Spring Data returning List<Object[]>

Question

I have this repository:

@Repository
public interface ProductRepository extends JpaRepository<Product, Long>{

@Query("SELECT p.textToSearch as text, count(*) as counter FROM Product p GROUP BY text_to_search ORDER BY counter DESC")
List<TopProductDTO> findTopProducts();
}

where the TopProductDTO class is:

public class TopProductDTO {

public TopProductDTO() {}

private String text;
private Integer counter;

// Getters and Setters are omited
}

But when I execute the code

List<TopProductDTO> topProducts = productRepository.findTopProducts();

It returns a

List<Object[]> insted a List<TopProductDTO>

As like each column is a index of the Object Array in the list... Wasn't it supposed to Spring Data binds the 'text' and 'counter' columns from query with the fields in TopProductDTO?

As result I got a this error in my Thymeleaf Template:

00:37:22.659 [http-nio-8080-exec-5] ERROR o.a.c.c.C.[.[.[.[dispatcherServlet] - Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.thymeleaf.exceptions.TemplateProcessingException: Exception evaluating SpringEL expression: "topProductDTO.text" (products/top:46)] with root cause
org.springframework.expression.spel.SpelEvaluationException: EL1008E:(pos 14): Property or field 'text' cannot be found on object of type 'java.lang.Object[]' - maybe not public?

I'm using Spring Boot 1.3.3 and Postgres 9.2

Answer 1

Try to use the constructor of your DTO.

Declare a new constructor

public TopProductDTO(String text, Integer count) {
    this.text = text;
    this.count = count;
}

In your query use the new Constructor

@Query("SELECT new TopProductDTO(p.textToSearch, count(id))FROM Product p GROUP BY text_to_search ORDER BY counter DESC")
List<TopProductDTO> findTopProducts();
}

Use the fully qualified name of your class.