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Using Entity Framework 4.1 what is the best way to map an auto generated entity framework entity to an object suitable for Data Transfer?

What i'm working with looks like this:

WPF Application -> WCF Service -> Entity Framework (DAL) -> Database

The WPF application could be swapped out to an ASP.NET website at some point in addition to the WPF Application. Hence the use of a WCF service.

The WCF Service, Database and Entity Framework code will all sit on the same physical tier.

In previous versions of Entity Framework (Before 4.0) I believe you had to write your own mapping code for your classes. Is there a better way to do this now?

Also an additional question is would it be bad practice to include methods on the DTO's that performs business logic? Where would be the best place to apply business logic in this case?

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The best way to map from EF entities to DTOs is to project. My example linked there uses view models rather than DTOs, but the idea is the same.

With most ORMs, EF included, there is a cost to materializing entities which you don't need to pay if you just need a DTO. The cost includes:

  • Fixup -- when two objects reference the same related object, make sure they point to the same instance.
  • Tracking -- overhead for tracking the instance in a context.
  • Unnecessary columns -- you might not need all properties for your DTOs.
  • Aggregates -- functions like .Count() are far more efficient in SQL than in object space.

If you use a L2E projection, you don't incur any of this cost. If you follow the common advice to use the AutoMapper hammer for every problem which looks like a nail, you pay all of it.

I do agree with @sternr about not putting methods on entities / DTOs. For a more detailed examination of this idea, read "At the Boundaries, Applications are Not Object-Oriented."

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Use AutoMapper to map between simple DTO's and EF entities

[EDIT:] for your other questions:

For the mapping: you could either use the built in edmx designer which allows you to use an existing DB schema to generate your model entities, or the other way around (define your entities, and let EF create your DDL).
Newer versions (as of 4.1) you could simply code your entities and add DataAnnotations on the associated properties and EF will do the magic mapping (here's a good sample)

As for adding logic to DTO's, well DTO's by their definition are a data contact - the consumer will probably create it's own implementation of them (be them by the automatic proxy or other manual wrappers), so placing logic in them kinda makes no sense.

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AutoMapper is indeed very nice and I would also recommend you to take a look at the excellent article published on Sam's Code blog. He's using T4 templates to auto-generate the DTOs and the mapping configuration for AutoMapper. He has since released the code as project loef on codeplex.
AutoMapper is a terrible tool for going from EF entities to DTOs because it does not support IQueryable or EF projections. Agreed about methods.

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