Oneof rules

The OneofConstraints message type enables you to manage constraints for oneof fields in your protobuf messages.

required

If required is true, exactly one field of the oneof must be present. A validation error is returned if no fields in the oneof are present. The field itself may still be a default value; further constraints should be placed on the fields themselves to ensure they are valid values, such as min_len or gt.

oneof.required example

message MyMessage {
  oneof value {
    // Either `a` or `b` must be set. If `a` is set, it must also be
    // non-empty; whereas if `b` is set, it can still be an empty string.
    option (buf.validate.oneof).required = true;
    string a = 1 [(buf.validate.field).string.min_len = 1];
    string b = 2;
  }
}