[Solved]-LINQ to Entities does not recognize the method-LINQ,C#

probably linq-to-entities doesn't support the code which you've written in productbymodelequalitycomparer. you can call asenumerable before calling distinct, this will make distinct executed via linq-to-objects but it won't be iqueryable anymore:

var enumerable = query.asenumerable().distinct(new productbymodelequalitycomparer()); return query; }