下，我在两种情况下都得到了正确的输出)

Shouldn't the subdocuments be accessed via .notation. Something like below ? (in which case I get the correct output in both the cases)

db.users.find({"user.login":"tester"});
{ "_id" : ObjectId("5773fc2826e0b6cf532569ca"), "user" : { "login" : "tester" } }
{ "_id" : ObjectId("5773fd6426e0b6cf532569cb"), "user" : { "login" : "tester", "name" : "anil" } }

和

> db.users.find({"user.name":"anil"});
{ "_id" : ObjectId("5773fd6426e0b6cf532569cb"), "user" : { "login" : "tester", "name" : "anil" } }
>

推荐答案

另外，根据上面的例子，我什至怀疑这是否是访问子文档的正确方法?

Also, based on the examples above, I am even doubting if this is the correct way to access subdocuments ?

这实际上不是.第一个查询，db.users.find({"user":{"login":"tester"}});，意味着你正在寻找一个user 完全等于 {"login":"tester"} 对象，而不是具有 login 字段的用户等于 tester.有一个文档与该条件匹配，并且该文档实际作为查询结果返回.

This is not actually. The first query, db.users.find({"user":{"login":"tester"}});, means that you're looking for a user that equals to {"login":"tester"} object completely, not a user with login field equals to tester. There is one document that matches with that criteria and that document actually returned as the query result.

同样，第二个查询 db.users.find({"user":{"name":"anil"}}); 表示您正在寻找一个 user 完全等于 {"name":"anil"} 对象.没有这样的user.有一个文档与您的查询部分匹配，但这还不够.

Likewise, the second query, db.users.find({"user":{"name":"anil"}});, means that you're looking for a user that equals to {"name":"anil"} object completely. There is no such user. There is one document that matches with your query partially but it's not enough.

如果您正在寻找 name 等于 anil 的 user，请使用 Dot Notation 访问子文档，就像您在第二组查询中所做的那样.

If you're looking for a user with name equals to anil, use Dot Notation to access the sub-document, as you did in your second group of queries.

不应该通过 .notation 访问子文档.就像是以下 ?(在这种情况下，我在两种情况下都得到了正确的输出)

Shouldn't the subdocuments be accessed via .notation. Something like below ? (in which case I get the correct output in both the cases)

是的.这是正确的方法.

Yes. this is the correct way.

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