如何将主键的 ID 填充到外键

Question

I'm just new learning Java JDBC where I try to create a sample project.I created a two Prepared Statements which where I insert two queries for my tables. 1st table for Primary Key and 2nd table for Foreign Key. Using Statement_RETURN.GENERATED_KEYS is returning Id for Primary Key but in my Foreign Key its not populating and throwing me a value of null.

Parent Table

Child Table

QUERY:

    String insertALLSECTION_LIST = "INSERT INTO ALLSECTIONS_LIST (SECTION_NAME)"
            + "VALUES (?)";
    String insertALLSECTIONS_SETTINGS = "INSERT INTO ALLSECTIONS_SETTINGS (SECTION_POPULIMIT,ROOM_ASSGN,ADVISER_ASSIGNED,SESSION_ASSIGNED,YRLEVEL_ASSGN,SCHOOL_YEAR)"
            + "VALUES(?,?,?,?,?,?)";

Prepared Statements

    ResultSet generatedKeys = null;
    try (Connection myConn = DBUtil.connect())//Connection
    {
            myConn.setAutoCommit(false);//Turn off auto commit
            try (PreparedStatement myPs = myConn.prepareStatement(insertALLSECTION_LIST,Statement.RETURN_GENERATED_KEYS))//Prepared Statement
            {
                myPs.setString(1,inputSectionName);

                myPs.executeUpdate();

                myConn.commit();

                generatedKeys = myPs.getGeneratedKeys();
                if (generatedKeys.next())//Return ID
                {
                    sectionID = generatedKeys.getInt(1);
                }
                else
                {
                    throw new SQLException("No generated section ID returned");
                }

            }//end of try
            finally 
            {
                if (generatedKeys != null) generatedKeys.close();
            }//end of finally
            try (PreparedStatement myPs = myConn.prepareStatement(insertALLSECTIONS_SETTINGS))//Prepared Statement
            {
                myPs.setInt(1,inputStudentLimit);
                myPs.setString(2, inputRoomAssign);
                myPs.setString(3, inputAdviserAssign);
                myPs.setString(4, inputSession);
                myPs.setString(5, inputYearLevel);
                myPs.setString(6, inputSchoolYear);

                myPs.executeUpdate();

                myConn.commit();

                JOptionPane.showMessageDialog(null, "Insert Successful");
            }//end of try
    }//end of try       

1st Table (ALLSECTIONS_LIST)

As you can see here the Primary Key is populating.

2nd Table (ALLSECTIONS_SETTINGS)

Here where my SECTION_ID Column gives me null value.

But when I run my query for my tables. Still giving me a Null value for my Foreign Key. Feel free to comment. Thanks.

Answer 1

Once you get back the Auto Generated Key(s) as a result of your first Prepared Statement, you'll have to manually insert it into the other table.

Here are the modified queries:

String insertALLSECTION_LIST = "INSERT INTO ALLSECTIONS_LIST (SECTION_NAME)"
        + "VALUES (?)";

String insertALLSECTIONS_SETTINGS = "INSERT INTO ALLSECTIONS_SETTINGS (SECTION_ID,
        SECTION_POPULIMIT,ROOM_ASSGN,ADVISER_ASSIGNED,
        SESSION_ASSIGNED,YRLEVEL_ASSGN,SCHOOL_YEAR)"
        + "VALUES(?,?,?,?,?,?,?)";

Here is the code snippet:

ResultSet generatedKeys = null;
try (Connection myConn = DBUtil.connect()) {
    myConn.setAutoCommit(false);
    try (PreparedStatement myPs = myConn.prepareStatement(insertALLSECTION_LIST,
      Statement.RETURN_GENERATED_KEYS)) {
        myPs.setString(1,inputSectionName);
        myPs.executeUpdate();

        myConn.commit();
        generatedKeys = myPs.getGeneratedKeys();
        if (generatedKeys.next()) {
            sectionID = generatedKeys.getInt(1);
        } else {
            throw new SQLException("No generated section ID returned");
        }
    } finally {
        if (generatedKeys != null) generatedKeys.close();
    }

    try (PreparedStatement myPs = myConn.prepareStatement(insertALLSECTIONS_SETTINGS)) {
        /* Note : Change Here */
        myPs.setInt(1, sectionID);
        myPs.setInt(2, inputStudentLimit);
        myPs.setString(3, inputRoomAssign);
        myPs.setString(4, inputAdviserAssign);
        myPs.setString(5, inputSession);
        myPs.setString(6, inputYearLevel);
        myPs.setString(7, inputSchoolYear);
        myPs.executeUpdate();

        myConn.commit();
        JOptionPane.showMessageDialog(null, "Insert Successful");
    }
}