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Discover the intricacies of `Django Database Routing` and learn how to effectively migrate multiple databases without hassle.
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This video is based on the question https://stackoverflow.com/q/67514890/ asked by the user 'Aagam Sheth' ( https://stackoverflow.com/u/13961650/ ) and on the answer https://stackoverflow.com/a/67515964/ provided by the user 'Abdul Aziz Barkat' ( https://stackoverflow.com/u/14991864/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding Django Database Routing: A Complete Solution to Migrate Multiple Databases

Django is a powerful web framework that allows developers to build web applications quickly and efficiently. One of its impressive features is the support for multiple databases, which makes it possible to route database operations to different sources. However, managing database migrations across several databases can become quite tricky, particularly when routing isn't set up correctly. Today, we are going to tackle a common problem faced by Django developers — migrating multiple databases effectively using Django's built-in routing system.

The Problem

Imagine you have a Django project with three databases configured in your settings.py, and you've established routers for two applications. You want to run migrations specifically for each app's database. However, upon attempting a migration, Django only processes the default database alongside one other specified database. Changing the order of databases only resolves to migrating either the first or the second but never both. This scenario can become increasingly problematic, especially as your project expands to include more databases.

Your Configuration

You have defined the databases and the relevant routers in your settings.py, but the expected behavior is not happening:

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For instance, executing commands like:

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always leads to only one database being migrated, making the process cumbersome as your project evolves.

The Solution: Updating the Router Logic

The root cause of this issue lies within the implementation of your database routers. The allow_migrate method in your routers should not only check if a certain app label is present but also accommodate other routers that may need to make decisions.

Revising the CredRouter

The update for your CredRouter.py involves returning None for migrations that are not relevant to the cred_db, thereby allowing other routers the opportunity to decide on migrations meant for their databases:

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Updating the DMSRouter

You can apply similar correction for your DMSRouter.py. Ensure it also follows the same logic:

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Conclusion

With the updated logic in your routers, running migrations should now appropriately and seamlessly direct to the specified databases without skipping or incorrectly ordering tasks. This adjustment will not only help in resolving the current issue but also scales well as your project evolves to manage multiple databases effectively.

You can now manage your database migrations more efficiently without the need for manually reordering databases, paving the way for smoother future developments. Enjoy coding away with Django!