Django-1.2.1/django/contrib/gis/db/backends/postgis/introspection.py

   1 from django.db.backends.postgresql_psycopg2.introspection import DatabaseIntrospection
   2 from django.contrib.gis.gdal import OGRGeomType
   3
   4 class GeoIntrospectionError(Exception):
   5     pass
   6
   7 class PostGISIntrospection(DatabaseIntrospection):
   8     # Reverse dictionary for PostGIS geometry types not populated until
   9     # introspection is actually performed.
  10     postgis_types_reverse = {}
  11
  12     def get_postgis_types(self):
  13         """
  14         Returns a dictionary with keys that are the PostgreSQL object
  15         identification integers for the PostGIS geometry and/or
  16         geography types (if supported).
  17         """
  18         cursor = self.connection.cursor()
  19         # The OID integers associated with the geometry type may
  20         # be different across versions; hence, this is why we have
  21         # to query the PostgreSQL pg_type table corresponding to the
  22         # PostGIS custom data types.
  23         oid_sql = 'SELECT "oid" FROM "pg_type" WHERE "typname" = %s'
  24         try:
  25             cursor.execute(oid_sql, ('geometry',))
  26             GEOM_TYPE = cursor.fetchone()[0]
  27             postgis_types = { GEOM_TYPE : 'GeometryField' }
  28             if self.connection.ops.geography:
  29                 cursor.execute(oid_sql, ('geography',))
  30                 GEOG_TYPE = cursor.fetchone()[0]
  31                 # The value for the geography type is actually a tuple
  32                 # to pass in the `geography=True` keyword to the field
  33                 # definition.
  34                 postgis_types[GEOG_TYPE] = ('GeometryField', {'geography' : True})
  35         finally:
  36             cursor.close()
  37
  38         return postgis_types
  39
  40     def get_field_type(self, data_type, description):
  41         if not self.postgis_types_reverse:
  42             # If the PostGIS types reverse dictionary is not populated, do so
  43             # now.  In order to prevent unnecessary requests upon connection
  44             # intialization, the `data_types_reverse` dictionary is not updated
  45             # with the PostGIS custom types until introspection is actually
  46             # performed -- in other words, when this function is called.
  47             self.postgis_types_reverse = self.get_postgis_types()
  48             self.data_types_reverse.update(self.postgis_types_reverse)
  49         return super(PostGISIntrospection, self).get_field_type(data_type, description)
  50
  51     def get_geometry_type(self, table_name, geo_col):
  52         """
  53         The geometry type OID used by PostGIS does not indicate the particular
  54         type of field that a geometry column is (e.g., whether it's a
  55         PointField or a PolygonField).  Thus, this routine queries the PostGIS
  56         metadata tables to determine the geometry type,
  57         """
  58         cursor = self.connection.cursor()
  59         try:
  60             try:
  61                 # First seeing if this geometry column is in the `geometry_columns`
  62                 cursor.execute('SELECT "coord_dimension", "srid", "type" '
  63                                'FROM "geometry_columns" '
  64                                'WHERE "f_table_name"=%s AND "f_geometry_column"=%s',
  65                                (table_name, geo_col))
  66                 row = cursor.fetchone()
  67                 if not row: raise GeoIntrospectionError
  68             except GeoIntrospectionError:
  69                 if self.connection.ops.geography:
  70                     cursor.execute('SELECT "coord_dimension", "srid", "type" '
  71                                    'FROM "geography_columns" '
  72                                    'WHERE "f_table_name"=%s AND "f_geography_column"=%s',
  73                                    (table_name, geo_col))
  74                     row = cursor.fetchone()
  75
  76             if not row:
  77                 raise Exception('Could not find a geometry or geography column for "%s"."%s"' %
  78                                 (table_name, geo_col))
  79
  80             # OGRGeomType does not require GDAL and makes it easy to convert
  81             # from OGC geom type name to Django field.
  82             field_type = OGRGeomType(row[2]).django
  83
  84             # Getting any GeometryField keyword arguments that are not the default.
  85             dim = row[0]
  86             srid = row[1]
  87             field_params = {}
  88             if srid != 4326:
  89                 field_params['srid'] = srid
  90             if dim != 2:
  91                 field_params['dim'] = dim
  92         finally:
  93             cursor.close()
  94
  95         return field_type, field_params