Filter form's main datasource through the linked datasource

I have a custom form which has two datasouces. Lets say to make it easer that my form has the Salestable and SalesLines datasources.

for example I could say that I have a filter which is bounded with the ItemGroup edt .

I want to filter the SalesTable Datasource through this filter in order to 'show' in a grid which is connected with the SalesOrders datasouce :

''all SalesOrders which 'have' saleslines with saleslines.ItemGroup == somethingfromFilter''.

Whatever I tried is faild. Can someone help me?

FYI: the datasources properties I asume that are proper linked: SalesLine.JoinSource = SalesTable All of my tries was in modified method of the filter.

Solution

I will assume you have an ItemGroupId field in the SalesLine table. This is not standard.
Also I will assume you have a filter field in the form called ItemGroupIdCtrl.

Add a helper datasource SalesLineEx:

Name: SalesLineEx
Table: SalesLine
Allow...: No
JoinSource: SalesTable
LinkType: ExistJoin

In the SalesTable datasource executeQuery modthod:

public void executeQuery()
{
    SysQuery::findOrCreateRange(salesLineEx_ds.queryBuildDataSource(), fieldNum(SalesLine,ItemGroupId)).value(ItemGroupIdCtrl.text());
    salesLineEx_ds.queryBuildDataSource().enabled(ItemGroupIdCtrl.text() != '');
    super();
}

This will check the existence of sales lines with a matching field if the filter field has a value. If no value is entered the filtering datasource is disabled.

Most likely you will want to research after change of filter value:

public boolean modified()
{
    boolean ret = super();
    salesTable_ds.executeQuery();
    return ret;
}