Migration from MySql to Derby

Question

I am currently migrating from MySql to Derby.
I have been developing a MRPII package for a while now and whilst my classes worked with MySql I am finding difficulty with implementing them using Derby.
I have developed a GUI interface for MRPII functions and use a Database Interface class to connect to the database.
The Database Interface class gives me the capability of reading and writing from a database.
I extend this capability to sub classes ie part, customers, suppliers, work orders.
The problem I have is with the ' "+standardCost+" ' type statements. In MySql, the database engine recognises that the standard cost variable is a double though using Derby I get the following Errors.
SQL Exception: Columns of type 'DOUBLE' cannot hold values of type 'CHAR'. In Save Data error code30000
SQL Exception: Columns of type 'DOUBLE' cannot hold values of type 'CHAR'. In Save Data error code30000
Executed statement INSERT INTO stock VALUES('BUDGET500','A1', '100.0','50.0','1.0','100.0')
Executed statement INSERT INTO part VALUES('BUDGET500', 'PENTIUM','76.0', '86.0','EACH','MP','7','33')
The only solution I see is giving each subclass of Database Interface the individual capability within that class to connect to the database and use prepared statements.
Does anyone know if Derby has the capability of processing the updates using a similar format as shown in my code.
package delta.databaseInterface;
import delta.databaseInterface.DatabaseInterface;
public class Part extends DatabaseInterface{
     private String partNumber;
     private String partType;
     private String description;
     private double standardCost;
     private double sellingPrice;
     private String stockLocation;
     private double quantityOnHand;
     private String unitOfMeasure;
     private double minimumStock;
     private double minimumOrderQuantity;
     private int leadTime;
     private double avaliableStock;
                     private int commodityCode;
     public void setPartNumber(String pn){
          this.partNumber = pn.toUpperCase();
     public void setDescription(String ds){
          this.description = ds.toUpperCase();
     public void setStandardCost(double sc){
          this.standardCost = sc;
     public void setSellingPrice(double sp){
          this.sellingPrice = sp;
     public void setQuantityOnHand(double qt){
          this.quantityOnHand = qt;
          this.avaliableStock = qt;
     public void setStockLocation(String sl){
          this.stockLocation = sl.toUpperCase();
     public void setUnitOfMeasure(String uom){
          this.unitOfMeasure = uom.toUpperCase();
     public void setTypeOfPart(String top){
          this.partType = top.toUpperCase();
     public void setMinimumStock(double ms){
          this.minimumStock= ms;
     public void setMinimumOrderQuantity(double moq){
          this.minimumOrderQuantity = moq;
     public void setLeadTime(int lt){
          this.leadTime = lt;
                     public void setCommodityCode(int cc){
          this.commodityCode = cc;
     public void insertIntoPartDatabase(){
       super.setDatabase("mrpii");
                       super.setUpdate( "INSERT INTO part VALUES('"+partNumber+"', '"+description+"','"+standardCost+"'," +
       " '"+sellingPrice+"','"+unitOfMeasure+"','"+partType+"','"+leadTime+"','"+commodityCode+"')");
                         super.saveData();       
     public void insertIntoStockDatabase(){
        super.setDatabase("mrpii");
        super.setUpdate("INSERT INTO stock VALUES('"+partNumber+"','"+stockLocation+"',"+
" '"+quantityOnHand+"','"+minimumStock+"','"+minimumOrderQuantity+"','"+avaliableStock+"')");
                super.saveData();
     public void changePartDetails(){
        super.setDatabase("mrpii");
        super.setUpdate( "UPDATE part SET description = '"+description+"',unitOfMeasure = '"+unitOfMeasure+"',"+
          "partType = '"+partType+"' WHERE partNumber = '"+partNumber+"' ");
        super.saveData();
     public void adjustStock(){
          super.setDatabase("mrpii");
          super.setUpdate( "UPDATE stock SET stockLocation = '"+stockLocation+"',"+
          "avaliableStock = (('"+quantityOnHand+"' - qtyOnHand ) + avaliableStock), "+
          " qtyOnHand = '"+quantityOnHand+"' WHERE partNumber = '"+partNumber+"' ");
          super.saveData();
     public void insertAllocation(String allocationID, double quantity){
          super.setDatabase("mrpii");
          super.setQuery("INSERT INTO allocations VALUES('"+partNumber+"','"+quantity+"',"+
             " '"+allocationID+"')");
          super.saveData();
     public void reduceAvaliable(double allocated){
          super.setDatabase("mrpii");
          super.setUpdate( "UPDATE stock SET avaliableStock = (avaliableStock - '"+allocated+"') WHERE " +
          "partNumber = '"+partNumber+"' ");
          super.saveData();
     public void increaseAvaliable(double allocated){
          super.setDatabase("mrpii");
          super.setUpdate( "UPDATE stock SET avaliableStock = (avaliableStock - '"+allocated+"') WHERE " +
          "partNumber = '"+partNumber+"' ");
          super.saveData();
}Any help would be deeply appreciated
Thanks
Jim

Answer 1

I am currently migrating from MySql to Derby. Dear God, why?I am using the embedded functionality.
