Mongodb 2.6.10 count（）aggregate（）

Question

在一个集合中，我需要找到拥有3个以上成员的组。显示组的名称和成员数。将结果数限制为4。

结构是{_id, Group_Name, Members:{First_Name, Second_Name, Age}}

我在相同的结构中使用了聚合和计数（也使用了限制），但结果并不像我预期的那样。

我该怎么做？我不需要年龄。

谢谢！ 例如：

    db.User_groups.find()
    {"_id":ObjectId("654765754575a7"),"Group_Name":"Group_AAA","Members":
    [{"_id":ObjectId("654646646554b8"),"First_Name":"John","Second_Name":
    "Potoshin","Age":34},{"_id":ObjectId("654765117575a8"),"First_Name":
    "Manfred","Second_Name":"Erassy","Age":40},{"id":
    ObjectId("656776432655t5"),"First_Name":"Dieter","Second_Name":
    "Koll","Age":45}],{"_id":ObjectId("654765333575a3"),"Group_Name":
    "Group_BBB","Members":[{"_id":ObjectId("654646222554b2"),
    "First_Name":"Jane","Second_Name":"Pilas","Age":43},
    {"_id":ObjectId("111765117575a1"),"First_Name":
    "Konrad","Second_Name":"Samir","Age":50}]}