Question

I would like to supplement the endpoints which I subscribe too in my UnicastBusConfig section of my App.config file to add in another queue to subscribe to.

To do this ive added a custom configuration source as follows

public class MyConfigSource : IConfigurationSource
{
    public T GetConfiguration<T>() where T : class, new()
    {
        // the part you are overriding
        if (typeof(T) == typeof(UnicastBusConfig))
        {
            var config = ConfigurationManager.GetSection(typeof(T).Name) as UnicastBusConfig;

            config.MessageEndpointMappings.Add(new MessageEndpointMapping() { Endpoint = "MyQueue", Messages = "MyMessageNamespace" });
        }

        // leaving the rest of the configuration as is:
        return ConfigurationManager.GetSection(typeof(T).Name) as T;
    }
}

however I get an exception when I call Add on the existing MessageEndpointMappings collection:

Exception when starting endpoint, error has been logged. Reason: The
configuration is read only.

Is there a better way to load an existing configuration and add bits to it in code?

Answer 1

Yes unfortunately the mappings collection is set as readonly!

Here is a workaround (sorry about the usage of reflection!) (and I’m also using the new way to override configuration settings IProvideConfiguration<T>):

class UnicastBusConfigOverride : IProvideConfiguration<UnicastBusConfig>
{
    public UnicastBusConfig GetConfiguration()
    {
        var unicastBusConfig = Configure.ConfigurationSource.GetConfiguration<UnicastBusConfig>();

        typeof(ConfigurationElementCollection)
            .GetField("bReadOnly", BindingFlags.Instance | BindingFlags.NonPublic)
            .SetValue(unicastBusConfig.MessageEndpointMappings, false);

        unicastBusConfig.MessageEndpointMappings.Add(new MessageEndpointMapping() { Endpoint = "MyQueue", Messages = "MyMessages" });

        return unicastBusConfig;
    }
}

BTW, I’ll make sure we fix this for the next major release of NServiceBus, see https://github.com/NServiceBus/NServiceBus/issues/952