在EclipseLink提供的JPA中向多对多关系中添加行/从多对多关系中删除行

Question

复制和粘贴我前面问题的一些介绍部分。

我在Eclipselink2.3.2中使用JPA2.0，在其中，我在产品和它们的颜色之间建立了多对多的关系。一个产品可以有多种颜色，一种颜色可以与多种产品相关联。这种关系在数据库中由三个表表示。

null

public void addToProduct(Product product) {
    this.getProductSet().add(product);
    product.getColourSet().add(this);
}

public void removeFromProduct(Product product) {
    this.getProductSet().remove(product);
    product.getColourSet().remove(this);
}

@Override
@SuppressWarnings("unchecked")
public void insert(List<Colour> colours, Product product) {
    for (Colour colour : colours) {
        colour.addToProduct(product);
    }
}

@Override
@SuppressWarnings("unchecked")
public void delete(Colour colour, Product product) {
    colour.removeFromProduct(product);
}

public class Product implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Basic(optional = false)
    @Column(name = "prod_id")
    private Long prodId;

    private static final long serialVersionUID = 1L;

    @JoinTable(name = "prod_colour", joinColumns = {
        @JoinColumn(name = "prod_id",
                    referencedColumnName = "prod_id")},
                    inverseJoinColumns = {
                        @JoinColumn(name = "colour_id", referencedColumnName = "colour_id")})
    @ManyToMany(fetch = FetchType.LAZY)
    private Set<Colour> colourSet;

    //Getters and Setters.
}

colour实体类。

public class Colour implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Basic(optional = false)
    @Column(name = "colour_id")
    private Long colourId;

    private static final long serialVersionUID = 1L;

    @ManyToMany(mappedBy = "colourSet", fetch = FetchType.LAZY)

    private Set<Product> productSet;

    //Setters and getters.
}

Answer 1

为了更新该连接表，您需要例如完全/急切加载的实体，并且在编写代码之后，不要忘记调用：

entityManager.merge(colour);
entityManager.merge(product);