Reimplemented PostGIS spatial_version with cached_property

from django.db.backends.postgresql_psycopg2.base import DatabaseOperations

from django.db.utils import DatabaseError

from django.utils import six

from django.utils.functional import cached_property

from .models import GeometryColumns, SpatialRefSys

#### Classes used in constructing PostGIS spatial SQL ####

class PostGISOperator(SpatialOperation):

    compiler_module = 'django.contrib.gis.db.models.sql.compiler'

    name = 'postgis'

    postgis = True

    geom_func_prefix = 'ST_'

    version_regex = re.compile(r'^(?P<major>\d)\.(?P<minor1>\d)\.(?P<minor2>\d+)')

    valid_aggregates = dict([(k, None) for k in

                             ('Collect', 'Extent', 'Extent3D', 'MakeLine', 'Union')])

    def __init__(self, connection):

        super(PostGISOperations, self).__init__(connection)

        # Trying to get the PostGIS version because the function

        # signatures will depend on the version used.  The cost

        # here is a database query to determine the version, which

        # can be mitigated by setting `POSTGIS_VERSION` with a 3-tuple

        # comprising user-supplied values for the major, minor, and

        # subminor revision of PostGIS.

        try:

            if hasattr(settings, 'POSTGIS_VERSION'):

                vtup = settings.POSTGIS_VERSION

                if len(vtup) == 3:

                    # The user-supplied PostGIS version.

                    version = vtup

                else:

                    # This was the old documented way, but it's stupid to

                    # include the string.

                    version = vtup[1:4]

            else:

                vtup = self.postgis_version_tuple()

                version = vtup[1:]

            # Getting the prefix -- even though we don't officially support

            # PostGIS 1.2 anymore, keeping it anyway in case a prefix change

            # for something else is necessary.

            if version >= (1, 2, 2):

                prefix = 'ST_'

            else:

                prefix = ''

            self.geom_func_prefix = prefix

            self.spatial_version = version

        except DatabaseError:

            raise ImproperlyConfigured(

                'Cannot determine PostGIS version for database "%s". '

                'GeoDjango requires at least PostGIS version 1.3. '

                'Was the database created from a spatial database '

                'template?' % self.connection.settings_dict['NAME']

                )

        # TODO: Raise helpful exceptions as they become known.

        prefix = self.geom_func_prefix

        # PostGIS-specific operators. The commented descriptions of these

        # operators come from Section 7.6 of the PostGIS 1.4 documentation.

        self.geometry_operators = {

        self.geometry_functions.update(self.distance_functions)

        # Only PostGIS versions 1.3.4+ have GeoJSON serialization support.

        if version < (1, 3, 4):

        if self.spatial_version < (1, 3, 4):

            GEOJSON = False

        else:

            GEOJSON = prefix + 'AsGeoJson'

        # ST_ContainsProperly ST_MakeLine, and ST_GeoHash added in 1.4.

        if version >= (1, 4, 0):

        if self.spatial_version >= (1, 4, 0):

            GEOHASH = 'ST_GeoHash'

            BOUNDINGCIRCLE = 'ST_MinimumBoundingCircle'

            self.geometry_functions['contains_properly'] = PostGISFunction(prefix, 'ContainsProperly')

            GEOHASH, BOUNDINGCIRCLE = False, False

        # Geography type support added in 1.5.

        if version >= (1, 5, 0):

        if self.spatial_version >= (1, 5, 0):

            self.geography = True

            # Only a subset of the operators and functions are available

            # for the geography type.

            }

        # Native geometry type support added in PostGIS 2.0.

        if version >= (2, 0, 0):

        if self.spatial_version >= (2, 0, 0):

            self.geometry = True

        # Creating a dictionary lookup of all GIS terms for PostGIS.

        self.union = prefix + 'Union'

        self.unionagg = prefix + 'Union'

        if version >= (2, 0, 0):

        if self.spatial_version >= (2, 0, 0):

            self.extent3d = prefix + '3DExtent'

            self.length3d = prefix + '3DLength'

            self.perimeter3d = prefix + '3DPerimeter'

            self.length3d = prefix + 'Length3D'

            self.perimeter3d = prefix + 'Perimeter3D'

    @cached_property

    def spatial_version(self):

        """Determine the version of the PostGIS library."""

        # Trying to get the PostGIS version because the function

        # signatures will depend on the version used.  The cost

        # here is a database query to determine the version, which

        # can be mitigated by setting `POSTGIS_VERSION` with a 3-tuple

        # comprising user-supplied values for the major, minor, and

        # subminor revision of PostGIS.

        if hasattr(settings, 'POSTGIS_VERSION'):

            version = settings.POSTGIS_VERSION

        else:

            try:

                vtup = self.postgis_version_tuple()

            except DatabaseError:

                raise ImproperlyConfigured(

                    'Cannot determine PostGIS version for database "%s". '

                    'GeoDjango requires at least PostGIS version 1.3. '

                    'Was the database created from a spatial database '

                    'template?' % self.connection.settings_dict['NAME']

                    )

            version = vtup[1:]

        return version

    def check_aggregate_support(self, aggregate):

        """

        Checks if the given aggregate name is supported (that is, if it's

    # Routines for getting the OGC-compliant models.

    def geometry_columns(self):

        from django.contrib.gis.db.backends.postgis.models import GeometryColumns

        return GeometryColumns

    def spatial_ref_sys(self):

        from django.contrib.gis.db.backends.postgis.models import SpatialRefSys

        return SpatialRefSys