Spring data mongodb query add boolean field if value exists in array

Question

I'm trying to query some data from mongoDb which contains likes array. Each like object holds user.id of liker.

I need an extra boolean field that says if document is liked by user or not. So I need isLiked to be true if user has liked the document.

Here is what I have done till now:

I used ConditionalOperators.Cond to check if likes.userId is equal to userId of visitor.

    @Override
public List<PostExtra> findPostsNearBy(double[] point, Distance distance, String thisUserId) {
    mongoTemplate.indexOps(CheckInEntity.class).ensureIndex(new GeospatialIndex("position"));

    ConditionalOperators.Cond conditionalOperators = new ConditionalOperators.ConditionalOperatorFactory(Criteria.where("likes.userId").is(thisUserId)).then(true).otherwise(false);


    Aggregation aggregation = Aggregation.newAggregation(
            Aggregation.geoNear(
                    locationBasedOperationHelper.findNear(point,distance)
                        .query(new Query(privacyConsideredOperationHelper.privacyConsideredQuery(userRelationsEntity)))
                    ,"distance"
            ),
            //Aggregation.unwind("likes"),
            Aggregation.project("user", "description").and(conditionalOperators).as("isLiked")
    );

    final AggregationResults<PostExtra> results =
            mongoTemplate.aggregate(aggregation, PostEntity.class, PostExtra.class);
    return results.getMappedResults();
}

if I remove the comment on Aggregation.unwind("likes") I can only get posts that this user has liked not those he hasn't.

I have seen the same matter here but I dont know whats the MontoTemplate code related to that? Also I have seen approaches with setIsSubset, still I dont know java implementation.

I'm using spring boot 2.0.4.RELEASE and spring-boot-starter-data-mongodb.

@Document(collection = EntityCollectionNames.POST_COLLECTION_NAME)
public class PostEntity{
    @Id
    private String id;
    @Field
    @DBRef
    @Indexed
    private UserEntity user;

    @GeoSpatialIndexed(type = GeoSpatialIndexType.GEO_2DSPHERE)
    @Field(value = "position")
    private Point position;

    @Field(value = "description")
    private String description;

    @Field
    private int likesCount;
    @Field
    private List<LikeEntity> likes;
}

Post Extra:

public class PostExtra extends PostEntity {
    private double distance;
    private boolean isLiked;
}

Like:

public class LikeEntity {
    @Field
    private String userId;
}

Sepehr GH · Accepted Answer · 2018-09-15 08:53:57Z

After some searching I found out to do it without using unwind I need to implement something like this to project isLiked field:

$cond:[
    {$gt:[
        {$size:
            {$setIntersection:["$likes.userId",userIdsToCheckIn]}
        },0]
    },true,false]

I tried to do it in spring like this:

    ConditionalOperators.Cond conditionalOperators = new ConditionalOperators.ConditionalOperatorFactory(
            ComparisonOperators.Gt.valueOf(
                ArrayOperators.Size.lengthOfArray(
                        SetOperators.SetIntersection.arrayAsSet("$likes.userId").intersects(????????)
                )
            ).greaterThanValue(0)
    ).then(true).otherwise(false);

But I didnt know what to pass to intersects() method and apparently Spring does not let you pass List or Array as that input. Then I found out I can implement my own AggregationExpressions and override toDocument() method.

So I came up with this and it worked:

ConditionalOperators.Cond conditionalOperators = new ConditionalOperators.ConditionalOperatorFactory(
                new AggregationExpression() {
                    @Override
                    public Document toDocument(AggregationOperationContext aggregationOperationContext) {
                        return Document.parse("{$gt:[{$size:{$setIntersection:[\"$likes.userId\",[\""+userId+"\"]]}},0]}");
                    }
                }
        ).then(true).otherwise(false);

Ofcourse I could add $cond to the implementation directly too.

I would still like to know if there are any spring solutions that does not contain mongodb queries directly for this.

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