from django.db.backends.postgresql_psycopg2.introspection import DatabaseIntrospection
from django.contrib.gis.gdal import OGRGeomType
class GeoIntrospectionError(Exception):
pass
class PostGISIntrospection(DatabaseIntrospection):
# Reverse dictionary for PostGIS geometry types not populated until
# introspection is actually performed.
postgis_types_reverse = {}
def get_postgis_types(self):
"""
Returns a dictionary with keys that are the PostgreSQL object
identification integers for the PostGIS geometry and/or
geography types (if supported).
"""
cursor = self.connection.cursor()
# The OID integers associated with the geometry type may
# be different across versions; hence, this is why we have
# to query the PostgreSQL pg_type table corresponding to the
# PostGIS custom data types.
oid_sql = 'SELECT "oid" FROM "pg_type" WHERE "typname" = %s'
try:
cursor.execute(oid_sql, ('geometry',))
GEOM_TYPE = cursor.fetchone()[0]
postgis_types = { GEOM_TYPE : 'GeometryField' }
if self.connection.ops.geography:
cursor.execute(oid_sql, ('geography',))
GEOG_TYPE = cursor.fetchone()[0]
# The value for the geography type is actually a tuple
# to pass in the `geography=True` keyword to the field
# definition.
postgis_types[GEOG_TYPE] = ('GeometryField', {'geography' : True})
finally:
cursor.close()
return postgis_types
def get_field_type(self, data_type, description):
if not self.postgis_types_reverse:
# If the PostGIS types reverse dictionary is not populated, do so
# now. In order to prevent unnecessary requests upon connection
# intialization, the `data_types_reverse` dictionary is not updated
# with the PostGIS custom types until introspection is actually
# performed -- in other words, when this function is called.
self.postgis_types_reverse = self.get_postgis_types()
self.data_types_reverse.update(self.postgis_types_reverse)
return super(PostGISIntrospection, self).get_field_type(data_type, description)
def get_geometry_type(self, table_name, geo_col):
"""
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,
"""
cursor = self.connection.cursor()
try:
try:
# First seeing if this geometry column is in the `geometry_columns`
cursor.execute('SELECT "coord_dimension", "srid", "type" '
'FROM "geometry_columns" '
'WHERE "f_table_name"=%s AND "f_geometry_column"=%s',
(table_name, geo_col))
row = cursor.fetchone()
if not row: raise GeoIntrospectionError
except GeoIntrospectionError:
if self.connection.ops.geography:
cursor.execute('SELECT "coord_dimension", "srid", "type" '
'FROM "geography_columns" '
'WHERE "f_table_name"=%s AND "f_geography_column"=%s',
(table_name, geo_col))
row = cursor.fetchone()
if not row:
raise Exception('Could not find a geometry or geography column for "%s"."%s"' %
(table_name, geo_col))
# OGRGeomType does not require GDAL and makes it easy to convert
# from OGC geom type name to Django field.
field_type = OGRGeomType(row[2]).django
# Getting any GeometryField keyword arguments that are not the default.
dim = row[0]
srid = row[1]
field_params = {}
if srid != 4326:
field_params['srid'] = srid
if dim != 2:
field_params['dim'] = dim
finally:
cursor.close()
return field_type, field_params
|