Multi-schema support for migrations in Rails

schema_utils.rb

#
# http://www.developerit.com/2010/05/07/creating-a-multi-tenant-application-using-postgresqls-schemas-and-rails
#
module SchemaUtils
  def self.add_schema_to_path(schema)
    conn = ActiveRecord::Base.connection
    conn.execute "SET search_path TO #{schema}, #{conn.schema_search_path}"
  end

  def self.reset_search_path
    conn = ActiveRecord::Base.connection
    conn.execute "SET search_path TO #{conn.schema_search_path}"
  end

  def self.create_and_migrate_schema(schema_name)
    conn = ActiveRecord::Base.connection

    schemas = conn.select_values("select * from pg_namespace where nspname != 'information_schema' AND nspname NOT LIKE 'pg%'")

    if schemas.include?(schema_name)
      tables = conn.tables
      Rails.logger.info "#{schema_name} exists already with these tables #{tables.inspect}"
    else
      Rails.logger.info "About to create #{schema_name}"
      conn.execute "create schema #{schema_name}"
    end

    # Save the old search path so we can set it back at the end of this method
    old_search_path = conn.schema_search_path

    # Tried to set the search path like in the methods above (from Guy Naor)
    # conn.execute "SET search_path TO #{schema_name}"
    # But the connection itself seems to remember the old search path.
    # If set this way, it works.
    conn.schema_search_path = schema_name

    # Directly from databases.rake.
    # In Rails 2.3.5 databases.rake can be found in railties/lib/tasks/databases.rake
    file = "#{Rails.root}/db/schema.rb"
    if File.exists?(file)
      Rails.logger.info "About to load the schema #{file}"
      load(file)
    else
      abort %{#{file} doesn't exist yet. It's possible that you just ran a migration!}
    end

    Rails.logger.info "About to set search path back to #{old_search_path}."
    conn.schema_search_path = old_search_path
  end

end