CODEWITHSUNDEEP
spring-data-mongodb
Dennis Nijssen
Dennis Nijssen

Reputation: 175

Spring Data MongoDB reactive distinct not working

Consider the following dependency:

I'm having a collection of which I need to retrieve distinct values. However when I'm using a query method to retrieve a Flux of distinct values, it is not working. I defined the following query method, using a closed projection IdentifierOnly:

@Repository
public interface FooBarRepository extends ReactiveCrudRepository<FooBar, String> {

    Flux<IdentifierOnly> findDistinctByFooAndBar(String foo, String bar);
}

The document / collection class:

@Document
public class FooBar {

    private String identifier; // not unique
    private String foo;
    private String bar;
    // extra fields

    // getters and setters
}

The closed projection:

public interface IdentifierOnly {

    getIdentifier();
}

However the query that is executed and logged by the ReactiveMongoTemplate is the following: find using query: { "foo" : "xxxx", "bar" : "yyyy" } fields: Document{{identifier=1}} for class: class org.example.models.FooBar in collection: fooBar and is not returning any results in a distinct way, because it contains duplicates.

What am I doing wrong? How can I retrieve distinct values (identifiers) based on a specific query?

Upvotes: 0

Views: 955

Answers (1)

mp911de
mp911de

Reputation: 18119

TL;DR

That does not work (yet). I filed DATAMONGO-1985 to investigate how we can integrate distinct queries.

Explanation

MongoDB provides a distinct operation that requires exactly one field for retrieving distinct values. This operation is available on the Template API but not through the repository API. From a repository perspective, there's actually no possibility to specify the field which should be used for a distinct operation.

The code above forms an interesting case which uses all ingredients (distinct keyword, closed projection with a single field) that would be necessary to derive a distinct query.

Upvotes: 2

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