Filter a lookup field based on the other lookup field selected value

Hello, 

I have a case to filter a lookup field based on the other lookup field value 

lets consider I have two lookup fields A and B and I have A1, A2 items in 'A' Lookup. 

I have B1, B2, B3, B4 in B lookup.

Now I wanted to filter B1 and B2 from lookup 'B' If i have chosen A1from A lookup.

and B3, B4 If I have chosen A2 from A lookup  

I tried using crt.LoadDataRequest in crt.HandleViewModelAttributeChangeRequest handler on change of A lookup. But it could not find the datasource of the lookup B on changing Lookup A, and it could not able to filter the lookup even in page load.

Any suggestions are really helpful.

Thanks

Gargeyi