code: private Boolean constraintsExistsForRelationship(String type, List<String> propertyNames) {
          Schema schema = db.schema();
  
          for (ConstraintDefinition constraintDefinition : Iterables.asList(schema.getConstraints(RelationshipType.withName(type)))) {
              List<String> properties = Iterables.asList(constraintDefinition.getPropertyKeys());
  
              if (properties.equals(propertyNames)) {
                  return true;
              }
          }
  
          return false;
      }
docs: Checks if a constraint exists for a given type and a list of properties
  This method checks for constraints on relationships
  
  @param type
  @param propertyNames
  @return true if the constraint exists otherwise it returns false