how to suppress loading related nested entity

Question

I have the following entities in my spring boot app, which is serving an API for a front end:

@Entity
public class Company {
    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "seq_company")
    @SequenceGenerator(name = "seq_company", allocationSize = 1)
    @Column(nullable = false, updatable = false)
    private Long id;
    private String name;
    private String shortName;
}

@Entity
public class Plant {
    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "seq_plant")
    @SequenceGenerator(name = "seq_plant", allocationSize = 1)
    @Column(nullable = false, updatable = false)
    private Long id;
    private String code;
    private String location;
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name="companyid", nullable = false)
    private Company company;
}

@Entity
public class PlantArea {
    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "seq_plantarea")
    @SequenceGenerator(name = "seq_plantarea", allocationSize = 1)
    @Column(nullable = false, updatable = false)
    private Long id;
    private String code;
    private String name;
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name="plantid", nullable = false)
    private Plant plant;
}

Each company can have one or more plants and each plant can have one or more plantareas. Notice, that I don't have any List properties in the entities, this is not needed.

For querying the entities I use @EntityGraph in order to avoid the famous n+1 select problem.

This is how I get all plants in the repository interface:

@EntityGraph(type = EntityGraph.EntityGraphType.FETCH, attributePaths = {"company"})
List<Plant> findAll();

Since the API needs the related company entity, I fetch it. With this I get what I want, it's all fine.

Now, this is how I get all plant areas:

@EntityGraph(type = EntityGraph.EntityGraphType.FETCH, attributePaths = {"plant", "plant.company"})
List<PlantArea> findAll();

Notice the plant.company attribute path. With this I get obviously the full chain of entities: plantarea -> plant -> company. This works too.

But for the front end if I query for all plant areas, I don't need the related company entities, just the plant entities. But if I remove the plant.company attribute path, I get the following error pointing to the company property in the plant entity:

No serializer found for class org.hibernate.proxy.pojo.bytebuddy.ByteBuddyInterceptor and no properties discovered to create BeanSerializer

I googled this and can resolve this, if I put this line of code (annotate the company property) in the plant entity:

@JsonIgnoreProperties({"hibernateLazyInitializer", "handler"})

But in this case I get the n+1 select problem and on top I get the related company entities too (which I don't want).

So, the question is: how can I select all plantarea entities with the related plant entity, but without the related company entity? And all that without using the above @JsonIgnoreProperties annotation.

You’re looking to do partial JSON serialisation - you need a view. https://www.baeldung.com/jackson-json-view-annotation — Boris the Spider, Jan 18 '22 at 19:34
if you consider to take my advice (2) that i already told you in [this](https://stackoverflow.com/a/70731411/339637) , you do not need do worry about such issue. I also just told another user the same advice in [this](https://stackoverflow.com/a/70761431/339637) — Ken Chan, Jan 18 '22 at 20:02
You are certainly right and I will give it a try today evening. — derstauner, Jan 19 '22 at 06:41

score 0 · Answer 1 · answered Jan 20 '22 at 19:24

After studying the DTO pattern, I created this dto:

public class PlantAreaDto {
    @JsonProperty("id")
    private Long id;
    @JsonProperty("code")
    private String code;
    @JsonProperty("name")
    private String name;
    @JsonProperty("plant")
    private Plant plant;
    @JsonProperty("company")
    private Company company;
}

Note, that the company property is no more part of the entity, I removed it and populate it in the mapper like this:

@Mapper(componentModel = "spring")
public interface PlantAreaMapper extends BaseMapper<PlantAreaDto, PlantArea> {
    @Override
    @Mapping(target = "company", source = "plant.company")
    PlantAreaDto toDto(PlantArea plantArea);
}

And the repository looks like this:

@Repository
public interface PlantAreaRepository extends JpaRepository<PlantArea, Long> {
    @EntityGraph(type = EntityGraph.EntityGraphType.FETCH, attributePaths = {"plant", "plant.company"})
    List<PlantArea> findAll();
}

With this I got, what I wanted:

no need to persist the company entity in the db, instead it will be populated from the plant property
the company property of the plant entity is now fetched from db, but I don't have the n+1 select problem and I don't get the No serializer found... error
I get all the data with one query

how to suppress loading related nested entity

1 Answers1