Fixed #25773 -- Deprecated the geos.MultiPolygon.cascaded_union property.

django/contrib/gis/geos/collections.py

@@ -3,6 +3,7 @@
  GeometryCollection, MultiPoint, MultiLineString, and MultiPolygon
 """
 import json
+import warnings
 from ctypes import byref, c_int, c_uint
 
 from django.contrib.gis.geos import prototypes as capi
@@ -13,6 +14,7 @@ from django.contrib.gis.geos.libgeos import get_pointer_arr
 from django.contrib.gis.geos.linestring import LinearRing, LineString
 from django.contrib.gis.geos.point import Point
 from django.contrib.gis.geos.polygon import Polygon
+from django.utils.deprecation import RemovedInDjango20Warning
 from django.utils.six.moves import range
 
 
@@ -135,6 +137,10 @@ class MultiPolygon(GeometryCollection):
     @property
     def cascaded_union(self):
         "Returns a cascaded union of this MultiPolygon."
+        warnings.warn(
+            "`cascaded_union` is deprecated, use the `unary_union` property instead.",
+            RemovedInDjango20Warning, 2
+        )
         return GEOSGeometry(capi.geos_cascaded_union(self.ptr), self.srid)
 
 # Setting the allowed types here since GeometryCollection is defined before