Re: numeric type

[tivvpgsqljdbc(at)gtech-ua(dot)com]

Peter написав(ла):
> > > Long story. We're migrating old Access app to Postgres but still need 
> > > to be able to exchange datasets with the old app users (app supports 
> > > it's own import/export in MDB format). Since migration is expected to 
> > > last several years we need some sort of automated PG->MDB thing.
> > >
> > >       
> > Why don't you just make you converter configurable on how it handles 
> > decimal without specs?
> >     
>
> I would need to hack Jackcess library in order to do that... besides it does
> not seem the proper way to do it, more like an ugly hack. getPrecision and
> getScale are supposed to return the true precision and scale after all...
>
> Peter
>
>   
It may be easier to write a wrapper over JDBC driver doing needed 
conversion. With Java Proxy it is not a complex task.
It may look much like the next:
public class DelegatingHandler<TP> implements InvocationHandler {
   protected final TP parent;

   public DelegatingHandler(TP parent) {
       this.parent = parent;
   }

   public Object invoke(Object proxy, Method method, Object[] args) 
throws Throwable {
           Method override = 
this.getClass().getMethod(method.getName(), method.getParameterTypes());
           if (override != null)
               return override.invoke(this, args);
           return method.invoke(parent, args);
       }
}

public class ConnectionWrapper extends DelegatingHandler<Connection> {

   public static Connection makeConnectionWrapper(Connection connection) {
       return (Connection) 
Proxy.newProxyInstance(ConnectionWrapper.class.getClassLoader(),
           new Class[]{Connection.class}, new 
ConnectionWrapper(connection));
   }
...
   public PreparedStatement prepareStatement(String sql) throws 
SQLException {
       return makePreparedStatementWrapper(parent.prepareStatement(sql));
   }
...
}


You simply create a wrapper and "override" needed methods by making 
methods in wrapper with exactly same name and signature, calling parent 
instead of super when needed.