Spring data jpa: Entitie gets loaded multiple times

user_15268292 0
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So I have a relationship between an entity called Building and another entity called building unit. One building can have many building units. So a standard one to many relationships. The problem I'm facing is that every entity of the building unit is loaded 16 times instead of one as intended.

 public class Building {
    @OneToMany(mappedBy = "building",fetch = FetchType.EAGER, cascade = CascadeType.ALL)
    @JsonManagedReference //<- without this an endless recursion would appear
    private List<buildingUnit> buldingUnits;
    }

public class buildingUnit{
    @ManyToOne()
    @JoinColumn(name = "building_id, nullable = false)
    @JsonBackReference
    private Building building
}

The building also has a relationship with different classes and the building unit has also some more relationships with different classes but I don't think that they will produce this behaviour. I shut mention that in the database everything is stored correctly. Every Building unit is stored once and has a forging-key to a building. So the issue has to come from the code.

The relations of my entities are somewhat like this:

            BuildingUnit    ->
Building ->                    Room -> Wall 
            VentilationZone ->

building unit and ventilation zone can have different rooms

The Result when I load a building from the DB:

Building:
 buildingUnit: [u1, u1, u1, u1, u1,..., u2, u2, u2, u2,...]

The DB I'm using is an SQLite DB

spring-data-jpa spring java
3 Answers

I'm not sure if you posted the entire code but I think you are missing the @Entity and @Id. Like the following example:

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

...

If it does not fix the problem, it may be worth implementing the equals and hashcode methods.

user_10907450

Maybe because of other collection in your building entity that's getting fetched eagerly ,which will cause a cartesian product due to the double left outer join.

user_126663010

Work around:

I couldn't find a solution to the problem but I found a workaround which removes all duplicates. In the Repository where the buildings are loaded I run a short function which remove all duplicated objects:

private void removeDubplicates(Building building){
    building.setBuildingUnits(
        building.getBuildingUnits.stream()
                                 .distinct()
                                 .collect(Collectors.ToList())                        
    );
}

I think this works because every duplicate in the list is the same object(o1 == o2).

user_152682920
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