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/django/contrib/gis/db/backends/postgis/introspection.py

https://code.google.com/p/mango-py/
Python | 95 lines | 63 code | 6 blank | 26 comment | 7 complexity | 3489ecf57ce6f969ae387b48e6b1288f MD5 | raw file
 1from django.db.backends.postgresql_psycopg2.introspection import DatabaseIntrospection
 2from django.contrib.gis.gdal import OGRGeomType
 3
 4class GeoIntrospectionError(Exception):
 5    pass
 6
 7class 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