Projections doesn't work using data-repositories

[alesikov]

Hello,
Unfortunately any kind of projections doesn't work with data-repositories. It's probably caused by

spring-data-r2dbc/src/main/java/org/springframework/data/r2dbc/repository/query/AbstractR2dbcQuery.java

Line 136 in c3cb70f

return returnedType.isProjecting() ? returnedType.getDomainType() : returnedType.getReturnedType();

which could be probably solved by the following
return returnedType.isProjecting() ? returnedType.getReturnedType() : returnedType.getDomainType();

The above was tested locally and it worked, please kindly check.

[mp911de]

Can you provide a test case that shows that projections are broken? Our integration tests for projections pass so it would be good to know in which case projections don't work.

[alesikov]

My bad, forgot to mention that the issue is related to @Query-annotated methods which produce class-based projections.
Apparently the tests don't cover the scenario when projection has different field names than the entity
Managed to reproduce the same using integration tests you mentioned previously, the proposed fix still works. Please try testing against the following:

// Projection
@Value
static class NamedDTO {
    String doesntBelongToEntity;
}

// Repository method
@Query("SELECT name as doesnt_belong_to_entity FROM legoset")
Flux<NamedDTO> projectingWithQuery();

[mp911de]

DTO projections work actually on top of the repository entity type in the sense that DTO's are a subset of entity properties. Additional properties aren't really expected here.

The following code should explain the underlying assumptions:

class Person {
    @Column("fn")
    String firstName;
}

class PersonDto {
   String firstName;
}

Assuming the firstName property maps onto the fn column in your database, then a derived query would apply proper fieldname mapping:

Flux<PersonDto> findBy();

resulting in the SQL:

SELECT fn FROM person;

If we now translate that behavior to String-based queries, what would the select look like for:

@Query("SELECT … FROM person");
Flux<PersonDto> findBy();

Is it SELECT fn FROM person or would it rather be SELECT fn AS firstName FROM person?

[mp911de]

Likely, using the domaintype -> DTO for derived query processing and reading directly into the DTO for string-based queries is a good middleground as for string queries the type declaration and @Query are pretty close. For derived queries, you typically don't have much control over the projected queries.

[mp911de]

That change is in place now.

[alesikov]

Thank you for the amazing project