Run-time add/remove datasource to filter results

Sometimes I add a Combobox above a Grid to give the user several 'canned' filters.

In some cases I would like to filter on a table other than the one displayed in the grid.  For example, I might want to filter a grid of CustTable records based on related Address table records.

If you want the filter to be active all the time, you can just add the filtering datasource to your form.  But if you only want the filter to be active some of the time, you need to be able to dynamically (run-time) add and remove the datasource that does the filtering.

The code below shows how to dynamically add and remove (actually disable) a child datasource for filtering purposes.

public void executeQuery() //on form datasource "formDatasourceName"
{
    QueryBuildDataSource    qbds;
    ;
 
    if(this.query().dataSourceName("formDatasourceName").childDataSourceCount() == 1)
    {
        //if the filter datasource has been added in the past (prior run of executeQuery), disable it
        this.query().dataSourceName("formDatasourceName").childDataSourceNo(1).enabled(false);
    }

    if (booleanFilterResults)
    {
        //this creates a "hidden" exists join to act as a filter
        if (this.query().dataSourceName("formDatasourceName").childDataSourceCount() == 1)
        {
            //if the filter datasource
            qbds = this.query().dataSourceName("formDatasourceName").childDataSourceNo(1);
            qbds.enabled(true);
        }
        else
        {
            qbds = this.query().dataSourceName("formDatasourceName").addDataSource(tablenum(filterTableName));
        }

        qbds.clearRanges();

        qbds.relations(true);  //or use .addLink...
        qbds.joinMode(JoinMode::ExistsJoin);
        qbds.fetchMode(queryfetchmode::One2One);
        
        //filter on some value, in this case a comboBox selection.  
        //Of course you'll call formDatasourceName.executeQuery() in comboBoxFilter modified method
        qbds.addRange(fieldnum(filterTableName, ItemId)).value(queryValue(comboBoxFilter.valueStr()));
    }

    super();
}