Dynamic where clauses lambda or query in C#

Question

I am trying to write a dynamic lambda or query but it occurs an error..

for lambda; I created a function

    public IEnumerable<musteriler>  GetCustomers<musteriler>(Expression<Func<musteriler, bool>> where)
   {
    IEnumerable<musteriler> _musteriler = market.musteriler.Where(where).Select(m => m);

     return _musteriler;

    }

and I call like that

  IEnumerable<musteriler> _musteriler  = helper.GetCustomers<musteriler>(m => m.MAktif == true);

I get two errors in Where(where) which are

    The best overloaded method match for System.Data.Objects.ObjectQuery<AkilliMarket.musteriler>.Where(string, params System.Data.Objects.ObjectParameter[])' has some invalid arguments

and

   Argument 1: cannot convert from 'System.Linq.Expressions.Expression<System.Func<musteriler,bool>>' to 'string'

after I tried a string query like

 IEnumerable<musteriler> _musteriler=  market.musteriler.Where("MAktif = true").Select(m => m) as IEnumerable<musteriler>;

yes it works but I cant use _musteriler.. for example when I write _musteriler.Count(); I get this error

  'MAktif' could not be resolved in the current scope or context. Make sure that all referenced variables are in scope, that required schemas are loaded, and that namespaces are referenced correctly. Near simple identifier, line 6, column 1.

MAktif is a column name of my musteriler table in db. and I tried another columns but result is same..

Where are my mistakes for both?

market is my database which connected datamodel. and i defined it as private AkilliMarketEntities market; — unbalanced
– unbalanced, Commented Jun 13, 2012 at 12:04

Eren Ersönmez · Accepted Answer · 2012-06-13 12:54:37Z

1

The problem is IQueryable<T>.Where is an extension method and ObjectQuery.Where is picked as "best overloaded method match" before extension methods are considered.

Try:

public IEnumerable<AkilliMarket.musteriler> GetCustomers<AkilliMarket.musteriler>(Expression<Func<AkilliMarket.musteriler, bool>> predicate)
{
   return market.musteriler.AsQueryable().Where(predicate);
}

edited Jun 13, 2012 at 12:54

answered Jun 13, 2012 at 11:58

Eren Ersönmez

39.2k8 gold badges76 silver badges94 bronze badges

Sign up to request clarification or add additional context in comments.

8 Comments

unbalanced Over a year ago

similar error Error 1 The best overloaded method match for 'System.Data.Objects.ObjectQuery<AkilliMarket.musteriler>.Where(string, params System.Data.Objects.ObjectParameter[])' has some invalid arguments Error 2 Argument 1: cannot convert from 'System.Func<musteriler,bool>' to 'string'

Eren Ersönmez Over a year ago

Do you have using System.Linq like @Ladislav suggested?

unbalanced Over a year ago

yes I have... my all references are using System; using System.Collections.Generic; using System.Linq; using System.Text;

unbalanced Over a year ago

no again... Error 2 Argument 2: cannot convert from 'System.Func<musteriler,bool>' to 'System.Func<AkilliMarket.musteriler,int,bool>' Error 1 'System.Collections.Generic.IEnumerable<AkilliMarket.musteriler>' does not contain a definition for 'Where' and the best extension method overload 'System.Linq.Enumerable.Where<TSource>(System.Collections.Generic.IEnumerable<TSource>, System.Func<TSource,int,bool>)' has some invalid arguments

Hans Keﬆing Over a year ago

Do not use AsEnumerable() here, use AsQueryable(). AsEnumerable will cause the whole table to load into memory, before applying the "Where()".

|

Raphaël Althaus · Accepted Answer · 2012-06-13 12:37:50Z

1

public IEnumerable<musteriler>  GetCustomers<musteriler>(Expression<Func<musteriler, bool>> predicate)
       {
        return market.musteriler.AsQueryable().Where(predicate).AsEnumerable();

        }

if it doesn't work

can you just try

 var _musteriler=  market.musteriler.Where("it.MAktif = @val", new ObjectParameter("val", true)).AsEnumerable().Count();

and if it works, your method should be (if there's still a sense to make a method)

public IEnumerable<musteriler> GetCustomers(string whereClause, params ObjectParameter[] parameters) {
   return market.musteriler.Where(whereClause, parameters).AsEnumerable(); 
}

edited Jun 13, 2012 at 12:37

answered Jun 13, 2012 at 12:00

Raphaël Althaus

60.6k6 gold badges106 silver badges127 bronze badges

3 Comments

unbalanced Over a year ago

thank for your nice answer but I get same error. because the problem is not about return type.. it shows problem is in predicate.. and same error which I post in my first message

unbalanced Over a year ago

using System; using System.Collections.Generic; using System.Linq; using System.Text;

unbalanced Over a year ago

thank you Raphael, your second code works too :) thank you very much for your interesting..

Ladislav Mrnka · Accepted Answer · 2012-06-13 12:05:48Z

0

I guess you need to add this at the beginning of your code:

using System.Linq;

It looks like your market is ObjectContext and musteriler is ObjectSet and it doesn't provide Where accepting lambda - you need extension Where method on IQueryable which accepts lambda expression.

answered Jun 13, 2012 at 12:05

Ladislav Mrnka

365k60 gold badges666 silver badges673 bronze badges

1 Comment

unbalanced Over a year ago

yest market is an objectcontext.. and could you give me a sample for it ?

Harry N · Accepted Answer · 2016-12-22 17:47:10Z

-1

In the example I was trying , I was getting the error,

No overload for method 'Where' takes 3 arguments

with my where clause expression using SQLParametera.

I found that I needed

using System.Linq.Dynamic; once I discovered it, DUH

answered Dec 22, 2016 at 17:47

Harry N

1

1 Comment

Servy Over a year ago

This has nothing to do with the question asked here.

Collectives™ on Stack Overflow

Dynamic where clauses lambda or query in C#

4 Answers 4

8 Comments

3 Comments

1 Comment

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

8 Comments

3 Comments

1 Comment

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related