code: func (m *Manager) IsParticipant(contractID string, name string) (isparticipant bool, err error) {
  	count, err := m.collection.Find(bson.M{"contractid": contractID, "parties.name": name}).Count()
  	if err != nil {
  		return
  	}
  	isparticipant = count != 0
  	return
  
  }
docs: //IsParticipant check if name is participant in contract with id contractID