Ticket #7934: f

Index: django/contrib/gis/db/models/manager.py
===================================================================
--- django/contrib/gis/db/models/manager.py     (revision 8066)
+++ django/contrib/gis/db/models/manager.py     (working copy)
@@ -1,5 +1,6 @@
 from django.db.models.manager import Manager
 from django.contrib.gis.db.models.query import GeoQuerySet
+from django.db import connection
 
 class GeoManager(Manager):
     "Overrides Manager to return Geographic QuerySets."
@@ -75,3 +76,53 @@
 
     def unionagg(self, *args, **kwargs):
         return self.get_query_set().unionagg(*args, **kwargs)
+
+    def nearest_to(self, point, number=5, geom_column='latlon',
+                   from_srid=2163, to_srid=2163,
+                   within_range=None):
+        """finds the model objects nearest to a given point
+        
+        `point` is a tuple of (x, y) in the spatial ref sys given by `from_srid`
+        
+        returns a list of tuples, sorted by increasing distance from the given `point`. 
+        each tuple being (model_object, dist), where distance is in the units of the 
+        spatial ref sys given by `to_srid`"""
+        if not isinstance(point, tuple):
+            raise TypeError
+        from string import Template
+        cursor = connection.cursor()
+        x, y = point
+        table = self.model._meta.db_table
+        distance_clause = ''
+        if within_range:
+            distance_clause = "AND (Distance(GeomFromText('POINT($x $y)', $from_srid), $geom_column) <= %f)" % within_range
+        sql = Template("""
+            SELECT id,
+                Length(Transform(SetSRID(MakeLine($geom_column, GeomFromText('POINT(' || $x || ' ' || $y || ')', $from_srid)), $from_srid), $to_srid))
+            
+
+            FROM $table
+            WHERE $geom_column IS NOT NULL %s
+            ORDER BY Distance(GeomFromText('POINT($x $y)', $from_srid), $geom_column) ASC
+            LIMIT $number;
+        """ % distance_clause)
+        cursor.execute(sql.substitute(locals()))
+        nearbys = cursor.fetchall()
+        # get a list of primary keys of the nearby model objects
+        ids = [p[0] for p in nearbys]
+        # get a list of distances from the model objects
+        dists = [p[1] for p in nearbys]
+        places = self.filter(id__in=ids)
+        # the QuerySet comes back in an undefined order; let's
+        # order it by distance from the given point
+        def order_by(objects, listing, name):
+            """a convenience method that takes a list of objects,
+            and orders them by comparing an attribute given by `name`
+            to a sorted listing of values of the same length."""
+            sorted = []
+            for i in listing:
+                for obj in objects:
+                    if getattr(obj, name) == i:
+                        sorted.append(obj)
+            return sorted
+        return zip(order_by(places, ids, 'id'), dists)