LINQ到实体，使用类似SQL的操作符

I have a LINQ to ENTITY query that pulls from a table, but I need to be able to create a "fuzzy" type search. So I need to add a where clause that searches by lastname IF they add the criteria in the search box (Textbox, CAN be blank --- in which case it pulls EVERYTHING).I have a LINQ to ENTITY query that pulls from a