Viewing file:  conversion.py (2.34 KB) -rw-r--r--
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"""
This module holds simple classes to convert geospatial values from the
database.
"""
from decimal import Decimal
from django.contrib.gis.measure import Area, Distance
from django.db import models
class AreaField(models.FloatField):
"Wrapper for Area values."
def __init__(self, geo_field):
super().__init__()
self.geo_field = geo_field
def get_prep_value(self, value):
if not isinstance(value, Area):
raise ValueError('AreaField only accepts Area measurement objects.')
return value
def get_db_prep_value(self, value, connection, prepared=False):
if value is None:
return
area_att = connection.ops.get_area_att_for_field(self.geo_field)
return getattr(value, area_att) if area_att else value
def from_db_value(self, value, expression, connection):
if value is None:
return
# 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.
area_att = connection.ops.get_area_att_for_field(self.geo_field)
return Area(**{area_att: value}) if area_att else value
def get_internal_type(self):
return 'AreaField'
class DistanceField(models.FloatField):
"Wrapper for Distance values."
def __init__(self, geo_field):
super().__init__()
self.geo_field = geo_field
def get_prep_value(self, value):
if isinstance(value, Distance):
return value
return super().get_prep_value(value)
def get_db_prep_value(self, value, connection, prepared=False):
if not isinstance(value, Distance):
return value
distance_att = connection.ops.get_distance_att_for_field(self.geo_field)
if not distance_att:
raise ValueError('Distance measure is supplied, but units are unknown for result.')
return getattr(value, distance_att)
def from_db_value(self, value, expression, connection):
if value is None:
return
distance_att = connection.ops.get_distance_att_for_field(self.geo_field)
return Distance(**{distance_att: value}) if distance_att else value
def get_internal_type(self):
return 'DistanceField'
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