Difference between Res Judicata and Order 2 Rule 2 of C.P.C.

Res Judicata	O. 2 r.2
This refers to plaintiff's duty to bring forward all the grounds of attack in support of his claim.	This requires the Plaintiff to claim all reliefs flowing from the same cause of action.
This refers to both the parties i.e. Plaintiff as well as Defendent and precludes a suit as well as defence.	This refers to only to the Plaintiff and bars a suit.

The doctrine of res judicata is often treated as a branch of the law of estoppel. Res judicata is really estoppel by verdict or estoppel by judgment. Even then the doctrine of res judicata differs in essential particulars from the doctrine of estoppel. Res Judicata results from a decision of the court, whereas, estoppel flows from the acts of parties. Res Judicata bars multiplicity of suits, whereas, estoppel prevents multiplicity of representations. Res Judicata ousts the jurisdiction of the court to try the case and to reopen the matter which is already adjudicated upon and thereby precludes an enquiry in limine. The estoppel is only a rule of evidence and shuts the mouth of a party.