Spring JPA: Using multiple projection on same query interface

Question

I am trying to use Spring JPA's projection to filter out unnecessary data from query result. However, I have multiple projections that will need to be used on the same interface method.

The problem is, I am trying to query data from the same method with a different returning object but java doesn't allowed this.

The query are auto generated by JPA based on method name, so I cannot make changes to method name.

Is there a alternative, other than creating a new interface, since I think it's a hassle and unnecessary

here is a sample code, of what I am trying to do.

Auto-Generated Query

public interface UserRepository extends CrudRepository<UserAccount, Long> {

    AuthenticateProjection getByUsername(String username);

    UserDetailsProjection getByUsername(String username);

}

Projections

public interface AuthenticateProjection {

    @Value("#{target.username}")
    String getUsername();

    @Value("#{target.credentail.token}")
    String getHashPassword();
}

public interface UserDetailsProjection {

    @Value("#{target.username}")
    String getUsername();

    @Value("#{target.firstname}")
    String getFirstName();

    @Value("#{target.lastname}")
    String getLastName();
}

Why are you wanting to "filter" the information--is this for returning from a controller, or for internal use? — chrylis -cautiouslyoptimistic-
– chrylis -cautiouslyoptimistic-, Commented Apr 11, 2017 at 17:55

XPLOT1ON · Accepted Answer · 2017-04-12 15:07:43Z

7

So I've managed to figure out how to use multiple projections with a single query.

<T> T getByUsername(String username, Class<T> projection)

This allows the method caller to specified the type of projection to be applied to the query.

To further improve this so it is less prone to error, I made a blank interface that the projection will have to extend in order to be able to insert class into the parameter.

public interface JPAProjection {
}

public interface UserRepository extends CrudRepository<UserAccount, Long> {
    <T extends JPAProjection > T getByUsername(String username, Class<? extends JPAProjection> projection);
}

Projection Interface

public interface UserDetailsProjection extends JPAProjection{
    @Value("#{target.username}")
    String getUsername();

    @Value("#{target.firstname}")
    String getFirstname();

    @Value("#{target.lastname}")
    String getLastname();
}

Then I can call the query method by

getByUsername("...", UserDetailsProjection.class)

answered Apr 12, 2017 at 15:07

XPLOT1ON

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2 Comments

Andrea Bevilacqua Over a year ago

I tried to use your same solution, but it does not work for me. In the Eclipse console I see an error:

Caused by: org.hibernate.hql.internal.ast.QuerySyntaxException: unexpected token: from near line 1, column 9 [select  from com.app.company.domain.organization.Organization as generatedAlias0 where generatedAlias0.deletedAt is null]

. Look at the "select" statement: there is not any column. Maybe did you have the same problem? It seems that the repository does not receive the correct projection type.....any idea? Thanks a lot!

XPLOT1ON Over a year ago

hmm this is odd. I did not have any problem. Would you mind attaching your impl? Pastebin maybe? @AndreaBevilacqua

user1056903 · Accepted Answer · 2020-01-24 00:09:53Z

3

Just add something between get (or e.g. find) and By starting with an upper case character. It is ignored in the query generation.

public interface UserRepository extends CrudRepository<UserAccount, Long> {

   AuthenticateProjection getByUsername(String username);

   UserDetailsProjection getAnotherByUsername(String username);

}

answered Jan 24, 2020 at 0:09

user1056903

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1 Comment

Fred Nobre Over a year ago

Best answer ! No code to write, you may only write the "mode" of the data you want to retrieve, like : getByUsername, getFullByUsername, getLightByUsername.

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