java05_main.java

Many-to-many. Three tables, two foreign key references constructing a many-to-many relationship. Populate with a few rows. Select and print from one side, then from the other.

import java.sql.*;
 
public class java05_main {
 
/*
                                                    
     * EXAMPLE - java05 for JDBC
                                                    
     * When you run this example, a new database is created with a two tables
                                                    
     * that need to be related via a many-to-many relationship, so an
                                                    
     * 'intersect' table is also created to keep track of that information.
                                                    
     * Three rows are inserted into each of the main tables and for each
                                                    
     * relationship a row is inserted into the intersect table.
                                                    
     * Finally all the data is read starting from one main table and printed
                                                    
     * and then the data is reread and printed starting from the other main
                                                    
     * table.
                                                    
     * 
                                                    
     * Full documentation for RDM is available at http://docs.raima.com/rdm/
                                                    
     * 
                                                    
     * For simplicity this example utilizes basic exception handling
                                                    
     * but good programming practices would dictate that this occur in 
                                                    
     * a full application.
                                                    
     */
                                                    
public static void main(String[] args) throws SQLException  {
 
        Connection conn = null;
        Statement stmt = null;
        ResultSet rs = null;

                                                    
try
                                                    
        {
/* Create the connection with a simple connection string */
                                                    
            conn = DriverManager.getConnection("jdbc:raima:rdm://local");
            conn.setAutoCommit(true);

                                                    
            CreateDatabase(conn);

                                                    
/* Open the connection to the database */
                                                    
            stmt = conn.createStatement();

                                                    
/* Insert three rows into the first main table */
                                                    
for (int ii = 1; ii < 4; ii++)
            {
                stmt.executeUpdate("INSERT INTO MainTab1 VALUES " + ii + ", 'main1 " + ii + "'");
            }
 
/* Insert three rows into the second main table */
                                                    
for (int ii = 1; ii < 4; ii++)
            {
                stmt.executeUpdate("INSERT INTO MainTab2 VALUES " + ii + ", 'main2 " + ii + "'");
            }
 
/* Insert a row into the intersect table for each combination of
                                                    
             * rows in the main tables */
                                                    
for (int ii = 1; ii < 4; ii++)
            {
for (int jj = 1; jj < 4; jj++)
                {
                        stmt.executeUpdate("INSERT INTO IntTab VALUES " + ii + ", " + jj);
                }
            }
 
/* Scan through the relationships from the first main table to the second */
                                                    
            System.out.println("From MainTab1 to MainTab2");
            rs = stmt.executeQuery("SELECT m1.str, m2.str FROM MainTab1 m1, MainTab2 m2, IntTab WHERE m1.id = IntTab.id1 AND m2.id = IntTab.id2");
while (rs.next() != false)
            {
                System.out.println(rs.getString(1) + " -- " + rs.getString(2));
            }
        }
catch (SQLException sqle)
        {
            sqle.printStackTrace();
        }
finally
                                                    
        {
if(rs != null)
                rs.close();
 
if(stmt != null)
                stmt.close();

                                                    
if(conn != null)
                conn.close();           
        }
    }

                                                    
private static void CreateDatabase(Connection conn)
    {
        Statement stmt = null;

                                                    
try
                                                    
        {
/* Create the example database */
                                                    
            stmt = conn.createStatement();
/* Since the database is created here, it cannot be created twice */
                                                    
try { 
                stmt.executeUpdate("DROP DATABASE java05");
            } catch (SQLException sqle) {} 
 
            stmt.execute("CREATE DATABASE java05");
            stmt.execute("CREATE TABLE MainTab1 (id INTEGER PRIMARY KEY, str CHAR(30))");
            stmt.execute("CREATE TABLE MainTab2 (id INTEGER PRIMARY KEY, str CHAR(30))");
            stmt.execute("CREATE TABLE IntTab (id1 INTEGER REFERENCES MainTab1(id), id2 INTEGER REFERENCES MainTab2(id))");
            conn.commit();
            stmt.close();
            stmt = null;
        }
catch (SQLException sqle)
        {
            sqle.printStackTrace();
        }
    }       
}