Versioning and History

[geraldnyeo]

This PR implements the backend support for the "Versioning and History feature". It adds a "versions" table which tracks history for entries in the "answers" table, and implements the required version schema, controller, and routes.

This change is non-breaking and should be merged before source-academy/frontend#3659.

Database Changes

This PR adds a "versions" table with the following columns:

• id
• name
• version: the content of the answer is stored here
• answer_id
• restored
• restored_from
• inserted_at
• updated_at

Each entry in the table represents a version of an answer (from the answer table). There can be multiple versions for one answer.

The migration for this table has been added here: \priv\repo\migrations\20260219073155_create_versions.exs. To update the database to the latest version, run:

mix ecto.migrate

Database Design Decisions
Currently, each answer is indexed by a unique submission id + question id combination, which most methods and routes use. Multiple versions of the same answer would have the same submission id + question id combination, and storing them in the current answers table would introduce a lot of breaking changes, so we decided to store them in a separate versions table.

We also decided to store both the answer content in both the answer and versions table. Each version entry references an entry in the answers table (which cannot be null). Replacing the "answer" field in the answers table with some reference to the versions table (which also cannot be null) makes it difficult to create new answers, and requires an extra join every time an answer is searched for.

Routes

• GET /v2/courses/:course_id/assessments/question/:questionid/version/history
• POST /v2/courses/:course_id/assessments/question/:questionid/version/save
• PUT /v2/courses/:course_id/assessments/question/:questionid/version/:versionid/name

Additional Notes

• The schema.png in the README has not been updated to reflect these changes.

Related Issues / PRs

• Versioning and history for student submissions frontend#3074
• Versioning and history frontend#3659

[RichDom2185]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces backend support for versioning and history of answers, which is a significant feature. The implementation adds a new versions table, along with the necessary schema, controller, and routes. The changes are generally well-structured, but there are several critical issues related to error handling and control flow that could lead to crashes. Specifically, several functions don't handle potential {:error, ...} tuples from find_team, leading to MatchError exceptions. There are also opportunities to reduce code duplication and improve adherence to Elixir conventions. I've provided specific comments and suggestions to address these points.

[coveralls]

coverage: 88.577% (-0.3%) from 88.926% — geraldnyeo:versions-feature into source-academy:master