def get_queryset(self, feature_type: FeatureType) -> QuerySet:
"""Generate the queryset for the specific feature type.
This method can be overwritten in subclasses to define the returned data.
However, consider overwriting :meth:`compile_query` instead of simple data.
"""
queryset = feature_type.get_queryset()
# Apply filters
compiler = self.compile_query(feature_type, using=queryset.db)
if self.value_reference is not None:
if feature_type.resolve_element(
self.value_reference.xpath) is None:
raise InvalidParameterValue(
"valueReference",
f"Field '{self.value_reference.xpath}' does not exist.",
)
# For GetPropertyValue, adjust the query so only that value is requested.
# This makes sure XPath attribute selectors are already handled by the
# database query, instead of being a presentation-layer handling.
field = compiler.add_value_reference(self.value_reference)
queryset = compiler.filter_queryset(queryset,
feature_type=feature_type)
return queryset.values("pk", member=field)
else:
return compiler.filter_queryset(queryset,
feature_type=feature_type)
def decorate_queryset(cls, feature_type: FeatureType, queryset, output_crs,
**params):
"""Update the queryset to let the database render the GML output."""
value_reference = params["valueReference"]
match = feature_type.resolve_element(value_reference.xpath)
if match.child.is_geometry:
# Add 'gml_member' to point to the pre-rendered GML version.
return queryset.values(
"pk",
gml_member=AsGML(get_db_geometry_target(match, output_crs)))
else:
return queryset
def decorate_queryset(self, feature_type: FeatureType, queryset,
output_crs, **params):
"""Update the queryset to let the database render the GML output.
This is far more efficient then GeoDjango's logic, which performs a
C-API call for every single coordinate of a geometry.
"""
queryset = super().decorate_queryset(feature_type, queryset,
output_crs, **params)
# If desired, the entire FeatureCollection could be rendered
# in PostgreSQL as well: https://postgis.net/docs/ST_AsGeoJSON.html
match = feature_type.resolve_element(feature_type.geometry_field_name)
return queryset.defer(feature_type.geometry_field_name).annotate(
_as_db_geojson=AsGeoJSON(get_db_geometry_target(match, output_crs),
precision=16))