Why does schema.rb change (in the eyes of Git) when just running rake db:migrate?

Question

This is a little general I know, but it's been bugging the hell out of me. I've been working on lots of rails projects remotely with Git and every time I do a git pull and see that there is some sort of data change (migration, or schema.rb change) I do a rake db:migrate.

These generally run fine and I can continue working. But if you do a git pull and then git status, your working directory is clean (obviously) then do a rake db:migrate (obviously when there are changes) and another git status and all the sudden your db/schema.rb has changed. I have been just doing a git checkout immediately to reset back to the latest committed version of the schema.rb file, but why should this be necessary?! What is rails doing? Updating a timestamp? I can't seem to figure out what the diff is but maybe I'm just missing something?

Answer 1

The schema enables machines to run rake db:schema:load when being setup for the first time instead of having to run the migrations, which can go out of date if models are renamed or removed, etc. It's supposed to update after a migration, and you always want to latest version checked into source control.

Answer 2

schema.rb reflects your database schema so when you migrate(with changes) it follow that your schema also changes to reflect your db change. I usually add schema.rb to our gitignore, along with database.yml (probably because instead of using schema:load like the one below, i usually do a sql dump when cloning an existing app - but that's just me)

Answer 3

The order of attributes in the dump reflects the order of the attributes in the database, and that can get out of sync if one person has been playing around locally with migrations, running them forwards and backwards manually, and editing things to get them just so. It's possible to create a state where the attribute order in the pusher's schema.rb is different from what everyone else will see when they run the migrations.

If it's easy to recreate your development data, just rebuild the database from schema.rb - then everyone is back in sync (but remember you can't reload the data from a SQL dump that also creates the table - that will recreate the problem. it has to be a data-only dump/load). In the worst case, you can create a migration to delete the column and another to re-add it.