Every assignment of a judgment shall be in writing, signed and acknowledged by the assignor, except that written notice of assignment shall be sufficient in the case of assignment under section 256.741. No assignment shall be valid as against a subsequent purchaser of the judgment in good faith for value, or against a creditor levying upon or attaching the same, unless it is filed with the court administrator and an entry is made in the docket. When filed and entered, no one but the assignee, the assignee’s agent, or attorney, shall be authorized to collect or enforce the judgment; provided, that the lien of an attorney on the judgment shall not be affected by the assignment.