Fixed #25499 -- Added the ability to pass an expression in distance lookups

Thanks Bibhas Debnath for the report and Tim Graham for the review.

django/contrib/gis/db/backends/oracle/operations.py

@@ -195,7 +195,7 @@ class OracleOperations(BaseSpatialOperations, DatabaseOperations):
         """
         return 'MDSYS.SDO_GEOMETRY'
 
-    def get_distance(self, f, value, lookup_type):
+    def get_distance(self, f, value, lookup_type, **kwargs):
         """
         Returns the distance parameters given the value and the lookup type.
         On Oracle, geometry columns with a geodetic coordinate system behave

django/contrib/gis/db/backends/postgis/operations.py

@@ -34,14 +34,17 @@ class PostGISOperator(SpatialOperator):
 
 
 class PostGISDistanceOperator(PostGISOperator):
-    sql_template = '%(func)s(%(lhs)s, %(rhs)s) %(op)s %%s'
+    sql_template = '%(func)s(%(lhs)s, %(rhs)s) %(op)s %(value)s'
 
     def as_sql(self, connection, lookup, template_params, sql_params):
         if not lookup.lhs.output_field.geography and lookup.lhs.output_field.geodetic(connection):
             sql_template = self.sql_template
             if len(lookup.rhs) == 3 and lookup.rhs[-1] == 'spheroid':
                 template_params.update({'op': self.op, 'func': 'ST_Distance_Spheroid'})
-                sql_template = '%(func)s(%(lhs)s, %(rhs)s, %%s) %(op)s %%s'
+                sql_template = '%(func)s(%(lhs)s, %(rhs)s, %%s) %(op)s %(value)s'
+                # Using distance_spheroid requires the spheroid of the field as
+                # a parameter.
+                sql_params.insert(1, lookup.lhs.output_field._spheroid)
             else:
                 template_params.update({'op': self.op, 'func': 'ST_Distance_Sphere'})
             return sql_template % template_params, sql_params
@@ -226,7 +229,7 @@ class PostGISOperations(BaseSpatialOperations, DatabaseOperations):
                 geom_type = f.geom_type
             return 'geometry(%s,%d)' % (geom_type, f.srid)
 
-    def get_distance(self, f, dist_val, lookup_type):
+    def get_distance(self, f, dist_val, lookup_type, handle_spheroid=True):
         """
         Retrieve the distance parameters for the given geometry field,
         distance lookup value, and the distance lookup type.
@@ -236,11 +239,8 @@ class PostGISOperations(BaseSpatialOperations, DatabaseOperations):
         projected geometry columns.  In addition, it has to take into account
         the geography column type.
         """
-        # Getting the distance parameter and any options.
-        if len(dist_val) == 1:
-            value, option = dist_val[0], None
-        else:
-            value, option = dist_val
+        # Getting the distance parameter
+        value = dist_val[0]
 
         # Shorthand boolean flags.
         geodetic = f.geodetic(self.connection)
@@ -260,13 +260,17 @@ class PostGISOperations(BaseSpatialOperations, DatabaseOperations):
             # Assuming the distance is in the units of the field.
             dist_param = value
 
-        if (not geography and geodetic and lookup_type != 'dwithin'
-                and option == 'spheroid'):
-            # using distance_spheroid requires the spheroid of the field as
-            # a parameter.
-            return [f._spheroid, dist_param]
-        else:
-            return [dist_param]
+        params = [dist_param]
+        # handle_spheroid *might* be dropped in Django 2.0 as PostGISDistanceOperator
+        # also handles it (#25524).
+        if handle_spheroid and len(dist_val) > 1:
+            option = dist_val[1]
+            if (not geography and geodetic and lookup_type != 'dwithin'
+                    and option == 'spheroid'):
+                # using distance_spheroid requires the spheroid of the field as
+                # a parameter.
+                params.insert(0, f._spheroid)
+        return params
 
     def get_geom_placeholder(self, f, value, compiler):
         """

django/contrib/gis/db/backends/spatialite/operations.py

@@ -175,7 +175,7 @@ class SpatiaLiteOperations(BaseSpatialOperations, DatabaseOperations):
         """
         return None
 
