Spring Data MongoDB - aggregate with nested field projection

Question

How can I translate the following into a spring data java query?

db.messages.aggregate([
    {$lookup:{from: "images", localField: "imageId", foreignField: "_id", as: "image"}},
    {$unwind: "$image"},
    {$project: {"text": 1, "liked": {$gt: [{$size: {$setIntersection: ['$image.likers', ['2']]}}, 0]}}}
    ])

Messages:

{
  "_id": "1",
  "text": "hi",
  "imageId": "1"
}

Images:

{
  "_id": "1",
  "likers": ["1","2","3"]
}

Basically I am trying to add a new field called "liked" and it should be true if user X liked the message/image. — shayy
– shayy, Commented May 22, 2017 at 11:45

s7vr · Accepted Answer · 2017-05-22 15:10:28Z

2

You can try below aggregation in 3.4 mongo version with 1.10.3 Spring Mongo Version / 1.5.3 Spring Boot Version.

Shell Query for Reference

db.messages.aggregate(
 { "$lookup" : { "from" : "images" , "localField" : "imageId" , "foreignField" : "_id" , "as" : "image"}} ,
 { "$unwind" : "$image"} , 
  { "$project" : { "text" : 1 , "liked" : { "$in" : [ "2" , "$image.likers"]}}}
)

Spring Mongo Code:

import static org.springframework.data.mongodb.core.aggregation.Aggregation.*;
import static org.springframework.data.mongodb.core.aggregation.ArrayOperators.arrayOf;

Aggregation agg = newAggregation(
 lookup("images", "imageId", "_id", "image"), 
 unwind("image"), 
 project("text").and(arrayOf("image.likers").containsValue("2")).as("liked")
);

answered May 22, 2017 at 15:10

s7vr

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3 Comments

Sachin Over a year ago

What is arrayOf here?

s7vr Over a year ago

@Sachin arrayOf is a static factory method to get reference to array operator factory and you can then perform operations on array. One such operations is containsValue which renders $in expression`. For complete list visit here

Sachin Over a year ago

as I mentioned on another question. can we use List of value in containsValue ?

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