railsmigrations

Rails Migrations

Shameless copy of http://garrettsnider.backpackit.com/pub/367902

Rails Migration Cheat Sheet

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

What can I do?

    • 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

Problems? When the migration fails

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)")'

Snippets

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

Additional places to look:

Steve Eichert: Migrations Explained

Links to other public Backpack pages