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