Empty relation table

Question

I am doing some exercizes with JDBC/MariaDB trying to implement ER schema

Bigger image at address: http://img854.imageshack.us/img854/2513/psfl.jpg

So I started creating Java software

import java.sql.*;
import java.io.*;
import java.util.*;

import javax.sql.rowset.CachedRowSet;


class DBHandler_test
{  
    private Statement statement = null;
    private Connection connection = null;
    private ResultSet result = null;
    public DBHandler_test()
    {

    }

    public void createTables() throws SQLException, IOException, InstantiationException, IllegalAccessException, ClassNotFoundException
    {
        connection = getConnection();
        statement = connection.createStatement();
        statement.execute("DROP TABLE IF EXISTS Possiede");
        statement.execute("DROP TABLE IF EXISTS Possiede2");
        statement.execute("DROP TABLE IF EXISTS Possiede3");
        statement.execute("DROP TABLE IF EXISTS Camera");
        statement.execute("DROP TABLE IF EXISTS Oggetto");
        statement.execute("DROP TABLE IF EXISTS Parete");
        statement.execute("DROP TABLE IF EXISTS Accesso");



        statement.execute("CREATE TABLE IF NOT EXISTS Camera  (Nome CHAR(20) PRIMARY KEY, Estensione INT, `Livello_1` CHAR(20), `Livello_2` CHAR(20), `Livello_3` CHAR(20), `Livello_4` CHAR(20))");
        statement.execute("CREATE TABLE IF NOT EXISTS Accesso  (IdA INTEGER PRIMARY KEY, Coordinata__X INTEGER, Coordinata__Y INTEGER)");
        statement.execute("CREATE TABLE IF NOT EXISTS Oggetto (IdO INTEGER PRIMARY KEY, Nome CHAR(20), Coordinata_X INTEGER, Coordinata_Y INTEGER)");
        statement.execute("CREATE TABLE IF NOT EXISTS Parete (IdP INTEGER PRIMARY KEY, Coordinata_X CHAR(10), Coordinata_Y CHAR(10))");
        statement.execute("CREATE TABLE IF NOT EXISTS Possiede (IdO INTEGER NOT NULL, Nome CHAR(20), PRIMARY KEY (IdO), FOREIGN KEY (Nome) REFERENCES Camera(Nome), FOREIGN KEY (IdO) REFERENCES Oggetto(IdO))");
        statement.execute("CREATE TABLE IF NOT EXISTS Possiede2 (IdA INTEGER NOT NULL, Nome CHAR(20) NOT NULL, Coordinata_X INTEGER, Coordinata_Y INTEGER, PRIMARY KEY (IdA,Nome), FOREIGN KEY (IdA) REFERENCES Accesso(IdA), FOREIGN KEY (Nome) REFERENCES Camera(Nome))");
        statement.execute("CREATE TABLE IF NOT EXISTS Possiede3 (IdP INTEGER NOT NULL, Nome CHAR(20) NOT NULL,  PRIMARY KEY (IdP, Nome), FOREIGN KEY (Nome) REFERENCES Camera(Nome), FOREIGN KEY (IdP) REFERENCES Parete(IdP))");

        connection.close();
    }

    public void insertRoomsEntries() throws SQLException, IOException, InstantiationException, IllegalAccessException, ClassNotFoundException
    {
        connection = getConnection();
        statement = connection.createStatement();

        statement.execute("INSERT INTO Oggetto(IdO, Nome, Coordinata_X, Coordinata_Y) VALUES (1,'Cappelliera',3,2)");
        statement.execute("INSERT INTO Oggetto(IdO, Nome, Coordinata_X, Coordinata_Y) VALUES (2,'Attaccapanni',6,5)");
        statement.execute("INSERT INTO Oggetto(IdO, Nome, Coordinata_X, Coordinata_Y) VALUES (3,'Letto matrimoniale',3,10)");
        statement.execute("INSERT INTO Oggetto(IdO, Nome, Coordinata_X, Coordinata_Y) VALUES (4,'Comodino',3,9)");
        statement.execute("INSERT INTO Oggetto(IdO, Nome, Coordinata_X, Coordinata_Y) VALUES (5,'Comodino',3,12)");
        statement.execute("INSERT INTO Oggetto(IdO, Nome, Coordinata_X, Coordinata_Y) VALUES (6,'Armadio',7,3)");
        statement.execute("INSERT INTO Oggetto(IdO, Nome, Coordinata_X, Coordinata_Y) VALUES (7,'Bidet',8,2)");
        statement.execute("INSERT INTO Oggetto(IdO, Nome, Coordinata_X, Coordinata_Y) VALUES (8,'Water',10,2)");
        statement.execute("INSERT INTO Oggetto(IdO, Nome, Coordinata_X, Coordinata_Y) VALUES (9,'Lavandino',9,4)");
        statement.execute("INSERT INTO Oggetto(IdO, Nome, Coordinata_X, Coordinata_Y) VALUES (10,'Doccia',12,3)");
        statement.execute("INSERT INTO Oggetto(IdO, Nome, Coordinata_X, Coordinata_Y) VALUES (11,'Televisione',14,4)");
        statement.execute("INSERT INTO Oggetto(IdO, Nome, Coordinata_X, Coordinata_Y) VALUES (12,'Divano',17,5)");
        statement.execute("INSERT INTO Oggetto(IdO, Nome, Coordinata_X, Coordinata_Y) VALUES (13,'Tavolo',20,3)");
        statement.execute("INSERT INTO Oggetto(IdO, Nome, Coordinata_X, Coordinata_Y) VALUES (14,'Frigo',21,8)");
        statement.execute("INSERT INTO Oggetto(IdO, Nome, Coordinata_X, Coordinata_Y) VALUES (15,'Lavello',19,12)");
        statement.execute("INSERT INTO Oggetto(IdO, Nome, Coordinata_X, Coordinata_Y) VALUES (16,'Cestino',16,8)");
        statement.execute("INSERT INTO Oggetto(IdO, Nome, Coordinata_X, Coordinata_Y) VALUES (17,'Letto',8,9)");
        statement.execute("INSERT INTO Oggetto(IdO, Nome, Coordinata_X, Coordinata_Y) VALUES (18,'Comodino',7,8)");
        statement.execute("INSERT INTO Oggetto(IdO, Nome, Coordinata_X, Coordinata_Y) VALUES (19,'Cassettiera',11,8)");


