MigrationRails Generate Migration (rails g migration) is the generator for an ActiveRecord migration. Migrations define mutations to your database schema, including adding and removing database tables, columns and indexes.
The Rails migration generator will do it's best to infer the contents of your migration from the migration name you pass, and the fields.
For example, if your run the following generator —
rails g migration AddNameToUser name:string:indexRails will automatically generate the following migration —
class AddNameToUser < ActiveRecord::Migration[7.0]
def change
add_column :users, :name, :string
add_index :users, :name
end
endThere's too much information on Rails Migrations to cover it all here. If you'd like more information though, I've written a Rails Generate Migration Reference Guide that you might find handy.
For your reference, ActiveRecord migrations (and hence all model-based generators) support the following data types —
:primary_key # A unique key that identifies a model record.
:string # Short text such as titles.
:text # Long text data such as documents of information.
:integer # For storing whole numbers.
:float # For storing floating-point numbers.
:decimal # For storing decimal numbers.
:datetime # Stores both date and time.
:timestamp # Stores both date and time.
:time # Stores only the time.
:date # Stores only the date.
:binary # For storing binary data blobs like images.
:boolean # True or false values. rails g migrationrails g migration Migration Name
Migration Field(s)
Generator Options
Runtime Options
❯ rails g migration
Usage:
rails generate migration NAME [field[:type][:index] field[:type][:index]] [options]
Options:
[--skip-namespace], [--no-skip-namespace] # Skip namespace (affects only isolated engines)
[--skip-collision-check], [--no-skip-collision-check] # Skip collision check
-o, --orm=NAME # ORM to be invoked
# Default: active_record
ActiveRecord options:
[--timestamps], [--no-timestamps] # Indicates when to generate timestamps
# Default: true
[--primary-key-type=PRIMARY_KEY_TYPE] # The type for primary key
--db, [--database=DATABASE] # The database for your migration.
# (By default, the current environment's primary database is used.)
Runtime options:
-f, [--force] # Overwrite files that already exist
-p, [--pretend], [--no-pretend] # Run but do not make any changes
-q, [--quiet], [--no-quiet] # Suppress status output
-s, [--skip], [--no-skip] # Skip files that already exist
Description:
Generates a new database migration. Pass the migration name, either
CamelCased or under_scored, and an optional list of attribute pairs as arguments.
A migration class is generated in db/migrate prefixed by a timestamp of the current date and time.
You can name your migration in either of these formats to generate add/remove
column lines from supplied attributes: AddColumnsToTable or RemoveColumnsFromTable
Example:
`bin/rails generate migration AddSslFlag`
If the current date is May 14, 2008 and the current time 09:09:12, this creates the AddSslFlag migration
db/migrate/20080514090912_add_ssl_flag.rb
`bin/rails generate migration AddTitleBodyToPost title:string body:text published:boolean`
This will create the AddTitleBodyToPost in db/migrate/20080514090912_add_title_body_to_post.rb,
with this in the Change migration:
add_column :posts, :title, :string
add_column :posts, :body, :text
add_column :posts, :published, :boolean
Migration names containing JoinTable will generate join tables for use with
has_and_belongs_to_many associations.
Example:
`bin/rails g migration CreateMediaJoinTable artists musics:uniq`
will create the migration
create_join_table :artists, :musics do |t|
# t.index [:artist_id, :music_id]
t.index [:music_id, :artist_id], unique: true
end