Question

I have a sequence of migrations in a rails app which includes the following steps:

1. Create basic version of the ‘user’ model
2. Create an instance of this model – there needs to be at least one initial user in my system so that you can log in and start using it
3. Update the ‘user’ model to add a new field / column.

Now I’m using ‘validates_inclusion_of’ on this new field/column. This worked fine on my initial development machine, which already had a database with these migrations applied. However, if I go to a fresh machine and run all the migrations, step 2 fails, because validates_inclusion_of fails, because the field from migration 3 hasn’t been added to the model class yet.

As a workaround, I can comment out the ‘validates_…’ line, run the migrations, and uncomment it, but that’s not nice.

Better would be to re-order my migrations so the user creation (step 2) comes last, after all columns have been added.

I’m a rails newbie though, so I thought I’d ask what the preferred way to handle this situation is 🙂

Answer 1

The easiest way to avoid this issue is to use rake db:schema:load on the second machine, instead of db:migrate. rake db:schema:load uses schema.rb to load the most current version of your schema, as opposed to migrating it up form scratch.

If you run into this issue when deploying to a production machine (where preserving data is important), you’ll probably have to consolidate your migrations into a single file without conflicts.