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module ActiveRecord
class IrreversibleMigration < ActiveRecordError
end
class Migration
class << self
def up() end
def down() end
private
def method_missing(method, *arguments, &block)
ActiveRecord::Base.connection.send(method, *arguments, &block)
end
end
end
class Migrator
class << self
def up(migrations_path, target_version = nil)
new(:up, migrations_path, target_version).migrate
end
def down(migrations_path, target_version = nil)
new(:down, migrations_path, target_version).migrate
end
def current_version
Base.connection.select_one("SELECT version FROM schema_info")["version"].to_i
end
end
def initialize(direction, migrations_path, target_version = nil)
@direction, @migrations_path, @target_version = direction, migrations_path, target_version
Base.connection.initialize_schema_information
end
def current_version
self.class.current_version
end
def migrate
migration_classes do |version, migration_class|
Base.logger.info("Reached target version: #{@target_version}") and break if reached_target_version?(version)
next if irrelevant_migration?(version)
Base.logger.info "Migrating to #{migration_class} (#{version})"
migration_class.send(@direction)
set_schema_version(version)
end
end
private
def migration_classes
for migration_file in migration_files
load(migration_file)
version, name = migration_version_and_name(migration_file)
yield version, migration_class(name)
end
end
def migration_files
files = Dir["#{@migrations_path}/[0-9]*_*.rb"]
down? ? files.reverse : files
end
def migration_class(migration_name)
migration_name.camelize.constantize
end
def migration_version_and_name(migration_file)
return *migration_file.scan(/([0-9]+)_([_a-z0-9]*).rb/).first
end
def set_schema_version(version)
Base.connection.update("UPDATE schema_info SET version = #{down? ? version.to_i - 1 : version.to_i}")
end
def up?
@direction == :up
end
def down?
@direction == :down
end
def reached_target_version?(version)
(up? && version.to_i - 1 == @target_version) || (down? && version.to_i == @target_version)
end
def irrelevant_migration?(version)
(up? && version.to_i <= current_version) || (down? && version.to_i > current_version)
end
end
end
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