Migrations Methods

Learn about the various methods in Rails migrations and how to use them.

Writing your own migrations

The generate command only provides you with a template to work off of. It will create a single table with the specified attributes, and a migration will be generated for the command. To really make use of migrations, you need to be familiar with the various methods it contains.

Note: A migration file is created when the command is run for the first time. Trying to use the generate model command with the same model name will give an error. You will have to run migration commands to make changes to the model.

Up and down methods

The up and down methods perform opposing functions. Whatever transformation is made by your up method should be exactly reverted when you run the down method. Essentially, running the up and down methods in succession should leave the database schema unchanged.

If your up method creates a table, your down method should drop it. It is recommended that the reversal of the transformations using the down method be done in reverse order.

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