如何更新外键列？

Question

I have below tables:

create table TABLE1 ( id int(10) unsigned NOT NULL AUTO_INCREMENT, deptId int(11) NOT NULL, DeptName varchar(32) NOT NULL, PRIMARY KEY (id), KEY Dept (deptId, DeptName))

create table TABLE2 ( id int(10) unsigned NOT NULL AUTO_INCREMENT, empId int(11) NOT NULL, DeptName varchar(32) NOT NULL, PRIMARY KEY (id), KEY DeptName (DeptName), CONSTRAINT T2FK FOREIGN KEY (DeptName) REFERENCES TABLE1 (DeptName))

TABLE1 has a MUL key defined with both dept id and dept name. TABLE2 has a Foreign key which references only Dept name from TABLE1

The DTO for TABLE2 gets created like below:

@org.hibernate.annotations.NotFound(action = org.hibernate.annotations.NotFoundAction.IGNORE)
   @javax.persistence.ManyToOne(targetEntity = org.amru.persistence.dto.TABLE1DTOImpl.class, fetch=javax.persistence.FetchType.EAGER)
   @javax.persistence.JoinColumn(name = "deptName")
   public org.amru.persistence.dto.TABLE1DTO getTABLE1() {
      return TABLE1;
   } 

When I try to insert a row in TABLE2, it fails with foreign key constraint violation exception.

Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Cannot add or update a child row: a foreign key constraint fails (`amru`.`TABLE2`, CONSTRAINT `T2FK` FOREIGN KEY (`DeptName`) REFERENCES `TABLE1` (`DeptName`))

I also see a EntityExistsException when I debug

What is possibly wrong? Is it recommended to refer a part of MUL key as foreign key in another table?

I am using jpa, hibernate, jboss, ejb and mysql

Answer 1

Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: 
Cannot add or update a child row: a foreign key constraint fails

What is possibly wrong?

This is very clear that, DeptName is foreign key in TABLE2 , which is referring from TABLE1 . So, you are not allowed to change the value in parent table as the data is being referenced in other table.

If you are supposed to do this, then you need to alter your table to apply cascade changes to child table as well for your Foreign Key

FOREIGN KEY (DeptName) REFERENCES TABLE1 (DeptName) ON DELETE CASCADE ON UPDATE CASCADE