How to write a WCF service with in-memory persistent storage?

Question

I wrote a WCF service, but the data stored in the Service implementation doesn't persists between calls, not even if stored in a static variable. What can I do?

The service implementation is as follows:

public class Storage : IStorage
{
    protected static object[] _data;

    #region IStorage Members

    public void Insert(object[] data)
    {
        lock (_data)
        {
             _data = _data.Concat(data).ToArray();
        }
    }

    public object[] SelectAll()
    {
        lock (_data)
        {
            return (object[])_data.Clone();
        }
    }

    #endregion
}

The service host is a console application:

static void Main(string[] args)
{
    ServiceHost serviceHost =
       new ServiceHost(typeof(TimeSpanStorage));
    serviceHost.Open();
    Console.WriteLine("Service running.  Please 'Enter' to exit...");
    Console.ReadLine();
}

Answer 1

By default WCF instanceMode is set to Per call, meaning data used in the service is specific to that client for that method call.

On your implementation try adding

[ServiceBehavior(InstanceContextMode=InstanceContextMode.Single, ConcurrencyMode=ConcurrencyMode.Single)]
public class MyService: IService

This makes the service essentially a singleton.