Map<String, ManagedPropertyDescription> properties

All properties (relationships and attributes) of this entity.

The string key is the name of the property, case-sensitive. Values will be instances of either ManagedAttributeDescription or ManagedRelationshipDescription. This is the concatenation of attributes and relationships.

Source 

Map<String, ManagedPropertyDescription> get properties {
  var all =
      new Map.from(attributes) as Map<String, ManagedPropertyDescription>;
  if (relationships != null) {
    all.addAll(relationships);
  }
  return all;
}