Mongoose查询帮助：对嵌套数组进行分页，排序和限制

Question

我正在聊聊Mongoose模型，下面是示例数据。如果仍然不清楚，请回答我的问题。非常感谢任何帮助。

        { 
            "_id" : ObjectId("5745910831a1sd58d070a8faa"), 
            "messages" : [
                {
                    "user" : "user1", 
                    "message" : "How are you user1?", 
                    "readInd" : "N", 
                    "createDate" : ISODate("2016-05-25T11:36:00.468+0000"), 
                    "_id" : ObjectId("5745912c31a1c58d070a904d")
                }, 
                {
                    "user" : "user1", 
                    "message" : "Hello user1", 
                    "readInd" : "N", 
                    "createDate" : ISODate("2016-05-25T11:38:53.893+0000"), 
                    "_id" : ObjectId("5745912531a1c58d070a902e")
                }
            ], 
            "createDate" : ISODate("2016-05-25T11:35:20.534+0000"), 
            "users" : [
                "57450b4506561ff5052f0a66", 
                "57450d8108d8d22c06cf138f"
            ], 
            "__v" : NumberInt(0)
        },
        { 
            "_id" : ObjectId("57458e9331a1c58d070a8e30"), 
            "messages" : [
                {
                    "user" : "user2", 
                    "message" : "How are you user2", 
                    "readInd" : "N", 
                    "createDate" : ISODate("2016-05-25T11:46:03.240+0000"), 
                    "_id" : ObjectId("574590f331a1c58d070a8ede")
                }, 
                {
                    "user" : "user2", 
                    "message" : "Hello user2", 
                    "readInd" : "N", 
                    "createDate" : ISODate("2016-05-25T11:48:53.925+0000"), 
                    "_id" : ObjectId("574590e931a1c58d070a8eab")
                }
            ], 
            "createDate" : ISODate("2016-05-25T11:35:20.534+0000"), 
            "users" : [
                "5745149e3aaab38706c00b64", 
                "57450d8108d8d22c06cf138f"
            ], 
            "__v" : NumberInt(0)
        }
        { 
            "_id" : ObjectId("5745910831a1c58d070a8faa"), 
            "messages" : [
                {
                    "user" : "user3", 
                    "message" : "How are you user3?", 
                    "readInd" : "N", 
                    "createDate" : ISODate("2016-05-25T11:56:00.468+0000"), 
                    "_id" : ObjectId("5745912c31a1c58d070a904d")
                }, 
                {
                    "user" : "user3", 
                    "message" : "Hello user3", 
                    "readInd" : "N", 
                    "createDate" : ISODate("2016-05-25T11:58:53.893+0000"), 
                    "_id" : ObjectId("5745912531a1c58d070a902e")
                }
            ], 
            "createDate" : ISODate("2016-05-25T11:35:20.534+0000"), 
            "users" : [
                "57450b4506561ff5052f0a66", 
                "57450d8108d8d22c06cf138f"
            ], 
            "__v" : NumberInt(0)
        },
        { 
            "_id" : ObjectId("5745910831a1c58d070a8faa"), 
            "messages" : [
                {
                    "user" : "user4", 
                    "message" : "How are you user4?", 
                    "readInd" : "N", 
                    "createDate" : ISODate("2016-05-25T11:66:00.468+0000"), 
                    "_id" : ObjectId("5745912c31a1c58d070a904d")
                }, 
                {
                    "user" : "user4", 
                    "message" : "Hello user4", 
                    "readInd" : "N", 
                    "createDate" : ISODate("2016-05-25T11:68:53.893+0000"), 
                    "_id" : ObjectId("5745912531a1c58d070a902e")
                }
            ], 
            "createDate" : ISODate("2016-05-25T11:35:20.534+0000"), 
            "users" : [
                "57450b4506561ff5052f0a66", 
                "57450d8108d8d22c06cf138f"
            ], 
            "__v" : NumberInt(0)
        }

下面是解释：

1. user1分别于11:36和11:38发送了2条消息
2. user2分别于11:46和11:48发送了2条消息
3. user3分别于11:56和11:58发送了2条消息
4. user4分别于11:66和11:68发送了2条消息

我的预期结果是：

分页/限制标准：

1. 每页显示2条记录。
2. 仅显示基于用户的最新消息。

示例输出：

第1页：

   "user" : "57450d8108d8d22c06cf138f",              
   "message" : "How are you user4?"

   "user" : "57450d8108d8d22c06cf138f", 
   "message" : "How are you user3?"

第2页：

   "user" : "57450d8108d8d22c06cf138f", 
   "message" : "How are you user2"

   "user" : "57450d8108d8d22c06cf138f", 
   "message" : "How are you user1?"

Answer 1

尝试这种查询方式，这对你有帮助

查询第一页

db.getCollection('message').aggregate( [ { $match : { user : "57450d8108d8d22c06cf138f" } },
{ $unwind : "$messages" } ,
{ $sort : { 'messages.createDate' : -1} },
 { $limit : 2 },
 { $project : { _id: 0,'message':'$messages.message','user':'$messages.user'} } ])

查询下一页

db.getCollection('message').aggregate( [ { $match : { user : "57450d8108d8d22c06cf138f" } },
    { $unwind : "$messages" } ,
    { $sort : { 'messages.createDate' : -1} },
     { $limit : 2 },{ $skip : 2 }
     { $project : { _id: 0,'message':'$messages.message','user':'$messages.user'} } ])