Right-click the Chapter8Model.edmx file and select Open With.

Select XML Editor.

Find the following section:

<edmx:ConceptualModels>
      <Schema Namespace="BookModel" Alias="Self"
xmlns:annotation="http://schemas.microsoft.com/ado/2009/02/edm/annotation"
xmlns="http://schemas.microsoft.com/ado/2008/09/edm">

Add the following inside the previous section:

<Function Name="LongFilmDescription" ReturnType="Edm.String">
    <Parameter Name="Film" Type="BookModel.Film">
    </Parameter>
    <DefiningExpression>
      Trim(Film.Title) + " " + Film.Description
    </DefiningExpression>
</Function>

Open Program.cs and add the following using directive:

using System.Data.Objects.DataClasses;

Unfortunately, L2E doesn't yet know about the LongFilmDescription function, so we have to tell it by creating a static class decorated with the [EdmFunction] attribute to allow us to access it. Add the following code in Program.cs:

public static class MDF
{
    [EdmFunction("BookModel", "LongFilmDescription")]
    public static string LongFilmDescription(Film f)
    {
        throw new NotSupportedException("This function can only be used in a query");
    }
}

Once this is done, you can now utilize your function in L2E queries as follows:

var query = from f in ctx.Films
select new { FullName = MDF.LongFilmDescription(f) };