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Serializing data using IEnumerable<T> with WebGet

Answer 1

+2 A:

The iterator types generated by the C# compiler are not serializable and never will be.

If you read this page, you'll see that it wouldn't make sense to serialize the iterator.

You need to return an array.

EDIT: The simplest way to do that is to move your iterator to a seperate method, and change WebMethod to

[WebGet]
MyClass[] WebMethod() { return OtherMethod().ToArray(); }

SLaks 2010-01-20 16:28:23

If needed, you can definitely work with `IEnumerable<T>` inside the method...and then use the `IEnumerable<T>.ToArray()` method to return the collection as an Array.

Justin Niessner 2010-01-20 16:31:38

Or you can return a List<T>

Cheeso 2010-01-20 16:37:57

Yes, but why bother?

SLaks 2010-01-20 16:39:15

it depends on how the value is being constructed. Internally a List<T> is an IEnumerable<T>; it's possible the return value is already a List<T>, internally, in which case there is no bother at all.

Cheeso 2010-01-20 16:41:10

@Cheeso: No, it isn't. He's writing an iterator. (See the error message - `X.Y.Z.T+<WebMethod>d__2c` is a generated iterator type)

SLaks 2010-01-20 16:48:10

Thanks guys, I was under the impression that using IEnumerator was 'best practice' I does work for normal data contract serialisation. It only fails for 'WebGet'.I see your point though, and using MyClass[] is definitely not life or death.Thanks!

Jim 2010-01-21 06:29:05

Answer 2

A:

I've run into the same issue, and in my case it's simply not possible to change my entire object graph from iterator-based IEnumerable to concrete types. I simply cannot afford the memory to convert over to concrete types like List or Array. Additionally, what about the case where I return an IEnumerable of some object that has an IEnumerable property. It is unacceptable that I have to recurse my entire object graph converting all IEnumerables.

I don't see any good reason why the DataContractSerializer can't iterate any IEnumerable type and render its elements to XML in the same manner as any other collection type, even if the IEnumerable doesn't have a concrete backing type.

This is a bug which should be fixed.

Jim 2010-04-27 05:36:11

The way that WCF works by default is to use buffered messaging, meaning that the entire serialized object graph of your return value gets built in memory before any of it is sent back to client. Due to this, even if you could return an IEnumerable it wouldn't help with the memory consumption. You can however enable streamed transfers which will cause the message to be sent as it is serialized. Unfortunately, you must use Stream, IXmlSerializable, or Message as your return type to utilize streaming; IEnumerable is still not allowed. See http://msdn.microsoft.com/en-us/library/ms789010.aspx

luksan 2010-06-04 00:36:26

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Serializing data using IEnumerable<T> with WebGet

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