Review of child table selection using extension table framework

To continue with table extension framework topic let's review how it tries to fetch dependent table from main:

• From dependent DataSource on form. Only heaving taught join like outer/inner. Delayed will not work, however you can still fix that using SysExtensionSerializerFormRunHelper class
  
• Joined datasource in selection like select ... join or Query class
• From field PackedExtensions at parent table
  
• Fetching from DB

You can find the logic of child table fetching in SysExtensionSerializerMap::getExtensiontable method:

You can set breakpoints here and using project from first post related to extension tables and following job ensure that it behaves as expected.

static void TableExtensionFetch(Args _args)
{
    TableExtensionParent    parent;
    TableExtensionChild     child,
                            child2;

    Query                   q = new Query();
    QueryBuildDataSource    qbdsParent,
                            qbdsChild;
    QueryRun                qr;

    FormRun                 formRun;
    Object                  formRunObject;
    Args                    args = new Args();

    // Form DataSource
    args.name(formstr(TableExtensionForm));
    formRun = ClassFactory.formRunClass(args);
    formRun.init();
    formRun.run();
    formRun.wait();
    if (formHasMethod(formRun, identifierStr(getParentTable)))
    {
        formRunObject       = formRun;
        parent              = formRunObject.getParentTable();
        child               = parent.tableExtensionChild();
    }

    parent = null;
    parent.clear();
    child.clear();
    child2.clear();

    // Joined table 1
    select firstonly parent
        join child
            where child.TableExtensionParent == parent.RecId;

    child2 = parent.tableExtensionChild();


    parent.clear();
    child.clear();
    child2.clear();
    
    // Joined table 1
    qbdsParent  = q.addDataSource(tableNum(TableExtensionParent));
    qbdsParent.firstOnly(true);
    qbdsChild   = qbdsParent.addDataSource(tableNum(TableExtensionChild));
    qbdsChild.relations(true);

    qr = new QueryRun(q);
    while (qr.next())
    {
        parent  = qr.get(tableNum(TableExtensionParent));
        child   = parent.tableExtensionChild();
    }

    parent.clear();
    child.clear();
    child2.clear();

    // packed
    child.AdditionalField = 'packed';
    parent.packTableExtensionChild(child);
    child2 = parent.tableExtensionChild();

    parent.clear();
    child.clear();
    child2.clear();
    
    // DB
    select firstonly parent;
    child = parent.tableExtensionChild();

    abs(1);
}

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