Rails Migrations
Shameless copy of http://garrettsnider.backpackit.com/pub/367902
Make sure you view the (short) screencast by DHH
Valid as of Rails 1.1.2
VERIFY: To enable full use of ruby schema support, uncomment ‘config.active_record.schema_format = :ruby’ in your /config/environment. (Update: The rails schema mechanism is the default as of Rails 1.1)
rake db:schema:dump: run after you create a model to capture the schema.rb
rake db:schema:import: import the schema file into the current database (on error, check if your schema.rb has ”:force => true” on the create table statements
./script/generate migration MigrationName: generate a new migration with a new ‘highest’ version (run ’./script/generate migration’ for this info at your fingertips)
rake db:migrate: migrate your current database to the most recent version
rake db:migrate VERSION=5: migrate your current database to a specific version (in this case, version 5)
(run rake -T for most of this information as rake usage information)
Example schema.rb:
ActiveRecord::Schema.define(:version => 2) do
create_table "comments", :force => true do |t|
t.column "body", :text
t.column "post_id", :integer
end
create_table "posts", :force => true do |t|
t.column "title", :string
t.column "body", :text
t.column "created_at", :datetime
t.column "author_name", :string
t.column "comments_count", :integer, :default => 0
end
end
create_table(name, options)
drop_table(name)
rename_table(old_name, new_name)
add_column(table_name, column_name, type, options)
rename_column(table_name, column_name, new_column_name)
change_column(table_name, column_name, type, options)
remove_column(table_name, column_name)
add_index(table_name, column_name, index_type)
remove_index(table_name, column_name)
See the Rails API for details on these.
Example migration:
class UpdateUsersAndCreateProducts < ActiveRecord::Migration
def self.up
rename_column "users", "password", "hashed_password"
remove_column "users", "email"
create_table "products", :force => true do |t|
t.column "name", :text
t.column "description", :text
end
end
def self.down
rename_column "users", "hashed_password", "password"
add_column "users", "email"
drop_table "products"
end
end
Tip: if you need to manually override the the schema version that in the DB:
ruby script/runner 'ActiveRecord::Base.connection.execute(
"INSERT INTO schema_info (version) VALUES(0)")'
Thanks to the Chad Fowler’s new Rails Recipes book for this one. Note that (duh) you can run any sql like this.
On OS X, I’m using TextMate with the syncPEOPLE on Rails v.0.9
TextMate Bundle. This provides the following…
(snipped from the release notes)
Snippets are small capsules of code that are activated by a key sequence followed by the [tab] key. For example, mcdt[tab] will activate the Migration Create and Drop Table snippet.
mcdt: Migration Create and Drop Table
mcc: Migration Create Column
marc: Migration Add and Remove Column
mct: Migration Create Table
mdt: Migration Drop Table
mac: Migration Add Column
mrc: Migration Remove Column
See Also Sami Samhuri’s information for a more complete description of these snippets
Steve Eichert: Migrations Explained