70 lines
2.3 KiB
Python
70 lines
2.3 KiB
Python
"""
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This module holds simple classes to convert geospatial values from the
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database.
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"""
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from decimal import Decimal
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from django.contrib.gis.measure import Area, Distance
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from django.db import models
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class AreaField(models.FloatField):
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"Wrapper for Area values."
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def __init__(self, geo_field):
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super().__init__()
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self.geo_field = geo_field
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def get_prep_value(self, value):
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if not isinstance(value, Area):
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raise ValueError('AreaField only accepts Area measurement objects.')
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return value
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def get_db_prep_value(self, value, connection, prepared=False):
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if value is None:
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return
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area_att = connection.ops.get_area_att_for_field(self.geo_field)
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return getattr(value, area_att) if area_att else value
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def from_db_value(self, value, expression, connection):
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if value is None:
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return
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# If the database returns a Decimal, convert it to a float as expected
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# by the Python geometric objects.
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if isinstance(value, Decimal):
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value = float(value)
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# If the units are known, convert value into area measure.
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area_att = connection.ops.get_area_att_for_field(self.geo_field)
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return Area(**{area_att: value}) if area_att else value
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def get_internal_type(self):
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return 'AreaField'
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class DistanceField(models.FloatField):
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"Wrapper for Distance values."
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def __init__(self, geo_field):
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super().__init__()
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self.geo_field = geo_field
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def get_prep_value(self, value):
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if isinstance(value, Distance):
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return value
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return super().get_prep_value(value)
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def get_db_prep_value(self, value, connection, prepared=False):
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if not isinstance(value, Distance):
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return value
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distance_att = connection.ops.get_distance_att_for_field(self.geo_field)
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if not distance_att:
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raise ValueError('Distance measure is supplied, but units are unknown for result.')
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return getattr(value, distance_att)
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def from_db_value(self, value, expression, connection):
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if value is None:
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return
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distance_att = connection.ops.get_distance_att_for_field(self.geo_field)
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return Distance(**{distance_att: value}) if distance_att else value
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def get_internal_type(self):
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return 'DistanceField'
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