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from django.contrib.gis.gdal import OGRGeomType
from django.db.backends.postgresql.introspection import DatabaseIntrospection
class PostGISIntrospection(DatabaseIntrospection):
postgis_oid_lookup = {} # Populated when introspection is performed.
ignored_tables = DatabaseIntrospection.ignored_tables + [
"geography_columns",
"geometry_columns",
"raster_columns",
"spatial_ref_sys",
"raster_overviews",
]
def get_field_type(self, data_type, description):
if not self.postgis_oid_lookup:
# Query PostgreSQL's pg_type table to determine the OID integers
# for the PostGIS data types used in reverse lookup (the integers
# may be different across versions). To prevent unnecessary
# requests upon connection initialization, the `data_types_reverse`
# dictionary isn't updated until introspection is performed here.
with self.connection.cursor() as cursor:
cursor.execute(
"SELECT oid, typname "
"FROM pg_type "
"WHERE typname IN ('geometry', 'geography')"
)
self.postgis_oid_lookup = dict(cursor.fetchall())
self.data_types_reverse.update(
(oid, "GeometryField") for oid in self.postgis_oid_lookup
)
return super().get_field_type(data_type, description)
def get_geometry_type(self, table_name, description):
"""
The geometry type OID used by PostGIS does not indicate the particular
type of field that a geometry column is (e.g., whether it's a
PointField or a PolygonField). Thus, this routine queries the PostGIS
metadata tables to determine the geometry type.
"""
with self.connection.cursor() as cursor:
cursor.execute(
"""
SELECT t.coord_dimension, t.srid, t.type FROM (
SELECT * FROM geometry_columns
UNION ALL
SELECT * FROM geography_columns
) AS t WHERE t.f_table_name = %s AND t.f_geometry_column = %s
""",
(table_name, description.name),
)
row = cursor.fetchone()
if not row:
raise Exception(
'Could not find a geometry or geography column for "%s"."%s"'
% (table_name, description.name)
)
dim, srid, field_type = row
# OGRGeomType does not require GDAL and makes it easy to convert
# from OGC geom type name to Django field.
field_type = OGRGeomType(field_type).django
# Getting any GeometryField keyword arguments that are not the default.
field_params = {}
if self.postgis_oid_lookup.get(description.type_code) == "geography":
field_params["geography"] = True
if srid != 4326:
field_params["srid"] = srid
if dim != 2:
field_params["dim"] = dim
return field_type, field_params
|
