Question

I was working with UIs where the user will click the add button to add employees, but when I do it, it gives me an error like this

com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Cannot add or update a child row: a foreign key constraint fails (`finalpayroll`.`personal_info`, CONSTRAINT `personal_info_ibfk_1` 

How would I fix this?? I know I am using a parent key, and its foreign key is the User, and also take note that the parent key has already a data, but it seems my query won’t work, why is that? I am using a foreign key with delete cascade and on update cascade so that when I delete a data, all of the child table rows will be deleted, vice versa. here’s my key for adding or inserting statements

public void addEmployee(Personal p ,Contact c,Employee e) {
    Connection conn = Jdbc.dbConn();
    Statement statement = null;
    String insert1 = "INSERT INTO personal_info (`First_Name`, `Middle_Initial`, `Last_Name`, `Date_Of_Birth`, `Marital_Status`, `Beneficiaries`) VALUES ('"+p.getFirstName()+"', '"+p.getMiddleInitial()+"'" +
                "       , '"+p.getLastName()+"', '"+p.getDateOfBirth()+"', '"+p.getMaritalStatus()+"', '"+p.getBeneficiaries()+"')";
    try {
        statement = conn.createStatement();
        statement.executeUpdate(insert1);
        statement.close();
        conn.close();
        JOptionPane.showMessageDialog(null, "Employee Added!!");
    } catch(Exception ex) {
        ex.printStackTrace();
    }
}

Users table:

CREATE TABLE `users` (
  `idusers` int(11) NOT NULL AUTO_INCREMENT,
  `emp_id` varchar(45) DEFAULT NULL,
  `emp_pass` varchar(45) DEFAULT NULL,
  PRIMARY KEY (`idusers`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=latin1

Personal_info table:

CREATE TABLE `personal_info` (
    `idpersonal_info` int(11) NOT NULL AUTO_INCREMENT,
    `First_Name` varchar(45) DEFAULT NULL,
    `Middle_Initial` varchar(45) DEFAULT NULL,
    `Last_Name` varchar(45) DEFAULT NULL,
    `Date_Of_Birth` varchar(45) DEFAULT NULL,
    `Marital_Status` varchar(45) DEFAULT NULL,
    `Beneficiaries` varchar(45) DEFAULT NULL,
    PRIMARY KEY (`idpersonal_info`),
    CONSTRAINT `personal_info_ibfk_1`
    FOREIGN KEY (`idpersonal_info`)
    REFERENCES `users` (`idusers`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=latin1

Answer 1

You are trying to insert a record with 6 fields: First_Name, Middle_Initial, Last_Name, Date_Of_Birth, Marital_Status and Beneficiaries. Your schema is currently unknown but none of these fields seem to be a candidate foreign key to id of User table you mentioned. Thus I think there is a default value for that foreign key column and that default value is missing in User table.

Needless to say, you shouldn’t have a default value for a foreign key of any table..

I am adding these information regarding your questions in comments and update on your question:

A foreign key is a link between a child table and parent table, personal_info and users tables in your case respectively. Child table’s foreign key column must reference to a key value in parent table which means that for every value in child table’s FK column, there must be a value in parent table’s linked column.

Now, in your case when you try to insert a new personal_info record MySQL assigns a idpersonal_info to it, since you defined it as auto increment. But since there is a link to users table, MySQL searchs for the new idpersonal_info to be inserted in users table’s idusers column. And as you are getting this exception, you surely don’t have that value in the users table.

You can change your table structure as follows:

CREATE TABLE `personal_info` (
  `idpersonal_info` int(11) NOT NULL AUTO_INCREMENT,
  `user_id` int(11) NOT NULL,

  ... OTHER FIELD DEFINITIONS,

  PRIMARY KEY (`idpersonal_info`),
  CONSTRAINT `user_id_fk_1` FOREIGN KEY (`user_id`) REFERENCES `users` (`idusers`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB

And your query will need to include user_id field as well. So it will be something like this:

INSERT INTO personal_info
  (`user_id`, `First_Name`, `Middle_Initial`, `Last_Name`, `Date_Of_Birth`, `Marital_Status`, `Beneficiaries`)
VALUES ( .... SET YOUR VALUES HERE. DON'T FORGET TO SET A VALID USER_ID