How to create a Generic lambda expression. Many of my entities perform the same Lambda expression predicate.

Question

I use Entity Framework 4.
How can I perform a Generic Where Lambda Clause.?

I Have many Entity that need the same Where Query.

public Func<SupplierTypeText, bool> GetLmbLang()
{
    return (p => p.LangID == 1);
}


public Func<ProductText, bool> GetLmbLang()
{
    return (p => p.LangID == 1);
}


public Func<CategoryText, bool> GetLmbLang()
{
    return (p => p.LangID == 1);
}

I would like to have a generic method like

//public interface IRepository<T> : IRepository<T> where T : class
public Func<T, bool> GenericGetLmbLang()
{
    return (p => p.LangID == 1);
}

For the moment, I hardcoded Language ID == 1, that will be from the user session to make it dynamic.
That's would be very usefull if I Can directly call the GetLmbLang() Directly in the Where clause.

 var ViewModel = _db.Suppliers.Select(model => new
            {
                model,
                SupType = _db.SupplierTypeTexts.Where(a => GenericGetLmbLang())
            });

------UPDATE--------
Here is what I Trying and nothing works.

My Base Class

 public class BaseGenericModel
    {
        public int LangID { get; set; }

        public Func<BaseGenericModel, bool> GetLmbLang()
        {
            return (p => p.LangID == 1);
        }

    }

My interface is

   public interface IBaseRepository<T> where T : BaseGenericModel
   {
        Func<T, bool> GetLmbLang();
   }


   public class BaseRepository<T> : IBaseRepository<T> where T : BaseGenericModel
   {

       public Func<T, bool> GetLmbLang()
       {
          return (p => p.LangID == 1);
       }
   }

I Can't call this repository form my SupplierTypeText,ProductText,CategoryText. That's doesn't work.

Answer 1

It seems that you have three different types all having the LangID property. I would make them derive from a common base class where this property is defined:

public class BaseClass
{
    public int LangID { get; set; }
}

and then have a single method:

public Func<BaseClass, bool> GetLmbLang()
{
    return (p => p.LangID == 1);
}

An interface containing this property could also be used.

If you want to make it generic you could but you will still need a generic constraint to indicate a common base type if you want to use the LangID property:

public class SomeRepository<T> where T: BaseClass
{
    public Func<T, bool> GetLmbLang()
    {
        return (p => p.LangID == 1);
    }
    ...
}