The two ways MongoDB uses subdocuments as query conditions

    {      "_id": ObjectId ("52fc6617e97feebe05000000"),      "age": +,      "level": numberint (+),      "name": "Name5" ,      "person": [        {          "level": 5,          "score": +,        "CCC": {"ccc3": "FFF3"          :] Level ": 7,          " score ": All,          " like ":" Music "        }      ],      " score ": Numberint,      " sex ":" Male "    }

Method One:

Db.testColl.find ({"Person.level": 7});d B.testcoll.find ({"PERSON.CCC.CCC3": 56});

　　

Can detect the results, that is, this method can be nested use!

Method two, using the $elemmatch operator

Db.testColl.find ({"person": {"$elemMatch": {"Level": 5}});

　　

We can find the results.

Db.testColl.find ({"person": {"$elemMatch": {"CCC": {"$elemMatch": {"ccc3": 56}}}});

　　

I can't find the results.

Db.testColl.find ({"person": {"$elemMatch": {"CCC": {"ccc3": "FFF3": +}}});d B.testcoll.find ({"person": {"$ Elemmatch ": {" ccc.ccc3 ": 56}});

　　

We can find the results.
This means that the second method cannot be nested.

The two ways MongoDB uses subdocuments as query conditions