Linq在查询中使用TakeWhile

Question

Hi i just started learning linq and have been trying to understand the TakeWhile usage

here i have tried something like this

 using (  var db = new OrchestrateDataEntities())
        {


            var y = db.Set<Rulebook_Mapping>();
            var xyz = y.TakeWhile(x => x.ID == 2).AsQueryable();
            foreach (var item in xyz)
            {
                Console.WriteLine(item.ID);


            }

        }
        Console.ReadKey();

and then comes the error

 LINQ to Entities does not recognize the method 'System.Linq.IQueryable`1[ConFW.Rulebook_Mapping] TakeWhile[Rulebook_Mapping](System.Linq.IQueryable`1[ConFW.Rulebook_Mapping], System.Linq.Expressions.Expression`1[System.Func`2[ConFW.Rulebook_Mapping,System.Boolean]])' method, and this method cannot be translated into a store expression.

Answer 1

Check supported and unsupported methods in LINQ to Entity at http://blogs.msdn.com/b/wriju/archive/2009/01/02/linq-to-entity-skip-and-take-method-does-not-work.aspx . Then open paging method page, you will see that TakeWhile is not supported (at the bottom).

Answer 2

qxg is right , TakeWhile is not implemented by EF, but you can use it in LINQ to Object.

Old code:

var y = db.Set<Rulebook_Mapping>();

New code:

var y = db.Set<Rulebook_Mapping>().ToList();

New code should fix the error, it brings all records in RuleBook_Mapping table to local memory, if possible add where filter before ToList() will help the performance.