SysMultiTableLookup for Multiple lookup fields from multiple tables

   public void lookup()

   {

    SysMultiTableLookup  sysMultiTableLookup;
    Query                query;
    QueryBuildDataSource queryBuildDataSource,qbds1;
    QueryBuildRange      qbr;
    VendTable            vendtable;
    DirPartyTable        dirPartyTable;
    super();

 
    query = new Query();
    queryBuildDataSource = query.addDataSource(tableNum(VendTable));
    qbds1                =  queryBuildDataSource.addDataSource(tablenum(DirPartyTable));
    qbds1.relations(true);

    sysMultiTableLookup =   SysMultiTableLookup::newParameters(VendorAcc,query);
   //vendorAcc is control name

    sysMultiTableLookup.addLookupfield(fieldNum(VendTable,AccountNum),1);
    sysMultiTableLookup.addLookupfield(fieldNum(dirPartyTable,Name),2);

    sysMultiTableLookup.parmQuery(query);
    sysMultiTableLookup.performFormLookup();
}

Multiple Custom Lookups Using SysTableLookup On Dialog Class And Filtering Second Lookup using First Lookup value

// Create Dialog Class and extend it with RunBase

class CustomDialog extends RunBase
{

    CustTable           custTable;
    SalesLine           salesLine;
    SalesTable          salesTable;
    CustAccount         custAccount;
    SalesId             salesId;

    Dialog              dialog;

    DialogField         fieldAccount, SalesOrders, Items;
    FormStringControl   control1, control2, control3;

}

//Create an Override Method Dialog

protected Object Dialog()
{

    dialog = super();

    // Set a title for dialog
    dialog.caption( 'Simple Dialog');

    // Add a new field to Dialog
    fieldAccount = dialog.addField( extendedTypeStr(AccountNum), 'Customer account' );
    control1     = fieldAccount.control();

    SalesOrders  = dialog.addField(extendedTypeStr(salesId), "Sales Orders");
    control2     = SalesOrders.control();
//
    Items        = dialog.addField(extendedTypeStr(itemId), "Items");
    control3     = items.control();

    control1.registerOverrideMethod(methodStr(FormStringControl, lookup), methodStr(CustCreateDialog, Accountlookup), this);

    control2.registerOverrideMethod(methodStr(FormStringControl, lookup), methodStr(CustCreateDialog, OrdersLookup), this);
    control3.registerOverrideMethod(methodStr(FormStringControl, lookup), methodStr(CustCreateDialog, ItemsLookup), this);

    return dialog;
}

// Create Lookup For FieldAccount Dialog Field

private void AccountLookup(FormStringControl    _control)

{

    SysTableLookup          sysTableLookup = new SysTableLookup() ;

    QueryBuildDataSource    qbds1;

    Query                   query = new Query();

    qbds1 = query.addDataSource(tablenum(SalesLine));

    sysTableLookup = SysTableLookup::newParameters(tablenum(SalesLine), _control );

    sysTableLookup.addLookupfield(fieldnum(SalesLine, CustAccount));

    SysTableLookup.parmQuery(query);

    SysTableLookup.performFormLookup();

}

// Create Lookup For SalesOrders Dialog Field

private void OrdersLookup(FormStringControl _control)

{

    SysTableLookup          sysTableLookup = new SysTableLookup() ;

    QueryBuildDataSource    qbds1;

    QueryBuildRange         range;

    Query                   query = new Query();

    qbds1 = query.addDataSource(tablenum(SalesLine));

    range = qbds1.addRange(fieldNum(SalesLine, CustAccount));

    range.value(queryValue(fieldAccount.value()));

    sysTableLookup = SysTableLookup::newParameters(tablenum(SalesLine),_control);

    sysTableLookup.addLookupfield(fieldnum(SalesLine, salesId));

    SysTableLookup.parmQuery(query);

    SysTableLookup.performFormLookup();

}

// Create Lookup For Items Dialog Field

private void itemsLookup(FormStringControl  _control)

{

    SysTableLookup          sysTableLookup = new SysTableLookup() ;

    QueryBuildDataSource    qbds1;

    QueryBuildRange         range;

    Query                   query = new Query();

    qbds1 = query.addDataSource(tablenum(SalesLine));

    range = qbds1.addRange(fieldNum(salesTable, salesId));

    range.value(queryValue(SalesOrders.value()));

    sysTableLookup = SysTableLookup::newParameters(tablenum(salesLine),_control);

    sysTableLookup.addLookupfield(fieldnum(SalesLine, ItemId));

    SysTableLookup.parmQuery(query);

    SysTableLookup.performFormLookup();

}

//Create Run method if you want to execute any logic

public void run()

{

    // Set Dialog field value to find SalesLine

    salesLine = salesLine::find("000003");

    if (salesLine)

    {

        // Shows retrieved information

        info( strFmt('%1 -- %2' , salesLine.custaccount, salesLine.salesid));

    }

    else

    {

        error( 'Customer Account not found!');

    }

}

//Create Main()

public static void main(Args _args)

{

    CustomDialog custCreate = new CustomDialog();

    // Prompt the dialog, if user clicks in OK it returns true

    if (custCreate.prompt())

    {

        custCreate.run();

    }

}