Relation N x N in Java objects

Question

I have an item table

(item_id (pk), descrição, ...),

A supplier table

(fornecedor_id (pk), nome, ...) 

and for being an Nxn relation I have an item_vendor intermediate table

(item_id (fk), fornecedor_id (fk), codigo, ...).

How do I create these 3 objects in Java (corresponding to each table), taking into account this relationship?

Answer 1

I’ll share a solution with you.

You will only need to get a few details such as field names to do the get and set and hashcode and equals methods of the 4 classes

Item class

@Entity
@Table(name = "item")
public class Item {

    @Id
    @Column(name = "item_id", length = 20, precision = 0)
    @GeneratedValue(strategy = GenerationType.AUTO) 
    private Long            id;

    @Column(name = "descricao")
    private String          descricao;

    //implementar os metodos corretamente hashCode equals, recomendavel

}

Supplier class

@Entity
@Table(name = "forncedor")
public class Fornecedor {

    @Id
    @Column(name = "forncedor_id", length = 20, precision = 0)
    @GeneratedValue(strategy = GenerationType.AUTO) 
    private Long            id;

    @Column(name = "nome")
    private String          nome;

    //implementar os metodos corretamente hashCode equals, recomendavel

}

Relation class, the relation fields must be equal and more Must be equal to the DDL of the table

@Table(name = "item_fornecedor")
@IdClass(ItemFornecedorPk.class)
public class ItemFornecedor {

    private ItemFornecedorPk    pk;

    @Id
    @ManyToOne
    @JoinColumn(name = "item_id_pk", referencedColumnName = "id")
    private Item        item;

    @Id
    @ManyToOne
    @JoinColumn(name = "forncedor_id_pk", referencedColumnName = "id")
    private Fornecedor          fornecedor;

    @Temporal(TemporalType.TIMESTAMP)
    @Column(name = "campoSoDaRelacao")
    private Date            campoSoDaRelacao;

    //implementar os metodos corretamente hashCode equals, obrigatório

}

Class of the relationship key

@Embeddable
public class ItemFornecedorPk {


    @Id
    @ManyToOne
    @JoinColumn(name = "forncedor_id_pk", referencedColumnName = "forncedor_id", insertable = false, updatable = false)
    private Fornecedor      fornecedor;

    @Id
    @ManyToOne
    @JoinColumn(name = "item_id_pk", referencedColumnName = "item_id", insertable = false, updatable = false)
    private Item        item;

    //implementar os metodos corretamente hashCode equals, obrigatório
}

Now it is put to the Factory or pesistyUnit read and it already works. da make the lists also in the father of each, but ai only if you need.