>
I have been developing a MRPII package for a whilenow
MRP as in "manufacturing resource planning"?Yes
>
and whilst my classes worked with MySql I am
finding difficulty with implementing them using
Derby.That suggests that your Java code relies too heavily
on MySQL features. You didn't make your code
portable enough.
I have developed a GUI interface for MRPIIfunctions
and use a Database Interface class to connect tothe
database.
The Database Interface class gives me thecapability
of reading and writing from a database.
I extend this capability to sub classes ie part,
customers, suppliers, work orders.
The problem I have is with the ' "+standardCost+"'
type statements. In MySql, the database engine
recognises that the standard cost variable is a
double though using Derby I get the following
Errors.Right - you're counting on something that might not
be true for all databases. MySQL appears to be doing
an implicit conversion from string to double. Bad
idea.
SQL Exception: Columns of type 'DOUBLE' cannothold
values of type 'CHAR'. In Save Data errorcode30000
SQL Exception: Columns of type 'DOUBLE' cannothold
values of type 'CHAR'. In Save Data errorcode30000
Executed statement INSERT INTO stock
VALUES('BUDGET500','A1',
'100.0','50.0','1.0','100.0')
Executed statement INSERT INTO part
VALUES('BUDGET500', 'PENTIUM','76.0',
'86.0','EACH','MP','7','33')Do you use PreparedStatements to escape strings and
dates for you? If not, you're in for a bumpy ride.
The only solution I see is giving each subclass of
Database Interface the individual capabilitywithin
that class to connect to the database and use
prepared statements.I would not have a single database interface. Each
class has its own requirements. How can a single
class know about all of them? Better to break your
persistence layer into several interaces, one per
persistent class.That is what I thought
>
Does anyone know if Derby has the capability of
processing the updates using a similar format as
shown in my code.I think your code is in trouble, Jim.Probably so, thought a redesign is not so much of a problem now as I am a bit more experienced than when I started out.
>
You don't use prepared statements, which would help
with your portability issues.
You have SQL embedded in the objects. I'd move it
out into a separate persistence layer.
You might want to read about Hibernate, an
object/relational mapping layer. You've got objects
and tables. Hibernate tools or Middlegen can
generate the XML mapping files for you. Once you
have those, you'll find that Hibernate will make
porting to another database a lot easier. It can be
as easy as changing configuration files.
I'd also look into Spring. It has some great
plumbing to help you deal with databases and lots of
other stuff.
