Spring Data Mongo Template - Counting an array

Question

Mongo document:

{
    "_id" : "1",
    "array" : [
        {
            "item" : "item"
        }, 
        {
            "item" : "item"
        }
    ]
}

My mongo shell query looks like so:

db.getCollection('collectionName').aggregate(
    {$match: { _id: "1"}},
    {$project: { count: { $size:"$array" }}}
)

Is there anyway to implement this using the Mongo Template from Spring?

So far I have this:

MatchOperation match = new MatchOperation(Criteria.where("_id").is("1"));
ProjectionOperation project = new ProjectionOperation();
Aggregation aggregate = Aggregation.newAggregation(match, project);
mongoTemplate.aggregate(aggregate, collectionName, Integer.class);

I think I am only missing the project logic but I'm not sure if it is possible to do $size or equivalent here.

moffeltje · Accepted Answer · 2022-06-22 16:05:29Z

6

It's quite possible, the $size operator is supported (see DATAMONGO-979 and its implementation here). Your implementation could follow this example:

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

Aggregation agg = new Aggregation(
    match(where("_id").is("1")), //  
    project() //
        .and("array") //
        .size() //
        .as("count")
);

AggregationResults<IntegerCount> results = mongoTemplate.aggregate(
    agg, collectionName, Integer.class
);
List<IntegerCount> intCount = results.getMappedResults();

edited Jun 22, 2022 at 16:05

moffeltje

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answered Jun 14, 2016 at 13:41

chridam

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3 Comments

dragonalvaro Over a year ago

That 'where' is now Criteria.where( ... )

Meeresgott Over a year ago

Where does the IntegerCount came form? Is this only a POJO with attributes _id and count ?

takanuva15 Over a year ago

Note: if you just want the int count so you can return it from a method, you can get it out with this results.getUniqueMappedResult().getInteger("count"). (You must change IntegerCount.class above to org.bson.Document.class)

notionquest · Accepted Answer · 2016-06-14 13:54:34Z

Please find below the sample code. You can change it accordingly for your requirement with collection name, collection name class and array field name.

    MatchOperation match = new MatchOperation(Criteria.where("_id").is("1"));
    Aggregation aggregate = Aggregation.newAggregation(match, Aggregation.project().and("array").project("size").as("count"));

    AggregationResults<CollectionNameClass> aggregateResult = mongoOperations.aggregate(aggregate, "collectionName", <CollectionNameClass>.class);

    if (aggregateResult!=null) {
        //You can find the "count" as an attrribute inside "result" key
        System.out.println("Output ====>" + aggregateResult.getRawResults().get("result"));
        System.out.println("Output ====>" + aggregateResult.getRawResults().toMap());
    }

Sample output:-

Output ====>[ { "_id" : "3ea8e671-1e64-4cde-bd78-5980049a772b" , "count" : 47}]
Output ====>{serverUsed=127.0.0.1:27017, waitedMS=0, result=[ { "_id" : "3ea8e671-1e64-4cde-bd78-5980049a772b" , "count" : 47}], ok=1.0}

user1211 · Accepted Answer · 2016-06-14 13:41:58Z

0

You can write query as

 Aggregation aggregate = Aggregation.newAggregation(Aggregation.match(Criteria.where("_id").is(1)),
            Aggregation.project().and("array").size().as("count")); mongoTemplate.aggregate(aggregate, collectionName, Integer.class);

It will execute the following query { "aggregate" : "collectionName" , "pipeline" : [ { "$match" : { "_id" : 1}} , { "$project" : { "count" : { "$size" : [ "$array"]}}}]}

answered Jun 14, 2016 at 13:41

user1211

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