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class BaseSpatialOperations(object):
"""
This module holds the base `BaseSpatialBackend` object, which is
instantiated by each spatial database backend with the features
it has.
"""
truncate_params = {}
# Quick booleans for the type of this spatial backend, and
# an attribute for the spatial database version tuple (if applicable)
postgis = False
spatialite = False
mysql = False
oracle = False
spatial_version = None
# How the geometry column should be selected.
select = None
# Does the spatial database have a geometry or geography type?
geography = False
geometry = False
area = False
bounding_circle = False
centroid = False
difference = False
distance = False
distance_sphere = False
distance_spheroid = False
envelope = False
force_rhr = False
mem_size = False
num_geom = False
num_points = False
perimeter = False
perimeter3d = False
point_on_surface = False
polygonize = False
reverse = False
scale = False
snap_to_grid = False
sym_difference = False
transform = False
translate = False
union = False
# Aggregates
disallowed_aggregates = ()
geom_func_prefix = ''
# Mapping between Django function names and backend names, when names do not
# match; used in spatial_function_name().
function_names = {}
# Blacklist/set of known unsupported functions of the backend
unsupported_functions = {
'Area', 'AsGeoJSON', 'AsGML', 'AsKML', 'AsSVG',
'BoundingCircle', 'Centroid', 'Difference', 'Distance', 'Envelope',
'ForceRHR', 'GeoHash', 'Intersection', 'IsValid', 'Length', 'MakeValid',
'MemSize', 'NumGeometries', 'NumPoints', 'Perimeter', 'PointOnSurface',
'Reverse', 'Scale', 'SnapToGrid', 'SymDifference', 'Transform',
'Translate', 'Union',
}
# Serialization
geohash = False
geojson = False
gml = False
kml = False
svg = False
# Constructors
from_text = False
from_wkb = False
# Default conversion functions for aggregates; will be overridden if implemented
# for the spatial backend.
def convert_extent(self, box, srid):
raise NotImplementedError('Aggregate extent not implemented for this spatial backend.')
def convert_extent3d(self, box, srid):
raise NotImplementedError('Aggregate 3D extent not implemented for this spatial backend.')
# For quoting column values, rather than columns.
def geo_quote_name(self, name):
return "'%s'" % name
# GeometryField operations
def geo_db_type(self, f):
"""
Returns the database column type for the geometry field on
the spatial backend.
"""
raise NotImplementedError('subclasses of BaseSpatialOperations must provide a geo_db_type() method')
def get_distance(self, f, value, lookup_type):
"""
Returns the distance parameters for the given geometry field,
lookup value, and lookup type.
"""
raise NotImplementedError('Distance operations not available on this spatial backend.')
def get_geom_placeholder(self, f, value, compiler):
"""
Returns the placeholder for the given geometry field with the given
value. Depending on the spatial backend, the placeholder may contain a
stored procedure call to the transformation function of the spatial
backend.
"""
raise NotImplementedError('subclasses of BaseSpatialOperations must provide a geo_db_placeholder() method')
def check_expression_support(self, expression):
if isinstance(expression, self.disallowed_aggregates):
raise NotImplementedError(
"%s spatial aggregation is not supported by this database backend." % expression.name
)
super(BaseSpatialOperations, self).check_expression_support(expression)
def spatial_aggregate_name(self, agg_name):
raise NotImplementedError('Aggregate support not implemented for this spatial backend.')
def spatial_function_name(self, func_name):
if func_name in self.unsupported_functions:
raise NotImplementedError("This backend doesn't support the %s function." % func_name)
return self.function_names.get(func_name, self.geom_func_prefix + func_name)
# Routines for getting the OGC-compliant models.
def geometry_columns(self):
raise NotImplementedError('Subclasses of BaseSpatialOperations must provide a geometry_columns() method.')
def spatial_ref_sys(self):
raise NotImplementedError('subclasses of BaseSpatialOperations must a provide spatial_ref_sys() method')
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