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"""
This module holds simple classes to convert geospatial values from the
database.
"""
from __future__ import unicode_literals
from decimal import Decimal
from django.contrib.gis.db.models.fields import GeoSelectFormatMixin
from django.contrib.gis.geometry.backend import Geometry
from django.contrib.gis.measure import Area, Distance
class BaseField(object):
empty_strings_allowed = True
def get_db_converters(self, connection):
return [self.from_db_value]
def select_format(self, compiler, sql, params):
return sql, params
class AreaField(BaseField):
"Wrapper for Area values."
def __init__(self, area_att=None):
self.area_att = area_att
def from_db_value(self, value, expression, connection, context):
if connection.features.interprets_empty_strings_as_nulls and value == '':
value = None
# If the database returns a Decimal, convert it to a float as expected
# by the Python geometric objects.
if isinstance(value, Decimal):
value = float(value)
# If the units are known, convert value into area measure.
if value is not None and self.area_att:
value = Area(**{self.area_att: value})
return value
def get_internal_type(self):
return 'AreaField'
class DistanceField(BaseField):
"Wrapper for Distance values."
def __init__(self, distance_att):
self.distance_att = distance_att
def from_db_value(self, value, expression, connection, context):
if value is not None:
value = Distance(**{self.distance_att: value})
return value
def get_internal_type(self):
return 'DistanceField'
class GeomField(GeoSelectFormatMixin, BaseField):
"""
Wrapper for Geometry values. It is a lightweight alternative to
using GeometryField (which requires an SQL query upon instantiation).
"""
# Hacky marker for get_db_converters()
geom_type = None
def from_db_value(self, value, expression, connection, context):
if value is not None:
value = Geometry(value)
return value
def get_internal_type(self):
return 'GeometryField'
class GMLField(BaseField):
"""
Wrapper for GML to be used by Oracle to ensure Database.LOB conversion.
"""
def get_internal_type(self):
return 'GMLField'
def from_db_value(self, value, expression, connection, context):
return value
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