Mock Projection Result Spring Data JPA

Question

I am using spring data jpa in my spring boot project.

I am firing an JPQL query and using an projection to store the result of query. My Projection :

public interface VeryBasicProjection {
    String getTitle();
    String getUrl();
}

My service calling this projection :

public List<VeryBasicDTO> getLatestData(int limit){

        // Pageable for Limit
        Pageable pageable = new PageRequest(0, limit);

        // Get Data from DB
        List<VeryBasicProjection> latestData = tableRepository.getLatestData("live", 2,pageable);
        List<VeryBasicDTO> responseDTO = new ArrayList<>();

        // Map Projection to DTO
        for(VeryBasicProjection veryBasicProjection : latestData){
            VeryBasicDTO veryBasicDTO = new VeryBasicDTO();
            veryBasicDTO.buildDTO(veryBasicProjection);
            responseDTO.add(veryBasicDTO);
        }

        return responseDTO;
    }

Now i want to test this service using Mockito(Unit Test Case) I am mocking the call to repository using when and thenReturn.

My question is how do I mock the result of repository? What should be in thenReturn? I mean how do I create instance of projection and setData to it?

Answer 1

If you want to create an instance of your projection without creating a class implementing the interface, you can use SpelAwareProxyProjectionFactory.

import org.springframework.data.projection.ProjectionFactory;
import org.springframework.data.projection.SpelAwareProxyProjectionFactory;

...
ProjectionFactory factory = new SpelAwareProxyProjectionFactory();
VeryBasicProjection projection = factory.createProjection(VeryBasicProjection.class);
projection.setTitle("theTitle");
projection.setUrl("theUrl");

You also need to add setters in your projection:

public interface VeryBasicProjection {
    String getTitle();
    String getUrl();
    void setTitle(String title);
    void setUrl(String url);
}

Source: https://github.com/spring-projects/spring-data-examples/blob/master/rest/projections/src/test/java/example/springdata/rest/projections/SimpleProjectionTests.java

Answer 2

This is the simplest way to mock projections in TEST

VeryBasicProjection VeryBasicProjection = new VeryBasicProjection() {
   String getTitle() {
    return "Title";
   }

    String getUrl() {
      return "url";
    }
}