I'd like to automatically open a PostgreSQL transaction and inject inside Context. If an operation is query the transaction can be read-only, which is a good thing to declare in advance. mutation operations can be opened with the user_id being logged. Transactions should be automatically closed: COMMIT on success and ROLLBACK when a failure has occurred. Such a strategy could be implemented with an axum middleware for example.

There is no way to implement such behavior with extensions.

• request(&self, ctx: &ExtensionContext<'_>, next: NextRequest<'_>)
  • can't understand which kind of transaction to open (read-only/mutable)
  • has no means of injecting transactions into the context
  • has access to the Response to figure out whether the operation has failed (commit/rollback)
• pre_request(&self, ctx: &ExtensionContext<'_>, mut request: Request, next: NextPrepareRequest<'_>)
  • knows which kind of transaction to open (read-only/mutable)
  • can inject the transaction into request.data, thus the context
  • can't close the transaction as it doesn't know the result of the operation (success/failure)

As can be seen in #1707 — &self and extension contexts are immutable. They are just views over the schema/session/query contexts.