        statement.execute("INSERT INTO Camera VALUES ('Ingresso', 28, 'Ingresso', 'NULL', 'NULL', 'NULL')");
        statement.execute("INSERT INTO Camera VALUES ('Camera da letto 1', 20, 'Ingresso', 'Camera da letto 1', 'NULL', 'NULL')");
        statement.execute("INSERT INTO Camera VALUES ('Bagno', 18, 'Ingresso', 'Corridoio 1', 'Bagno', 'NULL')");
        statement.execute("INSERT INTO Camera VALUES ('Corridoio 1', 20, 'Ingresso', 'Corridoio 1', 'NULL', 'NULL')");
        statement.execute("INSERT INTO Camera VALUES ('Salotto', 48, 'Ingresso', 'Corridoio 1', 'NULL', 'NULL')");
        statement.execute("INSERT INTO Camera VALUES ('Camera da letto 2', 15, 'Ingresso', 'Corridoio 2', 'Camera da letto 2', 'NULL')");
        statement.execute("INSERT INTO Camera VALUES ('Ripostiglio', 12, 'Ingresso', 'Corridoio 2', 'Ripostiglio', 'NULL')");
        statement.execute("INSERT INTO Camera VALUES ('Cucina', 30, 'Ingresso', 'Corridoio 1', 'Salotto', 'Cucina')");

        statement.execute("INSERT INTO Accesso VALUES (1, 6, 5)");
        statement.execute("INSERT INTO Accesso VALUES (2, 6, 7)");
        statement.execute("INSERT INTO Accesso VALUES (3, 11, 4)");
        statement.execute("INSERT INTO Accesso VALUES (4, 13, 5)");
        statement.execute("INSERT INTO Accesso VALUES (5, 18, 7)");
        statement.execute("INSERT INTO Accesso VALUES (6, 6, 12)");
        statement.execute("INSERT INTO Accesso VALUES (7, 10, 11)");
        statement.execute("INSERT INTO Accesso VALUES (8, 14, 12)");

        connection.close();
    }

    public static Connection getConnection()
       throws SQLException, IOException, InstantiationException, IllegalAccessException, ClassNotFoundException
    {  
       Properties props = new Properties();
       FileInputStream in = new FileInputStream("/home/caterpillar/workspace/BDC_esercitazione/src/database.properties");
       props.load(in);
       in.close();

       String drivers = props.getProperty("jdbc.drivers");
       if (drivers != null)
          System.setProperty("jdbc.drivers", drivers);
       String url = props.getProperty("jdbc.url");
       String username = props.getProperty("jdbc.username");
       String password = props.getProperty("jdbc.password");
       Class.forName(drivers).newInstance();
       return DriverManager.getConnection(url, username, password);
    }

    public static void main(String[] args)
    {
        DBHandler_test dbHandler = new DBHandler_test();
        try
        {
            dbHandler.createTables();
            dbHandler.insertRoomsEntries();
        }
        catch (SQLException e)
        {
            e.printStackTrace();
        }
        catch (IOException e)
        {
            e.printStackTrace();
        }
        catch (InstantiationException e)
        {
            e.printStackTrace();
        }
        catch (IllegalAccessException e)
        {
            e.printStackTrace();
        }
        catch (ClassNotFoundException e)
        {
            e.printStackTrace();
        }
    }
}

but when I open Possiede2 table in PHPmyadmin I see that is empty. How is it possible? Camera and Accesso tables are not empty. Did I made any mistakes in SQL commands?

Answer 1

I thought that referencing keys would have let Camera and Accesso to be present in Possiede2 but it seems to not be. So I have to manually enter entries, being carefull to choice entries that are in Camera and Accesso tables. One example of SQL code:

INSERT INTO Possiede2 VALUES (6, 'Ingresso', 6, 12)