How to implement a JPA birectional relation for entities that works from both sides-CodePudding

Another question regarding bi-directional relationship with JPA entities:

Suppose I have the following two classes:

@Entity
public class Product
{
    @Id
    private Long productID;

    @ManyToOne(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
    @JsonManagedReference
    @JoinColumn(name = "fk_supplier")
    private Supplier supplier;

    private String description;

    public Supplier getSupplier()
    {
        return supplier;
    }
}

And

@Entity
public class Supplier
{
    @Id
    private Long supplierID;

    @OneToMany(mappedBy = "supplier")
    @JsonBackReference
    private Set<Product> products = new HashSet<>();

    private String name;

    public Set<Product> getProducts()
    {
        return products;
    }
}

With those definitions, I get the results back that I want if I query for a product. For example like this:

{
    "productID": 1,
    "supplier": {
        "supplierID": 1,
        "name": "Acer"
    },
    "description": "Gaming chair"
}

But if I do it the other way round, thus querying a supplier, I only get this back:

{
    "supplierID": 1,
    "name": "Acer"
}

Here I am missing the products.

How can this be achieved?

CodePudding user response：

OneToMany is inherently lazy so if you want to load Supplier and all products you need to eagerly fetch the products

@OneToMany(fetch = FetchType.EAGER)

// or

@Query("select s from Supplier s left join fetch s.products  where s.supplierID = 1)

Also as you have a circular dependency between supplier and product you have used @JsonBackReference on the products collection which will prevent the products being serialised to json, hence your response

If you want to return Supplier with list of products or a product with the supplier and prevent circular dependency issues remove @JsonBackReference and @JsonManagedReference reference and use @JsonIgnoreProperties instead

    @JsonIgnoreProperties("products")
    @ManyToOne(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
    @JoinColumn(name = "fk_supplier")
    private Supplier supplier;

    @JsonIgnoreProperties("supplier")
    @OneToMany(mappedBy = "supplier", fetch = FetchType.EAGER)
    private Set<Product> products = new HashSet<>();