What is bin/rake DB:Migrate ?

Like Andrew mentioned, rake db:migrate generates a migration file. In the file, Rails creates a class that inherits from ActiveRecord:: Migration. In other words, this is Rails way of telling the database what to do. The class will have generated methods specified by what you command. For example, if you want to drop a specific table in the database, Rails will automatically create the class and methods needed to drop that table in the database.

If you check inside your rails app directory db/migrate, you will see you the generated files named with a prefix of what looks like random numbers and along with your command. (ex. 20141019001737_create_tests.rb). These numbers represent a timestamp. The database saves the latest timestamp to a table. So when you create a migration, it runs all of the previous migrations associated with the latest timestamp, then updates the database table with your newly generated timestamp.

Hope that helps!

I think when you run 'generate', that creates a migration file. When you run migrate it actually CREATES the new section in your database, using that migration file.