find_by

# File activerecord/lib/active_record/core.rb, line 162
      def find_by(*args) # :nodoc:
        return super if current_scope || !(Hash === args.first) || reflect_on_all_aggregations.any?
        return super if default_scopes.any?

        hash = args.first

        return super if hash.values.any? { |v|
          v.nil? || Array === v || Hash === v
        }

        # We can't cache Post.find_by(author: david) ...yet
        return super unless hash.keys.all? { |k| columns_hash.has_key?(k.to_s) }

        key  = hash.keys

        klass = self
        s = find_by_statement_cache[key] || find_by_statement_cache.synchronize {
          find_by_statement_cache[key] ||= StatementCache.create(connection) { |params|
            wheres = key.each_with_object({}) { |param,o|
              o[param] = params.bind
            }
            klass.where(wheres).limit(1)
          }
        }
        begin
          s.execute(hash.values, self, connection).first
        rescue TypeError => e
          raise ActiveRecord::StatementInvalid.new(e.message, e)
        rescue RangeError
          nil
        end
      end