Lesson 11: Manipulating stateful objects

When issued using a TypeDB driver, Get queries are used to retrieve stateful objects. They comprise a match clause and a get clause.

match
# match clause
get;

The TypeDBTransaction.query.get method is used to execute Get queries. It returns an iterator of results in the form of concept maps. A concept map is a collection of stateful objects that were matched by the variables in the query.

results: Iterator[ConceptMap] = transaction.query.fetch(QUERY)

The ConceptMap.get method is used to retrieve a stateful object from the concept map corresponding to a particular variable label. The object must then be cast to the appropriate type.

entity: Entity = result.get(VARIABLE_1).as_entity()
relation: Relation = result.get(VARIABLE_2).as_relation()
attribute: Attribute = result.get(VARIABLE_3).as_attribute()
entity_type: EntityType = result.get(VARIABLE_4).as_entity_type()
relation_type: RelationType = result.get(VARIABLE_5).as_relation_type()
attribute_type: AttributeType = result.get(VARIABLE_6).as_attribute_type()

One result is returned per variable for each match returned by the match clause. The set of results can be filtered before being returned using the get clause. The results are filtered for each unique combination of instances of the filter variables.

get $a, $b, $c;

The TypeDBTransaction.concepts property is used to access programmatic schema type retrieval methods. Its get_entity_type, get_relation_type, and get_attribute_type methods are used to retrieve entity, relation, and attribute types respectively. These methods return promises, and must be resolved using their resolve methods in order to obtain the responses.

entity_type: EntityType = transaction.concepts.get_entity_type(LABEL_1).resolve()
relation_type: RelationType = transaction.concepts.get_relation_type(LABEL_2).resolve()
attribute_type: AttributeType = transaction.concepts.get_attribute_type(LABEL_3).resolve()

The RelationType.get_relates method is used to retrieve the roles in a relation type.

role_types: Iterator[RoleType] = relation_type.get_relates(transaction)

The Type.get_instances method is used to retrieve all instances of a type.

entities: Iterator[Entity] = entity_type.get_instances(transaction)
relations: Iterator[Relation] = relation_type.get_instances(transaction)
attributes: Iterator[Attribute] = attribute_type.get_instances(transaction)

The Entity.get_has and Relation.get_has methods are used to retrieve the attributes owned by an entity or relation.

attributes: Iterator[Attribute] = entity.get_has(transaction)

The Entity.get_relations and Relation.get_relations methods are used to retrieve the relations that an entity or relation plays a role in.

relations: Iterator[Relation] = entity.get_relations(transaction)

The Attribute.get_owners method is used to retrieve the owners of an attribute.

owners: Iterator[Thing] = attribute.get_owners(transaction)

The Relation.get_players_by_role_type method is used to retrieve the roleplayers in a relation.

players: Iterator[Thing] = relation.get_players(transaction)

Because the owners of an attribute or the roleplayers in a relation can be both entities and relations, the objects returned by get_owners and get_players_by_role_type are of the generic Thing class and must be cast to the appropriate type.

def cast_thing(thing: Thing) -> Entity | Relation:
    if thing.is_entity():
        return thing.as_entity()
    if thing.is_relation():
        return thing.as_relation()

The EntityType.create, RelationType.create, and AttributeType.put methods are used to instantiate entity, relation, and attribute types respectively. When instantiating an attribute, its value must be provided as an argument.

entity: Entity = entity_type.create(transaction).resolve()
relation: Relation = relation_type.create(transaction).resolve()
attribute: Attribute = attribute_type.put(transaction, VALUE).resolve()

The Entity.set_has and Relation.set_has methods are used to give an entity or relation ownership of an attribute.

entity.set_has(attribute, transaction).resolve()

The Entity.unset_has and Relation.unset_has methods are used to remove ownership of an attribute from an entity or relation.

entity.unset_has(attribute, transaction).resolve()

The Relation.add_players method is used to add roleplayers to a relation.

relation.add_player(transaction, entity, role_type).resolve()

The Entity.delete and Relation.delete methods are used to delete entities and relations.

relation.delete(transaction).resolve()