How to Limit Query Results with Annotations in Spring Data JPA?

setMaxResults Annotation for Spring-Data-JPA

Spring-Data-JPA, a powerful JPA repository abstraction library, simplifies data access in Spring-based Java applications. However, setting the maximum number of results returned by a query using annotations has been a challenge.

Spring Data JPA 1.7.0 (Evans Release Train) Solution

In Spring Data JPA 1.7.0 and later, the situation has improved. You can now use the Top and First keywords to restrict query results. For instance:

findTop10ByLastnameOrderByFirstnameAsc(String lastname);

Spring Data will automatically limit the number of returned results to the specified number (defaulting to 1 if omitted). Ordering of the results becomes crucial, either through an OrderBy clause or a Sort parameter in the method.

Prior to Spring Data JPA 1.7.0

Before this enhancement, retrieving data slices required the use of pagination. Spring Data employs a Pageable interface for pagination requests and a Page abstraction for result handling.

Implement the repository interface as follows:

public interface UserRepository extends Repository<User, Long> {

  List<User> findByUsername(String username, Pageable pageable);
}

Use the interface to obtain the results:

Pageable topTen = new PageRequest(0, 10);
List<User> result = repository.findByUsername("Matthews", topTen);

If context information is required, use Page as the return type:

public interface UserRepository extends Repository<User, Long> {

  Page<User> findByUsername(String username, Pageable pageable);
}

The client code can utilize this information:

Pageable topTen = new PageRequest(0, 10);
Page<User> result = repository.findByUsername("Matthews", topTen);
Assert.assertThat(result.isFirstPage(), is(true));

Using Page as a return type triggers a count projection query execution to determine the total number of elements. Additionally, to guarantee stable results, always include sorting information in the PageRequest.

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