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1 """ |
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2 The GeometryProxy object, allows for lazy-geometries. The proxy uses |
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3 Python descriptors for instantiating and setting Geometry objects |
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4 corresponding to geographic model fields. |
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5 |
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6 Thanks to Robert Coup for providing this functionality (see #4322). |
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7 """ |
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8 |
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9 from types import NoneType, StringType, UnicodeType |
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10 |
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11 class GeometryProxy(object): |
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12 def __init__(self, klass, field): |
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13 """ |
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14 Proxy initializes on the given Geometry class (not an instance) and |
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15 the GeometryField. |
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16 """ |
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17 self._field = field |
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18 self._klass = klass |
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19 |
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20 def __get__(self, obj, type=None): |
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21 """ |
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22 This accessor retrieves the geometry, initializing it using the geometry |
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23 class specified during initialization and the HEXEWKB value of the field. |
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24 Currently, only GEOS or OGR geometries are supported. |
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25 """ |
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26 # Getting the value of the field. |
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27 geom_value = obj.__dict__[self._field.attname] |
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28 |
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29 if isinstance(geom_value, self._klass): |
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30 geom = geom_value |
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31 elif (geom_value is None) or (geom_value==''): |
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32 geom = None |
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33 else: |
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34 # Otherwise, a Geometry object is built using the field's contents, |
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35 # and the model's corresponding attribute is set. |
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36 geom = self._klass(geom_value) |
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37 setattr(obj, self._field.attname, geom) |
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38 return geom |
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39 |
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40 def __set__(self, obj, value): |
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41 """ |
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42 This accessor sets the proxied geometry with the geometry class |
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43 specified during initialization. Values of None, HEXEWKB, or WKT may |
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44 be used to set the geometry as well. |
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45 """ |
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46 # The OGC Geometry type of the field. |
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47 gtype = self._field._geom |
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48 |
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49 # The geometry type must match that of the field -- unless the |
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50 # general GeometryField is used. |
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51 if isinstance(value, self._klass) and (str(value.geom_type).upper() == gtype or gtype == 'GEOMETRY'): |
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52 # Assigning the SRID to the geometry. |
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53 if value.srid is None: value.srid = self._field._srid |
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54 elif isinstance(value, (NoneType, StringType, UnicodeType)): |
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55 # Set with None, WKT, or HEX |
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56 pass |
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57 else: |
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58 raise TypeError('cannot set %s GeometryProxy with value of type: %s' % (obj.__class__.__name__, type(value))) |
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59 |
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60 # Setting the objects dictionary with the value, and returning. |
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61 obj.__dict__[self._field.attname] = value |
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62 return value |