95 lines
2.8 KiB
Python
95 lines
2.8 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.db.models.fields import GeoSelectFormatMixin
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from django.contrib.gis.geometry.backend import Geometry
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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 BaseField:
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empty_strings_allowed = True
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def get_db_converters(self, connection):
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return [self.from_db_value]
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def select_format(self, compiler, sql, params):
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return sql, params
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class AreaField(models.FloatField):
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"Wrapper for Area values."
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def __init__(self, area_att=None):
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self.area_att = area_att
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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 or not self.area_att:
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return value
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return getattr(value, self.area_att)
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def from_db_value(self, value, expression, connection, context):
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if connection.features.interprets_empty_strings_as_nulls and value == '':
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value = None
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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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if value is not None and self.area_att:
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value = Area(**{self.area_att: value})
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return value
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def get_internal_type(self):
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return 'AreaField'
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class DistanceField(BaseField):
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"Wrapper for Distance values."
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def __init__(self, distance_att):
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self.distance_att = distance_att
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def from_db_value(self, value, expression, connection, context):
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if value is not None:
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value = Distance(**{self.distance_att: value})
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return value
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def get_internal_type(self):
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return 'DistanceField'
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class GeomField(GeoSelectFormatMixin, BaseField):
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"""
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Wrapper for Geometry values. It is a lightweight alternative to
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using GeometryField (which requires an SQL query upon instantiation).
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"""
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# Hacky marker for get_db_converters()
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geom_type = None
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def from_db_value(self, value, expression, connection, context):
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if value is not None:
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value = Geometry(value)
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return value
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def get_internal_type(self):
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return 'GeometryField'
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class GMLField(BaseField):
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"""
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Wrapper for GML to be used by Oracle to ensure Database.LOB conversion.
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"""
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def get_internal_type(self):
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return 'GMLField'
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def from_db_value(self, value, expression, connection, context):
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return value
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