FluentQuery ignores .project(...)

[gusega]

Hi all,

I downloaded main version of spring data (commit sha: 12b5e82)

I enabled query logging and run UserRepositoryTests#findByFluentSpecificationWithSimplePropertyPathsDoesntLoadUnrequestedPaths test with maven profiles hibernate-62 and all-dbs:

In the logs I see the resulting query:

select u1_0.id,u1_0.DTYPE,u1_0.active,u1_0.city,u1_0.country,u1_0.streetName,u1_0.streetNo,
u1_0.age,u1_0.binaryData,u1_0.createdAt,u1_0.dateOfBirth,u1_0.emailAddress,u1_0.firstname,
u1_0.lastname,u1_0.manager_id,u1_0.secondary_email_address 
from SD_User u1_0 where cast(u1_0.firstname as varchar(2147483647)) like ?

I expect to see only u1_0.firstname in the select

The test queries data with

List<User> users = repository.findBy(userHasFirstnameLike("v"), q -> q.project("firstname").all());

FluentQuery#project(...) javadoc says: Define which properties or property paths to include in the query.

[mp911de]

JPA imposes quite a few limitations. We cannot select only a few properties when returning an entity. While this can work with Hibernate via multiselect and aliased selection items, JPA 3.2 deprecates multiselect and so this approach isn't usable.

We provide projection properties to JPA as fetchgraph so that joined properties can be selected/skipped when properties are declared.

Technically, we could use projection properties as input properties for DTO and interface projections but from a conceptional perspective, this would for DTO introduce a possibility of defining properties without ensuring that a matching constructor is present. For interface projections, we also select the entire entity (open projection) or selected properties (closed projection) so in both case we would introduce mechanisms that allow breaking functionality.

[mp911de]

Taking a step backward, what do you want to achieve with that setup and what problem are you trying to solve so that we better understand your context. One problem that can emerge from here is a partially hydrated entity that if saved, can wipe database information.

I have to admit that the test name is somewhat generalized, it actually tests if relations aren't loaded and not simple properties.

[gusega]

@mp911de my entity has a property whose value is a large json document. I only want database to return that json property when application queries a single entity.

When application queries multiple entities, I want database to not return that json property. The application then projects that entity (without json property) result onto Entity_Without_Json_Property.

My application calls repository.findBy(q -> q.as(Entity_Without_Json_Property.class)). The query to the database still queries json property. I added .project([all properties except the json property]). The query still contains json property.

[mp911de]

Care to post the Entity_Without_Json_Property structure? I assume that your use-case will be made available through #3654 that solves also #2327

[gusega]

@mp911de UserRepositoryTests#findByFluentSpecificationWithSortedInterfaceBasedProjection test from spring-data-jpa is very similar to what my program does:

List<UserProjectionInterfaceBased> users = repository.findBy(userHasFirstnameLike("v"),
				q -> q.as(UserProjectionInterfaceBased.class).sortBy(Sort.by("firstname")).all());

I added .project("firstname") to the fluent query. It had no effect on the resulting database query.