how to add schema to TableRow

[Aniruddh Sharma]

I want to do some SQL transforms on following collection

PCollection<TableRow> allData =
                p.apply(tab, BigQueryIO.readTableRowsWithSchema()               
         
                        .from(optionsFromDB.get("stdBQTable"))
                        .withMethod(BigQueryIO.TypedRead.Method.DIRECT_READ)
                        .withSelectedFields(Cols))

But I get error - no schema attached , although I am reading with 
RowsWithSchema.

Can you please give some example what to call to explicitly attach schema to 
this.