In my previous post, I introduced my problem, but I didn’t explain the problem with Entity Framework

When you try the solution indicated you will take the following error:

LINQ to Entities don’t recognize the method 'System.String Join(System.String, System.Collections.Generic.IEnumerable`1[System.String])’ of the method, and this method can’t be translated into a stored expression.

The query that produces that error was:

   1: var consulta = (from TCabecera cab in 

   2:                  contexto_local.TCabecera  

   3:    let Detalle = (from TDetalle detalle 

   4:                    in cab.TDetalle 

   5:    select detalle.Nombre)    

   6:    let Nombres = string.Join(",",Detalle )     

   7:    select new   

   8:       {  

   9:        cab.Campo1, 

  10:        cab.Campo2, 

  11:        Nombres

  12:        }).ToList();

  13: grid.DataSource=consulta;

 

Why is this error happening?

This error happens when the query couldn’t be translated into T-SQL.

Solutions?

To quit that error, we need to execute the query on 2 steps:

   1: var consulta = (from TCabecera cab in   

   2:                 contexto_local.TCabecera    

   3:       let Detalle = (from TDetalle detalle   

   4:                      in cab.TDetalle   

   5:                      select detalle.Nombre)      

   6:      select new     

   7:       {    

   8:         cab.Campo1, 

   9:         cab.Campo2,  

  10:         Detalle 

  11:         }).ToList();  

  12: var consulta2 = (from dato in consulta

  13:             let Nombes = string.Join(",",dato.Detalle)

  14:             select new 

  15:             {

  16:             dato.Campo1,

  17:             dato.Campo2,

  18:             Nombres

  19:             };

  20:         grid.DataSource=consulta2.ToList();

Curiously

This problem happens with Entity Framework but, the same problem can’t be reproduced on LINQ – To – SQL, that it works fine in one unique step.

Hope It’s helpful

Best Regards