Random documents from MongoDB using spring-data

Question

I\'m able to do it by using this mongodb native query:

db.books.aggregate(
   [ { $sample: { size: 15 } } ]
)

But how to do it in spr

Answer 1

Update:

Starting with v2.0 of Spring Data you can do this:

SampleOperation matchStage = Aggregation.sample(5);
Aggregation aggregation = Aggregation.newAggregation(sampleStage);
AggregationResults output = mongoTemplate.aggregate(aggregation, "collectionName", OutType.class);

---

Original answer:

Abstraction layers like spring-mongo are always going to lag way behind server released features. So you are best off contructing the BSON document structure for the pipeline stage yourself.

Implement in a custom class:

public class CustomAggregationOperation implements AggregationOperation {
    private DBObject operation;

    public CustomAggregationOperation (DBObject operation) {
        this.operation = operation;
    }

    @Override
    public DBObject toDBObject(AggregationOperationContext context) {
        return context.getMappedObject(operation);
    }
}

And then use in your code:

Aggregation aggregation = newAggregation(
    new CutomAggregationOperation(
        new BasicDBObject(
            "$sample",
            new BasicDBObject( "size", 15 )
        )
    )
);

Since this implements AggregationOperation this works well with the exising pipeline operation helper methods. i.e:

Aggregation aggregation = newAggregation(
    // custom pipeline stage
    new CutomAggregationOperation(
        new BasicDBObject(
            "$sample",
            new BasicDBObject( "size", 15 )
        )
    ),
    // Standard match pipeline stage
    match(
        Criteria.where("myDate")
            .gte(new Date(new Long("949384052490")))
            .lte(new Date(new Long("1448257684431")))
    )
);

So again, everything is just a BSON Object at the end of the day. It's just a matter of having an interface wrapper so that the class methods in spring-mongo interpret the result and get your defined BSON Object correctly.