Question

When I read Rails book, each time they create a new database, always follow a db:migrate.

rails generate scaffold school
rake db:migrate

In console view, I see at first line, Rails create some files, no problem. but in second line, I see that Rails isn’t really change anything. I have view some files that Rails nearly create and see no change too.

So, what the purpose of line 2, please tell me.

Thanks 🙂

Answer 1

The rake migrates the changes into your database. It is which acttually changes the database schema to match your previously generated scaffolded model.

Without it, you wouldn’t have a table to write your objects into. Or in case of changed model, the table could differ from your model, leading to error.

When you generate a model (or scaffold one) a migration file is created in your db/migration directory. It is a pure text file, you can create such manually, if you want. This is the tool for the iterative development in rails regarding the database. Each migration adds some change to the system. When you run rake db:migrate your database is updated by the given migrations. This is a handy tool in case of distributed development, when one programmer can check out the code from the repository, and can run the migrations on his own development database.