MongoDB小结20 - find【查询条件$size】
size可以获得指定数组长度的文档
db.user.find({"fruit":{"$size":3}},{"_id":0}) { "fruit" : [ "apple", "banana", "cherry" ] } { "fruit" : [ "apple", "banana", "pear" ] } { "fruit" : [ "apple", "watermelon", "pear" ] }