Conventions can be used to identify which types are messages, commands, and events, instead of using marker interfaces. This can be done to avoid references to the NServiceBus assembly, referred to as unobtrusive mode. This is ideal for use in cross-platform environments.
Currently conventions exist to identify:
Message types can be defined in a Portable Class Library (PCL) and shared across multiple platforms, even if the platform does not use NServiceBus for message processing.
var conventions = endpointConfiguration.Conventions();
conventions.DefiningCommandsAs(type => type.Namespace == "MyNamespace.Messages.Commands");
conventions.DefiningEventsAs(type => type.Namespace == "MyNamespace.Messages.Events");
conventions.DefiningMessagesAs(type => type.Namespace == "MyNamespace.Messages");
conventions.DefiningDataBusPropertiesAs(property => property.Name.EndsWith("DataBus"));
conventions.DefiningTimeToBeReceivedAs(type => type.Name.EndsWith("Expires") ? TimeSpan.FromSeconds(30) : TimeSpan.MaxValue);
In .NET, the namespace is optional and can be null. If any conventions do partial string checks, for example using EndsWith or StartsWith, then a null check should be used. Include . at the start of the convention to avoid a null reference exception during type scanning.
Using both default and custom conventions
Defining a custom convention will overwrite the default convention. If both default and custom conventions are needed, the default conventions must be specified along with the custom conventions.
var conventions = endpointConfiguration.Conventions();
conventions.DefiningCommandsAs(type =>
type.Namespace == "MyNamespace.Messages.Commands"
|| typeof(ICommand).IsAssignableFrom(type)
);
conventions.DefiningEventsAs(type =>
type.Namespace == "MyNamespace.Messages.Events"
|| typeof(IEvent).IsAssignableFrom(type)
);
conventions.DefiningMessagesAs(type =>
type.Namespace == "MyNamespace.Messages"
|| typeof(IMessage).IsAssignableFrom(type)
);
conventions.DefiningDataBusPropertiesAs(property =>
property.Name.EndsWith("DataBus")
|| typeof(IDataBusProperty).IsAssignableFrom(property.PropertyType) && typeof(IDataBusProperty) != property.PropertyType
);
conventions.DefiningTimeToBeReceivedAs(type =>
type.Name.EndsWith("Expires")
? TimeSpan.FromSeconds(30)
: type.GetCustomAttribute<TimeToBeReceivedAttribute>(false)?.TimeToBeReceived ?? TimeSpan.MaxValue
);
Encapsulated conventions
Messaging conventions can be encapsulated into a class.
class MyNamespaceMessageConvention : IMessageConvention
{
public bool IsMessageType(Type type) => type.Namespace == "MyNamespace.Messages";
public bool IsCommandType(Type type) => type.Namespace == "MyNamespace.Messages.Events";
public bool IsEventType(Type type) => type.Namespace == "MyNamespace.Messages.Commands";
public string Name { get; } = "MyNamespace message convention";
}
These conventions can be added to the endpoint.
endpointConfiguration.Conventions().Add(new MyNamespaceMessageConvention());
Multiple encapsulated conventions can be applied to the same endpoint. A class will be a considered a message, command, or event if any convention matches it.
Adding an instance of IMessageConvention does not override the default conventions.
Attributes
If attributes are preferred over marker interfaces then this can be achieved using NServiceBus.AttributeConventions, a community package that allows using attributes instead of interfaces.