when should i use a datacontract and when a messagecontract in WCF

Question

ON what basis should we decide whether we have to create a dataContract or a MessageContract for my WCF services.

What I know is that when we need to have more control over SOAP,We use MessageContract.

Secondly I have seen some code in which DataContract is exposed through MessageContract.Whats the use of it.

Please provide some real life scenerios.

Answer 1

If you need to take over the SOAP headers and body explicitly, you would use MessageContracts. For example, if you needed to make sure a credit card number was encrypted in your message separately from the rest of your type, you'd need to get that level of control over the message on the wire.

Here's more information on that with some examples (specifically the encryption example): http://msdn.microsoft.com/en-us/library/ms730255.aspx

If you just want pure DTOs and don't care about their shape on the wire, go with DataContracts.

Answer 2

It's not an "either-or" question - you'll always have data contracts if you're dealing with compound data (more than just the basic types of int, string etc.). That's a given.

You'll only ever need message contracts if you need to very closely and very specifically control the layout of your SOAP messages. In most case, over 90% of the time - you don't.

A message contract allows you to specifically say which elements (scalar types or compound types as DataContracts) will be in the SOAP header, and which will be in the SOAP body.

You might need this if you have a communication partner which requires a very specific format and you have to tweak your SOAP messages to match that given layout exactly. That's just about the only valid scenario when you'll need to and should use message contracts.

So, to make a long story short: always use data contracts, practically never use message contracts (unless you absolutely, positively have to).

Marc