TypeInitializationException: The type initializer for 'vService.CheckService' threw an exception

Question

I am receiving a FaultException from a WCF service as follows when it is invoked:

2012-04-02 16:26:00.3593|Error|System.ServiceModel.FaultException`1[System.ServiceModel.ExceptionDetail]: The type initializer for 'vService.CheckService' threw an exception. (Fault Detail is equal to An ExceptionDetail, likely created by IncludeExceptionDetailInFaults=true, whose value is:
System.TypeInitializationException: The type initializer for 'vService.CheckService' threw an exception. ----> System.NullReferenceException: Object reference not set to an instance of an object.
   at vService.CheckService..cctor() in d:\working\code\VioletServer\vService\CheckService.cs:line 14
   --- End of inner ExceptionDetail stack trace ---
   at vService.CheckService..ctor()
   at CreatevService.CheckService()
   at System.ServiceModel.Dispatcher.InstanceProvider.GetInstance(InstanceContext instanceContext, Message message)
   at System.ServiceModel.Dispatcher.InstanceBehavior.GetInstance(InstanceContext instanceContext, Message request)
   at System.ServiceModel.InstanceContext.GetServiceInstance(Message message)
   at System.ServiceModel.Dispatcher.InstanceBehavior.EnsureServiceInstance(MessageRpc& rpc)
   at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage41(MessageRpc& rpc)
  ...).

Line 14 of CheckService.cs is

private static string connStr = ConfigurationManager.ConnectionStrings["violetdb"].ConnectionString;

What does the exception mean in this context and how can I resolve it?

---

//CheckService.cs
public class CheckService : ICheckService
{
    private static string connStr = ConfigurationManager.ConnectionStrings["violetdb"].ConnectionString;
    MessageRepository _repo = new MessageRepository(connStr);

    public CheckService(){}

    public CheckService(MessageRepository repo)
    {
        _repo = repo;
    }

    public void SendMessage(string sender, string recipient, string messagetext)
    {
        _repo.DeliverMessage(sender,recipient,messagetext);
    }
}

Answer 1

Most likely your WCF service does not have a connection string named "violetdb" in its application configuration file.

A TypeInitializerException is thrown in this circumstance, because you have a static field which is being initialised ahead of type construction, and because the ConnectionStrings["violetdb"] call is returning null, and it is throwing an NullReferenceException.

Bottom line, check the <connectionStrings> section of your configuration file and ensure that the connection string exists.