Question

Prior to Rails 3.1, we could update the self.columns method of ActiveRecord::Base.
But that doesn’t seem to work now.

Now it seems if I remove a column from a table, I am forced to restart the Rails server. If I don’t I keep getting errors when INSERTs to the table happen. Rails still thinks the old column exists, even though it’s not in the database anymore.

Answer 1

Active Record does not support this out of the box, because it queries the database to get the columns of a model (unlike Merb’s ORM tool, Datamapper).

Nonetheless, you can patch this feature on Rails with (assuming, for instance, you want to ignore columns starting with “deprecated” string):

module ActiveRecord
  module ConnectionAdapters
    class SchemaCache

      def initialize(conn)
        @connection = conn
        @tables = {}

        @columns = Hash.new do |h, table_name|
          columns = conn.columns(table_name, "#{table_name} Columns").reject { |c| c.name.start_with? "deprecated"}
          h[table_name] = columns
        end

        @columns_hash = Hash.new do |h, table_name|
          h[table_name] = Hash[columns[table_name].map { |col|
            [col.name, col]
          }]
        end

        @primary_keys = Hash.new do |h, table_name|
          h[table_name] = table_exists?(table_name) ? conn.primary_key(table_name) : nil
        end
      end
    end
  end
end