[Kde-java] A curious problem with QSqlCursor

[Richard Dale]

On Monday 25 October 2004 09:26, David Goodenough wrote:
> Richard,
>
> I have been working further with the java interface, and I have hit a
> problem and I am not quite sure how to proceed.
>
> According to the Qt SQL documentation in order to get a calculated field
> into a QDataTable or QDataBrowser you have to subclass QSqlCursor
> and in the constructor of the subclass append the new fields and set
> them as calculated and then have a calculateField method which
> does the calculation.
>
> This is all described in http://doc.trolltech.com/3.3/sql.html
>
> This I did:-
>
> public class ChargeCursor extends QSqlCursor {
>  public ChargeCursor() {
>   super( "charges");
>   setMode( ReadOnly); // we only read data through this cursor
>   QSqlFieldInfo vat = new QSqlFieldInfo( "vat", QVariant.Double);
>   vat.setCalculated( true);
>   append( vat);
>   QSqlFieldInfo total = new QSqlFieldInfo( "total", QVariant.Double);
>   total.setCalculated( true);
>   append( total);
>   }
>  public QVariant calculateField( String name) {
>   System.out.println( "Calculating field " + name);
>   if( "vat".equals( name))
>    {
>     double price = value( "price").toDouble( );
>     double vatrate = value( "vatrate").toDouble( );
>     return new QVariant( price * vatrate);
>     }
>    else if( "total".equals( name)) {
>     double price = value( "price").toDouble( );
>     double vatrate = value( "vatrate").toDouble( );
>     return new QVariant( price * ( 1 + vatrate));
>     }
>   return new QVariant( ( String)null);
>   }
>  }
>
> When I try to use this subclassed cursor however it does not seem to be
> calling the calculateField method and when you use somthing like the
> QDataTable.refresh method a dialog pops up complaining that charges.vat
> does not exist.
>
> When I come to use the ChargeCursor even simply getting the value does
> NOT seem to call calculateField (which you will notice has a debug line in
> it above).
>
>   cursor = new ChargeCursor( );
>   System.out.println( "cursor.value( 'vat') = " + cursor.value( "vat"));
>   chargesTable.setSqlCursor( cursor, false, false);
>   System.out.println( "Set SqlCursor");
>   chargesTable.setColumn( 0, "item", "Item");
>   chargesTable.setColumn( 1, "quantity", "Quantity");
>   chargesTable.setColumn( 2, "description", "Description");
>   chargesTable.setColumn( 3, "price", "Price");
>   chargesTable.setColumn( 4, "vat", "VAT");
>   chargesTable.setColumn( 5, "due", "Due Date");
>   chargesTable.setColumn( 6, "total", "Total");
>   chargesTable.setFilter( "customer = '" + customer + "' AND invoice =
> ''"); String[ ]sort = { "due DESC" };
>   chargesTable.setSort( sort);
>   chargesTable.refresh( );
>
> It is at this point (the call to refresh) when the message about column
> charges.vat does not exist comes up.
>
> I have checked that the calculatedField attribute is being properly set.
>
> So my question is, where do I start looking for why the callback is not
> being called?
It will be in the QSqlCursor.cpp code. I've just had a look, and there aren't 
any virtual method callbacks. At the moment only subclasses of QObject have 
callbacks, and then not all of them. The next version of the java bindings 
based on the Smoke library, and generated by the '-fjava' option to kalyptus 
will have all possible callbacks. The code generated by the '-fjni' option is 
a bit limited. It would be possible to add more callbacks on an 'ad hoc' 
basis though.

-- Richard