When generating migrations via the command line you can specify the type of field you want to create. In the case of decimals this would give
rails generate migration AddAmountToOrder amount:decimal
This way you get a migration with a decimal column for your database. But you have to manually go to the file and add values for precision and scale like this
t.decimal :amount # generated, but...
t.decimal :amount, precision: 10, scale: 2 # ... wanted!
How can you supply these values via the command line so that you can immediately do a rake db:migrate
without first adding precision and scale to the migration file?