Cloud9 ActiveRecord::ConnectionNotEstablished

Question

cloud9で　rails serverを実行すると以下のようなエラーが表示されました

ActiveRecord::ConnectionNotEstablished
No connection pool with id primary found.
Extracted source (around line #882):

880　def retrieve_connection(spec_name) #:nodoc:
881　pool = retrieve_connection_pool(spec_name)
882　raise ConnectionNotEstablished, "No connection pool with id #{spec_name} found." unless pool
883　 conn = pool.connection
884　 raise ConnectionNotEstablished, "No connection for #{spec_name} in connection pool" unless conn
885　conn
だれかわかる方教えてください