Explaination about migrate command in django

Question

Can anyone explain me, how migration will happened in django? Actually I want full backend procedure of "./manage.py migrate" command

Answer 1

It was explained once at the "django under the hood" conference by the author. I have a summary of that: http://reinout.vanrees.org/weblog/2014/11/14/2migrations.html

The way it works is by chopping all operations into tiny dependencies. Every individual field that has to be created is turned into a tiny dependency step. After the list of steps is sorted (via the dependency-resolving loop) into the correct list of steps, an optimiser goes through the list and optimises it. If a model gets created and deleted, nothing needs to be done, for instance.

The final part of the puzzle is the graph. It builds a directed graph of all basic migrations in memory. It needs to read all the models on disk for that. It also looks in the database. There’s a table in there that marks which migrations (or rather: nodes in the migration graph) have been applied.

If you want to look at the code, here are some pointers:

• django/db/migrations/autodetector.py, start at _detect_changes()
• django/db/migrations/optimizer.py, start at reduce()
• django/db/migrations/graph.py
• django/db/migrations/loader.py