JPA中关联关系（OneToOne、OneToMany、ManyToMany，ManyToOne）映射代码片段

在使用Hibernate的时候我们常常会在类里边配置各种的关联关系，但是这个并不是很好配置，配置不当会出现各种各样的问题，下面具体来看一下：

package com.xz.springcloud.user;

import java.util.ArrayList;

import java.util.List;

import javax.persistence.CascadeType;

import javax.persistence.Entity;

import javax.persistence.FetchType;

import javax.persistence.GeneratedValue;

import javax.persistence.GenerationType;

import javax.persistence.Id;

import javax.persistence.JoinColumn;

import javax.persistence.JoinTable;

import javax.persistence.ManyToMany;

import javax.persistence.OneToOne;

import javax.persistence.Table;

import com.fasterxml.jackson.annotation.JsonManagedReference;

import lombok.Data;

import lombok.ToString;

@Data

//@ToString

@Entity

@Table(name="s_user")

public class User {

	@Id

	@GeneratedValue(strategy= GenerationType.AUTO)

	private Long id;

	private String username;

	private String password;

	private Integer age;

	private String gender;

	private String address;

	private String province;

	private String city;

	private String area;

	private Integer state;

	/**

	 * 注意看这里，双向一对第一

	 * 懒加载

	 */

	@OneToOne(fetch=FetchType.LAZY)

	@JoinColumn(name="identity_card")

	private IdentityCard identityCard;

	@JsonManagedReference

	@ManyToMany(cascade=CascadeType.ALL)

	@JoinTable(name="user_roles",joinColumns= {@JoinColumn(name="user_id")},inverseJoinColumns= {@JoinColumn(name="role_id")})

	private List<Role> roles = new ArrayList<>();

}

package com.xz.springcloud.user;

import java.io.Serializable;

import java.util.List;

import javax.persistence.Entity;

import javax.persistence.GeneratedValue;

import javax.persistence.GenerationType;

import javax.persistence.Id;

import javax.persistence.JoinColumn;

import javax.persistence.OneToOne;

import javax.persistence.Table;

import com.fasterxml.jackson.annotation.JsonBackReference;

import lombok.Data;

import lombok.ToString;

/**

 * 身份证类

 * @author yuxuan

 *

 */

@Data

//@ToString

@Entity

@Table(name="s_identity_card")

public class IdentityCard implements Serializable{

	@Id

	@GeneratedValue(strategy= GenerationType.AUTO)

	private Integer id;

	//身份证编号

	private String number;

	@JsonBackReference

	@OneToOne(mappedBy="identityCard")

	private User user;

}

看到这里可能有的人会问@JsonBackReference是个什么鬼，这个注解是为了阻断循环依赖，或者使用@JsonIgnore也行。在双向一对一或者一多的时候会产生循环依赖的问题，就是我中有你，你中有我。会一直无限循环下去，主要防止在SpringMVC中JSON解析返回的时候会出现溢出异常。

package com.xz.springcloud.user;

import java.util.ArrayList;

import java.util.List;

import javax.persistence.CascadeType;

import javax.persistence.Entity;

import javax.persistence.GeneratedValue;

import javax.persistence.GenerationType;

import javax.persistence.Id;

import javax.persistence.JoinColumn;

import javax.persistence.JoinTable;

import javax.persistence.ManyToMany;

import javax.persistence.Table;

import com.fasterxml.jackson.annotation.JsonBackReference;

import lombok.Data;

import lombok.ToString;

@Data

//@ToString

@Entity

@Table(name="s_role")

public class Role {

	@Id

	@GeneratedValue(strategy= GenerationType.AUTO)

	private Long id;

	private String roleName;

	private Integer userId;

	@JsonBackReference

	@ManyToMany(cascade=CascadeType.ALL)

	@JoinTable(name="user_roles",joinColumns= {@JoinColumn(name="role_id")},inverseJoinColumns= {@JoinColumn(name="user_id")})

	private List<User> users = new ArrayList<>();

}

有问题可以在下面评论，技术问题可以私聊我。