CODEWITHSUNDEEP
c#.netwcftask-parallel-libraryasync-await
bobbyalex
bobbyalex

Reputation: 2751

Returning an item in a WCF method that uses await

I am creating a RESTful web service using WCF. Consider the Service contract and implementation below:

[ServiceContract]
    public interface IItemsSaleService
    {
        [OperationContract]
        [WebInvoke(Method = "GET", ResponseFormat = WebMessageFormat.Json, BodyStyle = WebMessageBodyStyle.Wrapped, UriTemplate = "getItemDetails/{itemId}")]
        SaleItem GetItemDetails(string itemId); //GET
}

//IMPLEMENTATION

async public SaleItem GetItemDetails(string itemId) //This wont work. It should be Task<SaleItem>
        {

            SaleItem item = await FindItem(itemId);
            return item;
        }

Assume that the FindItem is a thirdparty API method. Since I am using await, the method GetItemDetails has to be marked async and hence cannot return SaleItem. It has to return void or a Task which wont work for me as the method HAS to return SaleItem for the serializer to convert it to JSON and return it back to the client.

How do I fix this?

Another related question:

Method A calls Method B calls Method C - Method C uses await. Does this automatically require all the other methods to be async and hence always return Task<> or void?

Upvotes: 4

Views: 1391

Answers (1)

Yuval Itzchakov
Yuval Itzchakov

Reputation: 149578

Assume that the FindItem is a thirdparty API method. Since I am using await, the method GetItemDetails has to be marked async and hence cannot return SaleItem. It has to return void or a Task which wont work for me as the method HAS to return SaleItem for the serializer to convert it to JSON and return it back to the client.

It WILL work. From MSDN:

Clients can offer the developer any programming model they choose, so long as the underlying message exchange pattern is observed. So, too, can services implement operations in any manner, so long as the specified message pattern is observed.

This means that WCF can switch between synchronous and asynchronous patterns for a single message. An extensive answer is provided in Noseratios link: Different forms of the WCF service contract interface

Method A calls Method B calls Method C - Method C uses await. Does this automatically require all the other methods to be async and hence always return Task<> or void?

Async methods by nature propogate all the way up. A method which uses the await keyword will have to mark its method async and have a return type of either Task, Task<T>, or void. Notice a void returning async method is ment solely for the compatability of async event handlers, and shouldn't be used outside of that scope.

There are cases when making your method async isn't necassery, and simply returning the inner called Task will suffice, you can read more about it here: Any difference between "await Task.Run(); return;" and "return Task.Run()"?

Upvotes: 4

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