Question

What I was trying to do is that when I click the Add button it will create another instance where inside that instance there’s a QUERY that it will interact with the database, to add the input that I got from the JTextFields, and I have another problem it keeps on giving me an

m.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException

here is my action event code

private class AddHandler implements ActionListener {
        public void actionPerformed(ActionEvent event) {

                Personal personal = new Personal(firstTxt.getText(),miTxt.getText(),
                                    lastTxt.getText(),dob.getText(),maritalTxt.getText(),beneTxt.getText());
                Contact contact = new Contact(telTxt.getText(),addTxt.getText(),
                                    mobTxt.getText(),emailTxt.getText());
                Employee employee = new Employee(posTxt.getText(),payTTxt.getText(),payRTxt.getText(),hireTxt.getText());

                Finance finance = new Finance();

                finance.addEmployee(personal,contact,employee);


        }
    }

My addEmployee code

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();
        }


    }

here is the list of errors

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` FOREIGN KEY (`idpersonal_info`) REFERENCES `users` (`idusers`) ON DELETE CASCADE ON UPDATE CASCADE)

if you guys are wondering why I have foreign, is that I added a foreign key to it and it’s foreign key is idUsers, if you guys are wondering why I have a foreign key, I have a foreign key so that, if I Delete row, all of the other rows in the other tables will be deleted but it doesn’t work.

Answer 1

The following is the tables, I can assume from your question.

users          -- idusers, other fields
personal_info  -- idpersonal_info, First_Name, Middle_Initial, Last_Name, 
                  Date_Of_Birth, Marital_Status, Beneficiaries

And I assume the following relationship:

idusers         - primary key
idpersonal_info - foreign key referencing idusers, 
                  also, it is set to ON DELETE CASCADE, ON UPDATE CASCADE

                  You had set it as primary key with AUTO_INCREMENT also.

From Wikipedia on Foreign Key:

The values in one row of the referencing columns 
must occur in a single row in the referenced table.

If I understand your table structure correctly, then it put me to the following conclusion.

You are inserting a new record to personal_info table, but you omit the value for idpersonal_info since it is primary and auto_increment. Now, before insertion of the row, MySQL will perform a check on the foreign constraint you set. There, it checks to see, whether the value of idpersonal_info exists in idusers field of users table. Since you don’t specify a value for idpersonal_info, MySQL can take either NULL or an auto incremented value for idpersonal_info, which one will be taken by MySQL is I am not sure. If it takes NULL, then it will not be on users table, and hence the violation of foreign key constraint. If it takes an auto_incremented value, there is a chance that it will not present in the users table, and if not present, violates foreign key constraint.

Now, the solution which I can think of is that, you have to specify a value for idpersonal_info also in your INSERT query. You have to make sure that exists in the users table also.

Hope that helps 🙂