1. @override
dynamic convertToPrimitiveValue(value)

Converts a value from a more complex value into a primitive value according to this instance's definition.

This method takes a Dart representation of a value and converts it to something that can be used elsewhere (e.g. an HTTP body or database query). How this value is computed depends on this instance's definition.

Source 

@override
dynamic convertToPrimitiveValue(dynamic value) {
  if (value is ManagedSet) {
    return value
        .map((ManagedObject innerValue) => innerValue.asMap())
        .toList();
  } else if (value is ManagedObject) {
    // If we're only fetching the foreign key, don't do a full asMap
    if (relationshipType == ManagedRelationshipType.belongsTo
    && value.backingMap.length == 1
    && value.backingMap.containsKey(destinationEntity.primaryKey)) {
      return {destinationEntity.primaryKey: value[destinationEntity.primaryKey]};
    }

    return value.asMap();
  } else if (value == null) {
    return null;
  }

  throw new QueryException(QueryExceptionEvent.requestFailure,
      message: "Invalid value '$value' for property '$entity.$name', "
          "expected '${MirrorSystem.getName(destinationEntity.instanceType.simpleName)}'");
}