Ohio Revised Code Title XXVII. Courts Revised Code General Provisions Special Remedies § 2721.12

(A) Subject to division (B) of this section, when declaratory relief is sought under this chapter in an action or proceeding, all persons who have or claim any interest that would be affected by the declaration shall be made parties to the action or proceeding. Except as provided in division (B) of this section, a declaration shall not prejudice the rights of persons who are not made parties to the action or proceeding. In any action or proceeding that involves the validity of a municipal ordinance or franchise, the municipal corporation shall be made a party and shall be heard, and, if any statute or the ordinance or franchise is alleged to be unconstitutional, the attorney general also shall be served with a copy of the complaint in the action or proceeding and shall be heard. In any action or proceeding that involves the validity of a township resolution, the township shall be made a party and shall be heard.

(B) A declaratory judgment or decree that a court of record enters in an action or proceeding under this chapter between an insurer and a holder of a policy of liability insurance issued by the insurer and that resolves an issue as to whether the policy's coverage provisions extend to an injury, death, or loss to person or property that an insured under the policy allegedly tortiously caused shall be deemed to have the binding legal effect described in division (C)(2) of section 3929.06 of the Revised Code and to also have binding legal effect upon any person who seeks coverage as an assignee of the insured's rights under the policy in relation to the injury, death, or loss involved. This division applies whether or not an assignee is made a party to the action or proceeding for declaratory relief and notwithstanding any contrary common law principles of res judicata or adjunct principles of collateral estoppel.