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Ever wanted to rewrite a query in Spring Data JPA?

Sometimes, no matter how many features you try to apply, it seems impossible to get Spring Data JPA to apply every thing you’d like to a query before it is sent to the EntityManager.

With 3.0.0-SNAPSHOT (and targeted for the next milestone release train of Spring Data), you now have the ability to get your hands on the query, right before it’s sent to the EntityManager and "rewrite" it. That is, you can make any alterations at the last moment.

Check it out below:

Example 1. Declare a QueryRewriter using @Query
public interface MyRepository extends JpaRepository<User, Long> {

    @Query(value = "select original_user_alias.* from SD_USER original_user_alias",
                    nativeQuery = true, queryRewriter = MyQueryRewriter.class) // (1)
    List<User> findByNativeQuery(String param);

    @Query(value = "select original_user_alias from User original_user_alias",
                   queryRewriter = MyQueryRewriter.class) // (2)
    List<User> findByNonNativeQuery(String param);
}
  1. This pure SQL query (thanks to nativeQuery) will get routed through yet-to-be-defined MyQueryRewriter before the query is invoked.

  2. This JPQL query will also get routed through the same MyQueryRewriter before it’s handed over to the EntityManager.

You can then write your own ticket, as shown below!

Example 2. Example QueryRewriter
public class MyQueryRewriter implements QueryRewriter {

    @Override
    public String rewrite(String query, Sort sort) {
        return query.replaceAll("original_user_alias", "rewritten_user_alias");
    }
}

Okay, this one is a tad contrived. We are basically changing the name of a particular query’s alias. But you can really do anything you can think of. This hook gives you a chance to change a little (or a lot!).

Just be sure to register an instance MyQueryRewriter in the application context. Whether you use one of Spring Framework’s @Component-based annotations, or you supply it through a @Bean method inside an @Configuration class, the choice is yours.

Warning
Your QueryRewriter is invoked after any and all checks have been performed by Spring Data JPA. You’re responsible for supplying a valid query to the EntityManager.

But wait…​there’s more!

While you can write your QueryRewriter as a separate bean, it’s also possible to put right inside the repository where it’s used!

Example 3. Repository that provides the QueryRewriter
public interface MyRepository extends JpaRepository<User, Long>,
                                   QueryRewriter { // (1)

    @Query(value = "select original_user_alias.* from SD_USER original_user_alias",
                   nativeQuery = true, queryRewriter = MyRepository.class) // (2)
    List<User> findByNativeQuery(String param);

    @Query(value = "select original_user_alias from User original_user_alias",
                   queryRewriter = MyRepository.class) // (3)
    List<User> findByNonNativeQuery(String param);

    @Override
    default String rewrite(String query, Sort sort) { // (4)
        return query.replaceAll("original_user_alias", "rewritten_user_alias");
    }
}
  1. Have your repository interface extend the QueryRewriter interface.

  2. Plug in the name of your repository into the native query’s @Query.queryRewriter entry.

  3. Plug in the name of your repository into the JPQL query’s @Query.queryRewriter entry.

  4. Override the rewrite(String,Sort) method and plugin a default value, and POOF you’re done!

Fair warning: it’s possible you may need more than one rewriter based on what exactly you’re doing.

Spring Data JPA supports not only Spring’s application context, but CDI-based environments.

Happy querying!

-Greg Turnquist

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