Custom extension function in select statment of an EF query - entity-framework

Question

In our database we have a table that looks like this which we have mapped to an entity in our Database-First EF model:
CREATE TABLE Texts(
Id integer,
Eng nvarchar(max),
Nob nvarchar(max),
...
)
A row in this table may be quite large, so we only want to get the value of the column that is currently need by a language selection the user has done.
My idea was to have an extension function to do it for me, but I dont have any idea nor can't find any way to write it (if it is even possible). I have tried a few variants, but (obviously) it failed with an exception that states that it cannot be translated into a store expression. So I am a bit stuck.
The idea of usage for this function is:
context.Codes.Where(row => row.Id == 234).Select(row => new {
row.Id,
Text = Text.GetLocalizedText("Eng") // This should generate an SQL that only retrieves the Eng
// column of the Text navigation property (which is
// connected to the Texts table.
});
That should generate a select similar to this (which are similar to the example above except using Text.Eng directly):
SELECT
[Extent1].[Id] AS [Id],
[Extent2].[Eng] AS [Eng]
FROM [dbo].[Codes] AS [Extent1]
INNER JOIN [dbo].[Texts] AS [Extent2] ON [Extent1].[TextId] = [Extent2].[Id]
WHERE 234 = [Extent1].[Id]
Does anyone know if this is possible, and if it is; how to write it? If it isn't possible, does anyone have any other idea on how to solve this without retrieving the whole Text entity with all of it's columns?

Answer 1

An extension method of IQueryable<Code> would work but it is not as flexible as you probably want to have it because you would need to have an extension per type of projection you want to perform and you cannot work with an anonymous result object.
The idea is basically like so:
You need a named class (instead of anonymous) which you can project into:
public class CodeData
{
public int Id { get; set; }
public string LocalizedText { get; set; }
}
And then an extension method with the language parameter:
public static class CustomExtensions
{
public static IQueryable<CodeData> SelectCodeData(
this IQueryable<Code> query, string language)
{
switch (language)
{
case "Eng":
return query.Select(code => new CodeData
{
Id = code.Id,
LocalizedText = code.Text.Eng
});
case "Nob":
return query.Select(code => new CodeData
{
Id = code.Id,
LocalizedText = code.Text.Nob
});
//... more languages
}
throw new ArgumentException("Invalid language code.", "language");
}
}
Then it can be called like this:
using CustomExtensions;
// ...
IQueryable<CodeData> codeDataQuery = context.Codes
.Where(row => row.Id == 234)
.SelectCodeData("Eng");