# 
##  

Migrations are a convenient and easy way to make consistent changes to our database structure over time.
This methodology is compatible with the Agile and XP methods used by [Rails](https://www.educative.io/answers/what-is-ruby-on-rails) developers worldwide.
 
Migration is the subclass of `ActiveRecord::Migration`, which overrides the two needed methods:

* `self.up` 
* `self.down` 

# 
## Structure of rails `ActiveRecord` migrations

```
class SampleMigration < ActiveRecord::Migration
        def self.up
        end

        def self.down
        end
end
```

 We can perform the following operations in `self.up` and `self.down` methods:

* Create tables and indexes
* Add data
* Manipulate models and so on


In both practice and theory, the concept is straightforward: 
* The `self.up` method definition contains the actions we wish to migrate to the next version of the schema. 
* Put anything we need to do to undo the change in the `self.down` method.



# 
## Code example
Let's look at the code below:

class SampleMigration < ActiveRecord::Migration
     def self.up
          create_table :people do |t|
            t.column :name, :string
       end
     end

     def self.down
       drop_table :people
     end
end

## Code explanation

* Line 1: We created the `SampleMigration` subclass from the `ActiveRecord::Migration`.
* Line 2: We implement the `self.up` method.
* Lines 3 to 4: We use `SampleMigration` to create a table `people` with a string column named `name`.
* Lines 8: We implement the `self.down` method.
* Lines 9: We use `SampleMigration` to drop the `people` table.



rortar.tar.gz

How to use ActiveRecord migrations in Rails 6

Migrations enable consistent database changes over time, essential for Agile development. Implement `self.up` for forward migrations and `self.down` for reversals.

How to use ActiveRecord migrations in Rails 6

Structure of rails ActiveRecord migrations

Code example

Code explanation

Structure of rails `ActiveRecord` migrations