How to serialize Dictionary<string, string> through WCF?

Question

I have a data contract with a data member typed as Dictionary<string, string>.

The generated web service reference exposes this as a member with the type ArrayOfKeyValueOfstringstringKeyValueOfstringstring[].

Has anyone seen this before?

Answer 1

WCF only serializes structure, because what ends up on the wire must be self-contained enough to be useful for any client, not just .NET clients.

Some client developed on a different platform may not share the concept of a 'dictionary', so it would be too constraining to serialize a Dictionary to a representation that carries an implicit knowledge about the underlying class.

The client may not even be object-oriented.

A Dictionary is more than structure - it also contains behavior (e.g. when you assign to a key that already exists, you overwrite that key, etc.) and that behavior cannot travel across the wire.

In other words, Dictionaries and many other .NET types are not interoperable, so WCF will not attempt to preserve them in a ServiceContract.

You would probably be better off designing a custom DataContract for your data.