>From the Django docs, for any ORM query made, the DB alias to use is determined by the following rules:
- Checks if the using keyword is used either as a parameter in the function call or chained with QuerySet. - Consults the DB routers in order until a match is found. - Falls back to the default router which always returns default as the alias. Using the router scheme works perfectly for ORM queries. However, when it comes to using transaction APIs (like the transaction.atomic construct), it becomes mandatory to specify the *using* kwarg explicitly in all of its publicly exposed APIs if a DB other than the default alias has to be chosen. To illustrate why this is a problem, consider the following scenario: - A DB router exists such that it directs queries to a specific database based on a value set in *thread-local* storage by a middleware. - When ORM queries from within the view are fired, they automatically get forwarded to the right DB *without explicitly citing* the using keyword owing to the router. - But if the transaction.atomic construct is used, the using keyword would have to be explicitly specified each time. While this might seem fine, it creates the following problems: 1. For large code bases, it becomes highly unwieldy to make sure that the *using* keyword has been mentioned in every transaction API call. Also, if one tries to implement the above scheme in an already existing code base, it would be impractical to add the using keyword in all lines calling the transaction APIs. 2. It doesn't gel well with the the routers framework. A proposed workaround could to be to add a separate method named *db_for_transaction* to the routers framework which would be consulted by the transaction APIs first, before falling back to using the default DB alias. 1. Having a separate method for transaction is good because it need not be mangled up with the other methods i.e db_for_read / db_for_write as they clearly indicate certain operational semantics which aren't tied to a transaction since it can have both reads and writes within it. 2. Also, if in the future, there is some special info that can be delivered to the transaction based on which a decision regd which DB to use could be made, then it would be cleanly isolated into its own method. If we can finalise on this, I could submit a PR for the same. -- You received this message because you are subscribed to the Google Groups "Django developers (Contributions to Django itself)" group. To unsubscribe from this group and stop receiving emails from it, send an email to django-developers+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/django-developers/b62206d5-b001-413c-a58e-e78c08596497n%40googlegroups.com.