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MassTransit–Message Initializers

Let’s have a look at a small example that shows how to publish a message in MassTransit:

What is maybe not immediatelly obvious in the code above, is that when you call publishEndpoint.Publish<OrderSubmitted> a lot of magic is going on.

The generic argument would make you think that the  Publish method expeccts a message of type OrderSubmitted. But we are passing an anonymous object??? And to make it even stranger, we only have the OrderSubmitted interface, we never created a class that implements it???

What is happening? How this even works? The answer to all this magic are Message Initializers.

When calling the Publish method above, you are using a specific overload:

Task Publish<T>(object values, CancellationToken cancellationToken = default) where T : class;

Message initializers make it easy to produce interface messages using anonymous objects. The message initializers will try to match the values of an anonymous object with the properties of the specified interface. While doing that it can use tricks like type conversions, conversion of list elements, matching nested objects, specify header values and even use invariant variables(guaranteeing that the same value is used everywhere inside a message).

Check out the documentation to learn more about what is possible through message initializers: https://masstransit-project.com/usage/producers.html#message-initializers

 

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