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Event Sourcing with Python in 15 Minutes

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Published on Apr 22, 2024 This response is partially generated with the help of AI. It may contain inaccuracies.

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Tutorial: Building an Event Sourced Application in Python

Step 1: Setting Up the Project

  1. Create a new PyCharm project with a virtual environment.
  2. Ensure no additional packages are installed.
  3. Create a test file with a test case and a test method for a dog named Fido.

Step 2: Making the Test Pass

  1. Run the failing test.
  2. Write an add_trick method to append a trick to the dog object.
  3. Verify that the test passes after adding a trick to the dog.

Step 3: Implementing Event Sourcing

  1. Install the Python Event Sourcing library.
  2. Convert the simple Python class to an event-sourced class using the event decorator.
  3. Record events such as registering a dog and adding a trick to the dog.
  4. Collect and store these events to reconstruct the state of the object.

Step 4: Testing the Aggregate

  1. Test the aggregate to ensure the events are correctly stored and reconstructed.

Step 5: Implementing Application Methods

  1. Create an application method, like a dog school, to register a dog (e.g., Fido).
  2. Record the events when registering a dog and adding a trick.
  3. Retrieve the dog details using the repository and return a dictionary with the dog's name and tricks.

Step 6: Adding More Functionality

  1. Test adding tricks to multiple dogs (e.g., Fido and Buster) and ensure the details are saved correctly.
  2. Refactor the code into separate modules for better organization.

Step 7: Implementing Persistence

  1. Change the default persistence module to use the SQLite module for persistent storage.
  2. Specify the database name to store the events persistently.
  3. Verify that the events are saved in the database and can be retrieved even after restarting the application.

By following these steps, you can successfully build an event-sourced application in Python, leveraging the concepts of event sourcing for efficient data management and state reconstruction.

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