2、错误原因。

  在多对多保存测试的过程中，常常会出现以上错误信息，出现错误信息的原因是id值没有传进去，需要手动赋值。

如User和Role两个类是多对多关系，Role是维护端，User是维护端，具体代码：

package sys.entity;

import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;

import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
import javax.persistence.Table;
@Table(name="a_role")
@Entity
public class Role implements Serializable{
	private Integer id;
	private String roleName;
	private Set<User>users=new HashSet<User>();
	@GeneratedValue
	@Id
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id==null?null:id;
	}
	public String getRoleName() {
		return roleName;
	}
	public void setRoleName(String roleName) {
		this.roleName = roleName;
	}
	
	@ManyToMany(mappedBy="roles")
	public Set<User> getUsers() {
		return users;
	}
	public void setUsers(Set<User> users) {
		this.users = users;
	}
	
}

package sys.entity;
import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;

import javax.persistence.CascadeType;
import javax.persistence.Column;
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.Table;

import sys.util.Constant;
@Table(name="a_user")
@Entity
public class User implements Serializable{
	private Integer id;
	
	private String username;//用户名
	private String password;//密码
	
	private Set<Role>roles=new HashSet<Role>();
	@GeneratedValue(strategy=GenerationType.IDENTITY)
	@Id
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id==null?null:id;
	}
	public String getUsername() {
		return username;
	}
	public void setUsername(String username) {
		this.username = username;
	}
	
	@Column(length=64)
	public String getPassword() {
		return password;
	}
	public void setPassword(String password) {
		this.password = password;
	}

	@JoinTable(name="a_user_role",joinColumns={@JoinColumn(name="userId",referencedColumnName="id")},
			inverseJoinColumns={@JoinColumn(name="roleId",referencedColumnName="id")})
	@ManyToMany(cascade={CascadeType.PERSIST,CascadeType.MERGE},fetch=FetchType.EAGER)
	public Set<Role> getRoles() {
		return roles;
	}
	public void setRoles(Set<Role> roles) {
		this.roles = roles;
	}
	
	
	
	

}

3、测试：

@Test
	public void test6() {
		// 1、级联保存
		Set<Role>roles=new HashSet<Role>();
		Set<User>users=new HashSet<User>();
		Role role=roleService.getRole(1);
		role.setUsers(users);
		roles.add(role);
		User user=new User();
		//user.setId(-1);
		user.setUsername("李彤");
		user.setPassword("1144");
		user.setRoles(roles);
		users.add(user);
		userService.save(user);
	}
	

一测试就会出现以上错误！

4、解决方法。　

解决的方法是设置一个Id值，任意设，如

user.setId(-1);

org.springframework.dao.InvalidDataAccessApiUsageException: detached entity passed to persist: sys.entity.Role; nested exception is org.hibernate.PersistentObjectException: 的解决方案

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