多表删除报错：
org.springframework.dao.DataIntegrityViolationException: could not execute statement; SQL [n/a]; constraint [null]; nested exception is org.hibernate.exception.ConstraintViolationException: could not execute statement
oujavaxeljavax.el-api2.2.4javax.el-api-2.2.4.jar;E:local_repository
epository_pinyougouorgglassfishwebjavax.el2.2.4javax.el-2.2.4.jar" com.intellij.rt.execution.junit.JUnitStarter -ideVersion5 -junit4 com.wsc.core.onetone.ManyToMany,deleteUser
log4j:WARN No appenders could be found for logger (org.springframework.test.context.junit4.SpringJUnit4ClassRunner).
log4j:WARN Please initialize the log4j system properly.
Hibernate: select user0_.user_id as user_id1_6_0_, user0_.password as password2_6_0_, user0_.username as username3_6_0_, role1_.userid as userid1_7_1_, role2_.role_id as roleid2_7_1_, role2_.role_id as role_id1_5_2_, role2_.memo as memo2_5_2_, role2_.role_name as role_nam3_5_2_ from user user0_ left outer join user_role role1_ on user0_.user_id=role1_.userid left outer join role role2_ on role1_.roleid=role2_.role_id where user0_.user_id=?
Hibernate: delete from user_role where userid=?
Hibernate: delete from role where role_id=?
Hibernate: delete from role where role_id=?
Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Cannot delete or update a parent row: a foreign key constraint fails (`shop`.`user_role`, CONSTRAINT `FKbo5ik0bthje7hum554xb17ry6` FOREIGN KEY (`roleid`) REFERENCES `role` (`role_id`))
分析：想要删除单个表数据报错
我的报错是在删除时：主要将中间表的外键约束删除，才能执行其他表的语句
用户表 角色表 中间表 三张表
顺序删除规则：先删除 中间表 （存在外键约束） 在执行主表 或 从表：存在外键约束，不能 执行SQL语句，
对策：
在从表 加上@ManyToMany(mappedBy = "role",fetch = FetchType.EAGER)
主表加上@ManyToMany(cascade = CascadeType.ALL,fetch = FetchType.EAGER)
执行结果：
1 com.wsc.core.onetone.ManyToMany,deleteUser 2 log4j:WARN No appenders could be found for logger (org.springframework.test.context.junit4.SpringJUnit4ClassRunner). 3 Hibernate: select user0_.user_id as user_id1_6_0_, user0_.password as password2_6_0_, user0_.username as username3_6_0_, role1_.userid as userid1_7_1_, role2_.role_id as roleid2_7_1_, role2_.role_id as role_id1_5_2_, role2_.memo as memo2_5_2_, role2_.role_name as role_nam3_5_2_ from user user0_ left outer join user_role role1_ on user0_.user_id=role1_.userid left outer join role role2_ on role1_.roleid=role2_.role_id where user0_.user_id=? 4 Hibernate: select user0_.roleid as roleid2_7_0_, user0_.userid as userid1_7_0_, user1_.user_id as user_id1_6_1_, user1_.password as password2_6_1_, user1_.username as username3_6_1_ from user_role user0_ inner join user user1_ on user0_.userid=user1_.user_id where user0_.roleid=? 5 Hibernate: select role0_.userid as userid1_7_0_, role0_.roleid as roleid2_7_0_, role1_.role_id as role_id1_5_1_, role1_.memo as memo2_5_1_, role1_.role_name as role_nam3_5_1_ from user_role role0_ inner join role role1_ on role0_.roleid=role1_.role_id where role0_.userid=? 6 Hibernate: select user0_.roleid as roleid2_7_0_, user0_.userid as userid1_7_0_, user1_.user_id as user_id1_6_1_, user1_.password as password2_6_1_, user1_.username as username3_6_1_ from user_role user0_ inner join user user1_ on user0_.userid=user1_.user_id where user0_.roleid=? 7 8 9 Hibernate: delete from user_role where userid=? 10 Hibernate: delete from user where user_id=? // 仅执行 两个删除语句，删除单表id OK！！！ 11 12 13 log4j:WARN Please initialize the log4j system properly. 14 15 Process finished with exit code 0
2....想要删除 两张表 ：必须删除所有你要删除的数据存在的外键约束，才能执行OK。
中间表 约束 id （两个表）
A(Id 主表) B (id 从表)
2 1
1 2
1 3
所以：要删除 id=2 ，必须删除 id=1 的 id=3 的也要删除。
执行方法：delete（1），delete（2），delete（3），就是全删除。