Lazy Load in Hibernate

Question

I’m not getting Lazy Load to work in Spring.

I have the following structure.

//Livro.Java

@Entity
public class Livro {

    @JsonInclude(Include.NON_NULL)
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @NotEmpty(message = "Campo nome é obrigatorio")
    private String nome;

    @JsonInclude(Include.NON_NULL)
    @JsonFormat(pattern = "dd/mm/yyy")
    @NotNull(message = "Campo publicacao é obrigatorio")
    private Date publicacao;

    @JsonInclude(Include.NON_NULL)
    private String editora;

    @JsonInclude(Include.NON_NULL)
    private String resumo;

    @OneToMany( mappedBy = "livro", fetch = FetchType.LAZY )
    private List<Comentario> comentarios;

//Comentario.Java

@Entity
public class Comentario {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @JsonProperty("comentario")
    private String texto;

    private String usuario;

    @JsonFormat(pattern = "dd/mm/yyy")
    private Date data;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "LIVRO_ID")
    @JsonIgnore
    private Livro livro;

// Livrosrepository.java

package com.curso.repository;

import org.springframework.data.jpa.repository.JpaRepository;

import com.curso.domain.Livro;

public interface LivrosRepository extends JpaRepository<Livro, Long> {

}

//Comentariosrepository.java

package com.curso.repository;

import org.springframework.data.jpa.repository.JpaRepository;

import com.curso.domain.Comentario;

public interface ComentariosRepository extends JpaRepository<Comentario, Long> {



}

// Livrosservice.java

@Service
public class LivrosService {

    @Autowired
    private LivrosRepository livrosRepository;

    @Autowired
    private ComentariosRepository comentariosRepository;

   // [...]

    public List<Livro> listar() {
        return livrosRepository.findAll();
    }
}

When I make a Request to list the Books, the behavior I hope is that it lists all the book data, but without the comments, because I am using the annotation java fetch = FetchType.LAZY but the behavior I have is the return of all Book data.

[
    {
        "id": 4,
        "nome": "Teste2",
        "publicacao": "01/01/2018",
        "editora": "Polenta",
        "comentarios": [
            {
                "id": 1,
                "usuario": "tester",
                "data": "26/03/2019",
                "comentario": "Comentario 1"
            }
        ]
    }
]

Answer 1

Though you have declared one FetchType.LAZY in his JPA mapping, Jackson tends to get the object anyway because that’s his goal.

I don’t know your API, but in case you never want to expose the comments, you could just add a @JsonIgnore on your list.

Another technique would also be to have a specific DTO for your case to circumvent this situation.

Note: I looked a lot here about making Jackson understand this mapping in JPA, but unfortunately I couldn’t find anything viable. The most I could find was this post in which the author did everything to solve the problem, but could not.