Hmm, what I did for a similar use-case was creating a new field called: product_search_as_you_type of the type: search_as_you_type.
And then for lineDescription, i would use copy_to: with the value: product_search_as_you_type.
In this case all the lines of the product will be copied to that field and you can search all the contents of the object without worrying about not using that field later in a different kind of way.