jpa 多对多

entity   Item

package entity;

import java.util.HashSet;
import java.util.Set;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.Table;

@Table(name = "tb_items")
@Entity
public class Item {
    private Integer id;
    private String itemName;
    /**
     * 多对多的关系
     */
    private Set<Category> categories = new HashSet<>();

    @GeneratedValue
    @Id
    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    @Column(name = "ITEM_NAME")
    public String getItemName() {
        return itemName;
    }

    public void setItemName(String itemName) {
        this.itemName = itemName;
    }

    // joinColumns：指定自己的外键和中间表之关联的之列
    // @JoinColumn(name="ITEM_ID" 中间表的外键
    // referencedColumnName="ID"  自己的主键
    // ****inverseJoinColumns：指定与之相关表的外键和与之关联的之列
    //name="ITEM_CATEGORY":指定中间表的表名
    @JoinTable(name="ITEM_CATEGORY",
       joinColumns = { @JoinColumn(name = "ITEM_ID", referencedColumnName = "ID") },
       inverseJoinColumns = {@JoinColumn(name = "CATEGORY_ID", referencedColumnName = "ID") })
    @ManyToMany
    public Set<Category> getCategories() {
        return categories;
    }

    public void setCategories(Set<Category> categories) {
        this.categories = categories;
    }

    @Override
    public String toString() {
        return "Item [>;
    }

}

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