查询内嵌文档和查询普通文档完全相同；
例如：
> db.post.find()
{ "_id" : ObjectId("54ace1394ba07ed75df68f90"), "name" : { "firstname" : "joe", "lastname" : "schome" }, "age" : 28 }
{ "_id" : ObjectId("54ace14a4ba07ed75df68f91"), "name" : { "firstname" : "snail", "lastname" : "yu" }, "age" : 29 }
{ "_id" : ObjectId("54ace18d4ba07ed75df68f92"), "name" : { "firstname" : "sunny", "lastname" : "wu" }, "age" : 26 }
> db.post.find({"name":{"firstname":"joe","lastname":"schome"}})
{ "_id" : ObjectId("54ace1394ba07ed75df68f90"), "name" : { "firstname" : "joe", "lastname" : "schome" }, "age" : 28 } >
查询内嵌文档必须精确匹配，如果顺序错了也是查询不到的；
我们可以改成”.”的模式来查询内嵌的文档，这样无需精确匹配，也无关顺序；
例如：
> db.post.find({"name.firstname":"joe"})
{ "_id" : ObjectId("54ace1394ba07ed75df68f90"), "name" : { "firstname" : "joe", "lastname" : "schome" }, "age" : 28 }
>
