Advanced mongoose query operations

The convenience of Mongoose operation set is indeed not general, but it is mainly because you design the set in reference, however, it is a little troublesome for Mongoose to limit and identify the combination of sets when using ref to associate a set. But it doesn't matter. It's easy to use.

1. usage of the ref associated document in mongoose

2. query related documents by populate in mongoose

3. query to obtain a single set in the array

For example, there is a set:

{"_ Id": 11111, "Im": {"usergroup": [{"name": "friend list-2", "level": 1, "_ id": "53c4820263256dc316e98727", "list": [{"_ User": {"nickname": "mengmengfeiyang-2", "_ id": 22222, "icon": "/default/heads/2.png" }}, {" _ User ": NULL },{" _ User ": NULL },{" _ User ": null },{ "_ User": NULL },{ "_ User": NULL}] },{ "_ id": "53c488bf95ad1de01756db88", "name ": "Test usergroup", "level": 1, "list": []}

The above _ User indicates the associated document. If you only want to get one of the usergroup, and the condition is {'usergroup. $ ': 1}, you can get a code that meets the conditions as follows:

 UserModel.User.findOne({_id:11111,‘im.usergroup._id‘:‘53c488bf95ad1de01756db88‘},{‘im.usergroup.$‘:1})        .populate(‘im.usergroup.list._user‘,{icon:1,nickname:1,_id:1,name:1,remark:1})        .exec(function(err, ug){            cb(err,ug);        })

The above usermodel. user is the user's Mongoose Model

After query, you can get the following information:

{    "_id": 11111,    "im": {        "usergroup": [            {                "_id": "53c488bf95ad1de01756db88",                "name": "test usergroup",                "level": 1,                "list": []            }        ]    }}