def create(layer_wrapper: LayerWrapper, relation_manager: QgsRelationManager,
relation: QgsRelation) -> 'RelationalLayerWrapper':
referencing_layer: QgsVectorLayer = relation.referencingLayer()
try:
other_relation: QgsRelation = [r for r in relation_manager.referencingRelations(referencing_layer)
if r.id() != relation.id()][0]
except KeyError:
raise QaavaLayerError(tr('Relation error'), bar_msg(
tr('Relation {} does not contain referencing another layer', relation.name())))
relation_layer_wrapper = LayerWrapper.from_qgs_layer(referencing_layer)
a_pk: QgsField = referencing_layer.fields().toList()[relation.referencingFields()[0]]
m_pk_a: QgsField = layer_wrapper.get_layer().fields().toList()[relation.referencedFields()[0]]
fw_m_a = FieldWrapper.from_layer_wrapper(relation_layer_wrapper, a_pk, set(), '')
fw_a = FieldWrapper.from_layer_wrapper(layer_wrapper, m_pk_a, set(), '')
other_layer: QgsVectorLayer = other_relation.referencedLayer()
b_pk = other_layer.fields().toList()[other_relation.referencedFields()[0]]
m_pk_b = referencing_layer.fields().toList()[other_relation.referencingFields()[0]]
fw_m_b = FieldWrapper.from_layer_wrapper(relation_layer_wrapper, m_pk_b, set(), '')
other_layer_wrapper = LayerWrapper.from_qgs_layer(other_layer, relation_layer_wrapper, fw_m_b)
fw_b = FieldWrapper.from_layer_wrapper(other_layer_wrapper, b_pk, set(), '')
return RelationalLayerWrapper(referencing_layer.name(), other_layer.name(), layer_wrapper, fw_m_a,
fw_a, fw_m_b, fw_b)