%My main class is as follows;
package delta.databaseInterface;
* @author James Charles
import java.sql.SQLException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.Statement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.util.Vector;
import javax.swing.JTable;
public class DatabaseInterface{
     private String database;
     private String query;
                     private String update;
            private String[][] results = new String[0][0];
     private int columnCount = 0;
     private int rowCount = 0;
     private boolean resultsExist = false;
     Object data[][];
     private JTable table;
     public void setDatabase(String database){
          this.database = database;
     public void setQuery(String query){
          this.query = query;
            public void setUpdate(String update){
          this.update= update;
        public void saveData(){
          try{
          Class.forName("org.apache.derby.jdbc.EmbeddedDriver").newInstance();
          String sourceURL = new String("jdbc:derby:" + this.database);
          Connection databaseConnection = DriverManager.getConnection(sourceURL);
          Statement statement = databaseConnection.createStatement();
          statement. executeUpdate(this.update);
                databaseConnection.close();
          } // end of try
          catch(ClassNotFoundException cnfe){
               System.err.println(cnfe);
          catch(SQLException sqle){
               System.err.println(sqle + " In Save Data error code" + sqle.getErrorCode());
                         System.out.println("Executed statement " + this.query);
                catch(InstantiationException ie){
                    System.err.println(ie);
         catch(IllegalAccessException iae){
                    System.err.println(iae);
     public String getDatabase(){
          return this.database;
     public String getQuery(){
          return this.query;
     public void setResults(){           
     try{
          Class.forName("org.apache.derby.jdbc.EmbeddedDriver").newInstance();
          String sourceURL = new String("jdbc:derby:" + this.database);
          Connection databaseConnection = DriverManager.getConnection(sourceURL);
          Statement statement = databaseConnection.createStatement();
          ResultSet thisResult = statement.executeQuery(this.query);
                databaseConnection.commit();
          System.out.println("Executed statement");
          convertToArray(thisResult);
          databaseConnection.close();
     } // end of try
     catch(ClassNotFoundException cnfe){
          System.err.println(cnfe);
     catch(SQLException sqle){
          System.err.println(sqle);
     catch(InstantiationException ie){
                    System.err.println(ie);
         catch(IllegalAccessException iae){
                    System.err.println(iae);
     public void convertToArray(ResultSet resultsIn) throws SQLException{
          this.resultsExist = false;
          String[] columnNames = new String[0];
          Vector dataRows = new Vector();
          ResultSetMetaData metadata = resultsIn.getMetaData();
          this.columnCount = metadata.getColumnCount();
          columnNames = new String[this.columnCount];
          for(int i = 0; i < this.columnCount; i++)
               columnNames[i] = metadata.getColumnLabel(i+1);
          String[] rowData = new String[this.columnCount]; // Stores one row
          while(resultsIn.next()){ // For each row...
               rowData = new String[this.columnCount]; // create array to hold thedata
                    for(int i = 0; i < this.columnCount; i++)// For each column
                    rowData[i] = resultsIn.getString(i+1); // retrieve the data item
                    dataRows.addElement(rowData); // Store the row in the vector
          this.results= new String[dataRows.size()][this.columnCount];
          this.data= new Object[dataRows.size()][this.columnCount];
          for(int column = 0; column < this.columnCount; column++)
               for(int row = 0; row < dataRows.size(); row++){
          this.results[row][column] = ((String[])(dataRows.elementAt(row)))[column];
          this.data[row][column] = ((String[])(dataRows.elementAt(row)))[column];
          this.rowCount = dataRows.size();
          try{
               if  (results[0][0].equals(null)){ this.resultsExist = false;} //ckecks results
                    else {this.resultsExist = true;}
               catch (ArrayIndexOutOfBoundsException e){
               System.out.println(e + "in catch");
               this.resultsExist = false;
               System.out.println("Value of exists in catch = " + this.resultsExist);
     }// end of set results
     public JTable getTable(Object[] columnNames) {
          table = new JTable(data, columnNames);
          return table;
     public int getColumnCount(){
          return this.columnCount;
     public int getRowCount(){
          return this.rowCount;
     public String getData(int row, int column){
          return this.results[row][column];
     public boolean doResultsExist(){
          return this.resultsExist;
} // end of database InterfaceI developed this code about a year ago and maybe it is time to simplify it.
With MySql I could create an instance of Database Interface or use one of its subclasses and perform any function on the database by calling its methods.
maybe it is time for a redesign!
thanks
jim