1. What are Migrations ?

Migrations in Rails is a way of describing what the database should look like and synchronize it with the respective model.

Migrations are abstract to the database they are used with. This means that if you have used a MySQL database server when developing the application and the production database server is different let’s say Postgresql the database you defined within the migrations will remain intact and will run just fine on the new database server.

Migrations provide a way to make the database development SVN like… I will cover this latter on so just keep in mind this for now.
 
2. Creating and Running Migrations

A migration is a simple Ruby file in the db/migrate directory.

Each migration file has a name starting with three digits and an underscore. Those digits are the representation of the migrations version (a bit like SVN), because they define the sequence in which the migrations are applied.

To generate a migration type:

ruby script/generate model user

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