Resolves ENGA-923 "Modify django-bigquery-exporter base to include decorator for custom_field"

[DevDaveFrame]

ENGA-923

Non-technical Context

Replacing the custom_fields array with a single fields array and a decorator to identify custom methods allows for a cleaner implementation and higher visibility for custom fields

Technical Context

The current decorator implementation is very bare bones. It just adds a custom attribute, "is_custom_field" to the function or method. This allows the _process_queryset method to check for the presence of the field, and determine whether to check the model or call the method.

The decorator isn't strictly necessary in this implementation but it does reduce the risk of accidental naming collisions with existing model fields and it opens up the possibility of additional transformations or validation in the future. And it makes it easier to see what methods are custom fields at a glance.

While writing tests for the new decorator, I also refactored the existing tests to DRY up the test class by using a fixture rather than rewriting the test exporter class every time.

Developer

• Ensure code complies with the style guide
• Devise edge cases to test the bug fix or feature being merged
• Make sure the code is clean and understandable
• Ensure code is not overly inefficient
• Code changes include a migration
  • Migration modifies large table and has been run against full db to estimate completion time
  • Migration modifies a small table and has only been run against slim db
  • There are no conflicting migration leaf nodes
• Ensure documentation is understandable and accurate, including:
  • Code comments and doc strings
  • Technical documentation

Reviewer

• Ensure code complies with the style guide
  • If there are few or minor issues, add inline comments
  • If there are many issues or it seems like the developer did not follow the style guide, leave a comment asking them to do so
• Devise edge cases to test the bug fix or feature being merged
• Make sure the code is clean and understandable
  • Ask for inline comments on unclear sections
• Ensure code is not overly inefficient
• Ensure documentation is understandable and accurate, including:
  • Code comments and doc strings
  • Technical documentation
• There are no conflicting migration leaf nodes

[echan217]

LGTM! Nice refactor!