JPA双向多对多关联关系@ManyToMany
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2022-04-23 16:54:20
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package com.jpa.helloworld;
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.ManyToMany;
import javax.persistence.Table;
@Table(name="CATEGORYS")
@Entity
public class Category {
private Integer cID;
private String cName;
private Set<Item> items = new HashSet<Item>();
@Id
@Column(name="C_ID")
@GeneratedValue
public Integer getcID() {
return cID;
}
public void setcID(Integer cID) {
this.cID = cID;
}
@Column(name="C_NAME")
public String getcName() {
return cName;
}
public void setcName(String cName) {
this.cName = cName;
}
//添加了mappedBy属性则不能使用@JoinTable注解
@ManyToMany(mappedBy="categorys")
public Set<Item> getItems() {
return items;
}
public void setItems(Set<Item> items) {
this.items = items;
}
}
package com.jpa.helloworld;
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="ITEMS")
@Entity
public class Item {
private Integer iId;
private String iName;
private Set<Category> categorys = new HashSet<Category>();
@Id
@GeneratedValue
@Column(name="I_ID")
public Integer getiId() {
return iId;
}
public void setiId(Integer iId) {
this.iId = iId;
}
@Column(name="I_NAME")
public String getiName() {
return iName;
}
public void setiName(String iName) {
this.iName = iName;
}
//使用@JoinTable注解添加中间表
//其中name属性设置中间表的表名
//joinCloums属性在中间表中添加的列
//JoinColumns属性:
// @joinColumn属性设置中间表中的列名
// referencedColumnName属性指向被映射表的主键(可以没有该属性)
//@inverseJoinColumns另外一张表在中间表中的列
@JoinTable(
name="ITEMS_CATEGORYS",
// joinColumns = {@JoinColumn(name="ITEM_ID",referencedColumnName="I_ID")},
joinColumns = {@JoinColumn(name="ITEM_ID")},
// inverseJoinColumns= {@JoinColumn(name="CATEGORY_ID", referencedColumnName="C_ID")})
inverseJoinColumns= {@JoinColumn(name="CATEGORY_ID")})
@ManyToMany
public Set<Category> getCategorys() {
return categorys;
}
public void setCategorys(Set<Category> categorys) {
this.categorys = categorys;
}
}