Question

I have LINQ statement that looks like this:

return ( from c in customers select new ClientEntity() { Name = c.Name, ... }); 

I’d like to be able to abstract out the select into its own method so that I can have different ‘mapping’ option. What does my method need to return?

In essence, I’d like my LINQ query to look like this:

return ( from c in customers select new Mapper(c)); 

Edit:

This is for LINQ to SQL.

Answer 1

New answer now I’ve noticed that it’s Linq to SQL… 🙂

If you look at the version of Select that works on IQueryable<T> it doesn’t take a Func<In, Out>. Instead, it takes an Expression<Func<In, Out>>. The compiler knows how to generate such a thing from a lambda, which is why your normal code compiles.

So to have a variety of select mapping functions ready to use by passing them to Select, you could declared them like this:

private static readonly Expression<Func<CustomerInfo, string>> GetName = c => c.Name;  private static readonly Expression<Func<CustomerInfo, ClientEntity>> GetEntity = c => new ClientEntity { Name = c.Name, ... }; 

You would then use them like this:

var names = customers.Select(GetName);  var entities = customers.Select(GetEntity);