error to customise filter on ProductName

i want to filter my Product Name in my BOM lines , Form: :"BOMConsistOf "

                                         table is "BOM" & ItemName is actually data method not  a field . here  in the below code am getting error in 3rd last line i.e( qb1.addlink(fieldnum( .......   )))

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public void context()

{

int selectedMenu;

formrun fr;

Args ag;

Name strtext;

querybuilddataSource qb1;

queryrun qr; query q; PopupMenu menu = new PopupMenu(element.hWnd());

int a = menu.insertItem('Filter By Field');

int b = menu.insertItem('Filter By Selection');

int c = menu.insertItem('Remove Filter');

;

selectedMenu = menu.draw();

switch (selectedMenu)

{

case-1: break;

case a: ag = new args('SysformSearch');

fr = new formrun(ag);

fr.run();

fr.wait();

strtext = fr.design().controlName('FindEdit').valueStr();

if(strtext) { q = BOMVersion_ds.query(); qb1= q.dataSourceTable(tableNum(BOM));

qb1= qb1.addDataSource(tableNum(EcoResProductTranslation)); qb1.addLink(fieldNum(BOM,ItemName),fieldNum(EcoResProductTranslation ,Name)); qb1.addRange(FieldNum(EcoResProductTranslation,Name)).value(strtext);

BOM_ds.query(Q); BOM_ds.executeQuery(); }