How to Handle ActiveRecord Migrations in a Distributed Gem? - activerecord

Question

I am trying to write an app as a gem using ActiveRecord without Rails.
My problem is how to migrate a database already deployed by a user who will not have rake, etc. I have just distributed a schema.rb file and created the db from that. But now I want to allow users to update to a new gem and migrate their db.
I've looked at ActiveRecord::Migrator, but can't figure out how to use it.
For example, how would I tell ActiveRecord::Migrator to run all migrations up from whatever is the current_migration?
Anyone have any suggestions for how to go about this or a good reference?

Answer 1

After going at this fresh this morning I came up with the following which is working well:
module Byr
module Db
class << self
attr_accessor :config
attr_accessor :adapter
attr_accessor :db_name
end
def self.create_sqlite(config)
require 'sqlite3'
config = config.merge('database' => File.join(Byr.db_dir, config['database']))
ActiveRecord::Base.establish_connection(config)
end
def self.create_pg(config)
require 'pg'
# Connect to the postgres db to create the db
ActiveRecord::Base.establish_connection(config.merge('database' => 'postgres',
'schema_search_path' => 'public'))
begin
result = ActiveRecord::Base.connection.create_database(config['database'])
rescue PG::Error, ActiveRecord::StatementInvalid => e
unless e.message =~ /already exists/
raise
end
end
true
end
def self.mysql_creation_options(config)
#charset = ENV['CHARSET'] || 'utf8'
#collation = ENV['COLLATION'] || 'utf8_unicode_ci'
{:charset => (config['charset'] || #charset), :collation => (config['collation'] || #collation)}
end
def self.create_mysql(config)
require 'mysql2'
error_class = config['adapter'] =~ /mysql2/ ? Mysql2::Error : Mysql::Error
begin
ActiveRecord::Base.establish_connection(config.merge('database' => nil))
ActiveRecord::Base.connection.create_database(config['database'], mysql_creation_options(config))
ActiveRecord::Base.establish_connection(config)
rescue error_class => sqlerr
access_denied_error = 1045
if sqlerr.errno == access_denied_error
print "#{sqlerr.error}. \nPlease provide the root password for your mysql installation\n>"
root_password = $stdin.gets.strip
grant_statement = "GRANT ALL PRIVILEGES ON #{config['database']}.* " \
"TO '#{config['username']}'#'localhost' " \
"IDENTIFIED BY '#{config['password']}' WITH GRANT OPTION;"
ActiveRecord::Base.establish_connection(config.merge(
'database' => nil, 'username' => 'root', 'password' => root_password))
ActiveRecord::Base.connection.create_database(config['database'], mysql_creation_options(config))
ActiveRecord::Base.connection.execute grant_statement
ActiveRecord::Base.establish_connection(config)
else
Byr.warn sqlerr.error
Byr.warn "Couldn't create database for #{config.inspect}, charset: #{config['charset'] || #charset}, collation: #{config['collation'] || #collation}"
Byr.warn "(if you set the charset manually, make sure you have a matching collation)" if config['charset']
end
rescue ActiveRecord::StatementInvalid => e
ActiveRecord::Base.establish_connection(config)
end
end
def self.migrate
sys_migration_dir = File.join(Byr.install_dir, "db/migrate")
ActiveRecord::Migration.verbose = true
ActiveRecord::Migrator.migrate(sys_migration_dir)
end
def self.connected?
ActiveRecord::Base.connected? and
ActiveRecord::Base.connection_config[:adapter] == adapter
end
def self.disconnect
ActiveRecord::Base.connection_pool.disconnect!
end
# Really only for testing
def self.drop_db
ActiveRecord::Base.connection.drop_database(Byr.db_config)
end
end
end
Then, to initialize the db via the migrations:
module Byr
class << self
attr_accessor :install_dir
attr_accessor :db_dir
attr_accessor :config_dir
attr_accessor :config_file
attr_accessor :config
attr_accessor :db_config
attr_accessor :adapter
attr_accessor :database
def self.create_db
case db_config['adapter']
when /postgresql/
Byr::Db.create_pg(db_config)
when /sqlite/
Byr::Db.create_sqlite(db_config)
when /mysql/
Byr::Db.create_mysql(db_config)
else
raise ByrError "Your config.yml file specifies an unknown database adapter \'#{config['adapter']}\'"
end
end
def self.connect_db(reconnect = false)
unless reconnect
return true if Byr.connected?
end
ActiveRecord::Base.establish_connection(db_config)
end
def self.migrate
Byr::Db.migrate
end
def self.init(connect = true, adapter = nil)
adapter = canonicalize_adapter(adapter) if adapter
setup_db_config
if connect
create_db and connect_db and migrate
end
end
end
Some irrelevant parts of the code are omitted, but I hope this helps
someone else.
Much of the hard stuff comes from the rake tasks in rails.