`establish_connection' undefined error


Whenever I run

rake db:schema:dump

i get the following error

rake aborted!
undefined local variable or method `establish_connection' for

Please help me in this regard. My database is oracle.

check your database connection
host: localhost
adapter: DB(oracle or mysql)
database: database name here
port: 3306
username: root
password: research
if ur not using IDE make sure there should be space after":" in each and everyline which you can see above