Agile Web Development with Rails 5, 1st Edition

Iteration E1: Creating a Smarter Cart

Associating a count with each product in our cart is going to require us to modify the line_items table. We’ve used migrations before; for example, we used a migration in ​Applying the Migration​ to update the schema of the database. While that was as part of creating the initial scaffolding for a model, the basic approach is the same:

depot> bin/rails generate migration add_quantity_to_line_items quantity:integer

Rails can tell from the name of the migration that you’re adding columns to the line_items table and can pick up the names and data types for each column from the last argument. The two patterns that Rails matches on are add_XXX_to_TABLE and remove_XXX_from_TABLE, where ...