Mongodb Java driver use limit in aggregation query

Question

Problem

Query is working fine but not limit and skip, it is fetching all records at once.

Kindly suggest what I am doing wrong.

MongoDB Collection

 {  
      "_id" : ObjectId("559666c4e4b07a176940c94f"),     
      "postId" : "559542b1e4b0108c9b6f390e",    
     "user" : {         
                 "userId" : "5596598ce4b07a176940c943",         
                 "displayName" : "User1",       
                 "username" : "user1",      
                 "image" : ""   
      },    
      "postFor" : {         
                     "type": "none",
                      "typeId" : ""     
      },    
     "actionType" : "like",     
     "isActive" : 1,
     "createdDate" : ISODate("2015-07-03T10:41:07.575Z"),   
     "updatedDate" : ISODate("2015-07-03T10:41:07.575Z") 
}

Java driver Query

 Aggregation aggregation = newAggregation(                                

      match(Criteria.where("isActive").is(1).and("user.userId").in(feedUsers)),
      group("postId")
      .last("postId").as("postId")
      .last("postFor").as("postFor")
      .last("actionType").as("actionType")
      .last("isActive").as("isActive")
      .last("user").as("user")
      .last("createdDate").as("createdDate")
      .last("updatedDate").as("updatedDate"),
      sort(Sort.Direction.DESC, "createdDate")
    );
aggregation.skip( skip );
aggregation.limit( limit );
AggregationResults<UserFeedAggregation> groupResults =
mongoOps.aggregate(aggregation, SocialActionsTrail.class, UserFeedAggregation.class);
return groupResults.getMappedResults();

Thanks

Blakes Seven · Accepted Answer · 2015-07-03 13:00:21Z

8

Aggregation pipelines are "sequential" in operation. These are not like .find() operations where .sort() .limit() .skip() are "modifiers" to the query operation:

Aggregation aggregation = newAggregation(                               
    match(Criteria.where("isActive")
        .is(1).and("user.userId").in(feedUsers)),
    group("postId")
        .last("postId").as("postId")
        .last("postFor").as("postFor")
        .last("actionType").as("actionType")
        .last("isActive").as("isActive")
        .last("user").as("user")
        .last("createdDate").as("createdDate")
        .last("updatedDate").as("updatedDate"),
    sort(Sort.Direction.DESC, "createdDate"),
    skip( skip ),
    limit( limit )
);

Unless you define the operations in "sequence" then the pipeline does not know the order of execution. So define the pipeline as a whole.

A basic example:

Aggregation aggregation = newAggregation(
    group("postId"),
    skip(1),
    limit(1)
);

System.out.println(aggregation)

Outputs a perfect pipeline:

{ 
    "aggregate" : "__collection__" ,
    "pipeline" : [ 
        { "$group" : { "_id" : "$postId" } },
        { "$skip" : 1 },
        { "$limit" : 1 }
    ]
}

See $skip and $limit in the core documentation.

edited Jul 3, 2015 at 13:00

answered Jul 3, 2015 at 12:32

Blakes Seven

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7 Comments

Rajnish katiyar - SIPL Over a year ago

I tried it. I got error - The method skip(int) is undefined

Blakes Seven Over a year ago

@Rajnishkatiyar-SIPL So the variable for skip is undefined! Surely that should be a clear error. The point I am making is that your basic calling sequence was incorrect.

Rajnish katiyar - SIPL Over a year ago

I can assure you that is not an issue because I have tried like this also- skip( 0 ), limit( 5 )

Blakes Seven Over a year ago

@Rajnishkatiyar-SIPL You need to take more than a few seconds to response. Run the code. .skip(0) does not result in "undefined".

Ajay Kurmi Over a year ago

@BlakesSeven you are right in that, but mongodb java spring driver dont have skip and limit method like sort and group. I also have same problem with skip and limit function with aggregation.

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