我是Web开发的新手。我一直在尝试建立一个电子商务平台,并使用@ManyToMany
作为联接表,在product
和wishlist
之间使用wishlist_product
映射。
添加后,我没有遇到错误,但是未将数据添加到联接表中。我已经尝试解决此问题已有2天了,但是一直面临着持续的失败。我已经在下面附上了wishlist
和product
的代码。
@Entity
@Table(name = "wishlist")
public class Wishlist {
@Id
@Column(name = "username")
/*
* @GeneratedValue(generator = "gen")
*
* @GenericGenerator(name = "gen", strategy = "foreign", parameters
* = @Parameter(name = "property", value = "login"))
*/
private String username;
@ManyToMany
@JoinTable(name = "wishlist_product",
joinColumns = @JoinColumn(name = "username"),
inverseJoinColumns = @JoinColumn(name = "product_id"))
private List<Electronics> product;
@Entity
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@Table(name = "electronics")
@DiscriminatorColumn(name = "product_Type", discriminatorType = DiscriminatorType.STRING)
public class Electronics {
@Id
@GenericGenerator(name = "CamIdGenerator", strategy = "com.virtusa.neuralhack.vlx.IdGenerator.CameraIdGenerator")
@GeneratedValue(generator = "CamIdGenerator")
// @GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "product_id")
private String productId;
private String askingPrice;
@Column(name = "age")
private String howOld;
@Column(name = "model")
private String model;
@Column(name = "brand")
private String brand;
@Column(name = "description")
private String description;
transient private String email;
@ManyToOne
@JoinColumn(name = "username")
private User_Login user;
@ManyToMany
@JoinTable(name = "wishlist_product", joinColumns = @JoinColumn(name = "product_id"), inverseJoinColumns = @JoinColumn(name = "username"))
private List<Wishlist> wishlist;
public void addToWishlist(String email, String productId) {
Session currentSession = manager.unwrap(Session.class);
Wishlist wishlist = currentSession.get(Wishlist.class,email);
//System.out.println(wishlist.getUser());
Electronics product = currentSession.get(Electronics.class, productId);
System.out.println(product);
wishlist.addToWishlist(product);
//product.addAWishlist(wishlist);
//System.out.println(wishlist.getProduct().get(0));
currentSession.saveOrUpdate(wishlist);
}
答案 0 :(得分:1)
您应该执行以下操作:
@Entity
@Table(name = "wishlist")
public class Wishlist {
@Id
@Column(name = "username")
private String username;
@ManyToMany(cascade = {CascadeType.PERSIST, CascadeType.MERGE})
@JoinTable(name = "wishlist_product",
joinColumns = @JoinColumn(name = "username"),
inverseJoinColumns = @JoinColumn(name = "product_id"))
private List<Electronics> products;
public void addProduct(Electronics product) {
products.add( product );
product.getWishlists().add( this );
}
public void removeProduct(Electronics product) {
products.remove( product );
product.getWishlists().remove( this );
}
}
@Entity
@Table(name = "electronics")
public class Electronics {
@Id
@Column(name = "product_id")
private String productId;
@ManyToMany(mappedBy = "products")
private List<Wishlist> wishlists;
}
仅@ManyToMany
注释应映射bidirectional @JoinTable
的拥有方。您应该在另一侧使用mappedBy
。
如果要传播持久状态和其他状态,则应在拥有方设置cascade
属性。
为保持双方之间的同步,优良作法是提供用于添加或删除子实体的辅助方法。
您的addToWishlist
方法将如下所示:
public void addToWishlist(String email, String productId) {
Session currentSession = manager.unwrap(Session.class);
Wishlist wishlist = currentSession.get(Wishlist.class,email);
Electronics product = currentSession.get(Electronics.class, productId);
wishlist.addProduct(product);
currentSession.saveOrUpdate(wishlist);
}
答案 1 :(得分:1)
确保您处于读写事务但不是只读事务。
一些建议:
cascade = CascadeType.ALL
与多对多关联使用,因为CascadeType.ALL
包括CascadeType.REMOVE
,如果多对多导致导致太多实体被删除