When we create a web application we generally create models which are referred to as tables in the database. Sometimes we need to add a column to the existing table or remove an unused column from the table or just change the column. The way to do all this through migrations are -:
Adding a Column
Suppose we have a user table and we need to add a column "last_name" to it .
$ rails generate migration add_column_last_name_to_user last_name:string
$ rails generate migration add_column_last_name_to_user last_name:string
After writing this run the migration command.
$ rake db:migrate
$ rake db:migrate
The migration file generated will be like :
class AddColumnLastNameToUser < ActiveRecord::Migration def change add_column :users, :last_name, :string endend
class AddColumnLastNameToUser < ActiveRecord::Migration
def change
add_column :users, :last_name, :string
end
end
Changing a Column
If we want to change the datatype of last_name to text , so we need to write the following in our migration file :
class ChangeColumnLastNameInUser < ActiveRecord::Migration def change change_column :users, :last_name, :text endend
class ChangeColumnLastNameInUser < ActiveRecord::Migration
def change
change_column :users, :last_name, :text
end
end
After this run the migration command.
$ rake db:migrate
$ rake db:migrate
Removing a Column
If we want to remove the last_name column from our user table then we write:
$ rails generate migration remove_column_last_name_from_user last_name:text
$ rails generate migration remove_column_last_name_from_user last_name:text
After this run the migration command.
$ rake db:migrate
$ rake db:migrate
Our migration file will be like :
class RemoveColumnLastNameFromUser < ActiveRecord::Migration def change remove_column :users, :last_name, :text endend
class RemoveColumnLastNameFromUser < ActiveRecord::Migration
def change
remove_column :users, :last_name, :text
end
end
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