Tuesday, September 8, 2020

MassTransit–Create a scoped filter that shares the scope with a consumer

Here is what I wanted to achieve:

I want a MassTransit filter that reads out some user information from a message header and store it in a scoped class. Idea is that the same scope is applicable inside my consumer so that I’m guaranteed that the correct audit information is written into the database.

This use case doesn’t sound too hard and a first look at the documentation showed that you can have scoped filters; https://masstransit-project.com/advanced/middleware/scoped.html#available-context-types

Unfortunately these filters doesn’t share the same scope with the consumer and turn out not to be a good solution for my use case. As I mentioned yesterday I discovered the way to go when having a look at the Masstransit pipeline:

What I need is an implementation of a ConsumerConsumeContext filter(quite a mouthful).

Let’s take a look at the steps involved:

  • First we create a ConsumerConsumeContext filter.
    • Notice that to get it working I had to use the Service Locator pattern and resolve the IoC instance through the context provided in the send method.
  • Now we need to add the necessary registrations. I’m registering the IUserFactory that stores the users data as a scoped instance
    • I’m using Autofac here, but the code is quite similar for other IoC containers
  • As a last step we need to apply the filter to our consumers. I’m doing this through a definition file but there are other ways to configure this as well: