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  • Active Record Migrations In Rails

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    Migrations in Rails

    Active records provide us with a very useful feature to change or alter our database schema in ruby on rails.

    Through these migrations we can make necessary changes to our database and make changes in our tables and rows.

    Active records detects the changes we have made and automatically update the database.

    The command to tell active records to update the changes in the schema is 

    rake db:migrate

     Migrations which we can use to alter our schema are as fallows :

    • Creating a table

    To create a table we will have to write this command in console

    $ rails generate model user name:string email:string

    and then run

    $ rake db:migrate

    Now, the migration file will look like this

    class ChangeUsers < ActiveRecord::Migration
      def change
        create_table :users do |t|
          t.string :name
          t.string :email
     
          t.timestamps null: false
        end
      end
    end
    • Adding a column to an existing table

    To add a column to an existing table we need to write this command in console

    $ rails generate migration add_column_address_to_users address:text

    and then run

    $ rake db:migrate

    Now, the migration file will look like this

    class AddColumnAddressToUser < ActiveRecord::Migration
      def change
        add_column :users, :address, :text
      end
    end

    With this, an address column with data type text will be added to the user table.

    • Adding an index to the added column

    To add an index to the added column we need to write this command in console

    $ rails generate migration add_column_address_to_users address:text:index

    and then run

    $ rake db:migrate

    Now, the migration file will look like this

    class AddColumnAddressToUser < ActiveRecord::Migration
      def change
        add_column :users, :address, :text
        add_index :users, :address
      end
    end
    • Removing a column from table

    To remove a column from an existing table we need to write this command in console

    $ rails generate migration remove_column_address_from_users address:text

    and then run

    $ rake db:migrate

    Now, the migration file will look like this

    class AddColumnAddressToUser < ActiveRecord::Migration
      def change
        remove_column :users, :address, :text
      end
    end
    • Adding a reference

    To add a reference to a table of some another table we need to write this command in console

    $ rails generate migration add_refrence_user_to_guests

    and then run

    $ rake db:migrate

    Now, the migration file will look like this

    class AddUserRefToGuests < ActiveRecord::Migration
      def change
        add_reference :guests, :user, index: true
      end
    end

    In this the user table is added as a reference to the guests table.

    This migration will create a user_id column and appropriate index in the guests table.

    So these were some of the important migrations of active records which are used frequently while creating we b based applications.

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