This makes perfect sense as the primary purpose of the DataContractJsonSerializer is to be used with WCF, and just as its name suggests, it’s a JSON serializer for DataContract types.
One interesting side effect of the above is that you can’t use DataContractJsonSerializer with anonymous types.
Unfortunately you won’t be able to deserialize the JSON string back into an anonymous type as all the available deserialize methods requires a type which has a parameterless constructor.
Another main functional difference between these two serializers is how they deal with dictionaries.
Take this simple dictionary for instance:
The DataContractJsonSerializer serializes dictionaries as an array of KeyValuePair objects:
This subtle different might seem trivial at first, but it can make a huge difference when you’re dealing with data that are originated from a non-.Net language. A perfect example came couple of days ago when we were testing out the Facebook graph API and one of the JSON responses we came across was a dictionary whose keys were numeric IDs like this:
In cases like this, you simply won’t be able to deserialize this JSON using the DataContractJsonSerializer!