-    def get_distance(self, f, value, lookup_type):
+    def get_distance(self, f, value, lookup_type, **kwargs):
         """
         Returns the distance parameters for the given geometry field,
         lookup value, and lookup type.  SpatiaLite only supports regular

django/contrib/gis/db/models/lookups.py

@@ -16,6 +16,10 @@ class GISLookup(Lookup):
     transform_func = None
     distance = False
 
+    def __init__(self, *args, **kwargs):
+        super(GISLookup, self).__init__(*args, **kwargs)
+        self.template_params = {}
+
     @classmethod
     def _check_geo_field(cls, opts, lookup):
         """
@@ -98,7 +102,8 @@ class GISLookup(Lookup):
         rhs_sql, rhs_params = self.process_rhs(compiler, connection)
         sql_params.extend(rhs_params)
 
-        template_params = {'lhs': lhs_sql, 'rhs': rhs_sql}
+        template_params = {'lhs': lhs_sql, 'rhs': rhs_sql, 'value': '%s'}
+        template_params.update(self.template_params)
         rhs_op = self.get_rhs_op(connection, rhs_sql)
         return rhs_op.as_sql(connection, self, template_params, sql_params)
 
@@ -302,18 +307,26 @@ gis_lookups['within'] = WithinLookup
 
 class DistanceLookupBase(GISLookup):
     distance = True
-    sql_template = '%(func)s(%(lhs)s, %(rhs)s) %(op)s %%s'
+    sql_template = '%(func)s(%(lhs)s, %(rhs)s) %(op)s %(value)s'
 
-    def get_db_prep_lookup(self, value, connection):
-        if isinstance(value, (tuple, list)):
-            if not 2 <= len(value) <= 3:
-                raise ValueError("2 or 3-element tuple required for '%s' lookup." % self.lookup_name)
-            params = [connection.ops.Adapter(value[0])]
-            # Getting the distance parameter in the units of the field.
-            params += connection.ops.get_distance(self.lhs.output_field, value[1:], self.lookup_name)
-            return ('%s', params)
+    def process_rhs(self, compiler, connection):
+        if not isinstance(self.rhs, (tuple, list)) or not 2 <= len(self.rhs) <= 3:
+            raise ValueError("2 or 3-element tuple required for '%s' lookup." % self.lookup_name)
+        params = [connection.ops.Adapter(self.rhs[0])]
+        # Getting the distance parameter in the units of the field.
+        dist_param = self.rhs[1]
+        if hasattr(dist_param, 'resolve_expression'):
+            dist_param = dist_param.resolve_expression(compiler.query)
+            sql, expr_params = compiler.compile(dist_param)
+            self.template_params['value'] = sql
+            params.extend(expr_params)
         else:
-            return super(DistanceLookupBase, self).get_db_prep_lookup(value, connection)
+            params += connection.ops.get_distance(
+                self.lhs.output_field, (dist_param,) + self.rhs[2:],
+                self.lookup_name, handle_spheroid=False
+            )
+        rhs = connection.ops.get_geom_placeholder(self.lhs.output_field, params[0], compiler)
+        return (rhs, params)
 
 
 class DWithinLookup(DistanceLookupBase):

docs/ref/contrib/gis/geoquerysets.txt

@@ -515,14 +515,20 @@ Distance lookups take the following form::
 
 The value passed into a distance lookup is a tuple; the first two
 values are mandatory, and are the geometry to calculate distances to,
-and a distance value (either a number in units of the field or a
-:class:`~django.contrib.gis.measure.Distance` object).  On every
-distance lookup but :lookup:`dwithin`, an optional
+and a distance value (either a number in units of the field, a
+:class:`~django.contrib.gis.measure.Distance` object, or a `query expression
+<ref/models/expressions>`).
+
+With PostGIS, on every distance lookup but :lookup:`dwithin`, an optional
 third element, ``'spheroid'``, may be included to tell GeoDjango
 to use the more accurate spheroid distance calculation functions on
 fields with a geodetic coordinate system (e.g., ``ST_Distance_Spheroid``
 would be used instead of ``ST_Distance_Sphere``).
 
+.. versionadded:: 1.10
+
+    The ability to pass an expression as the distance value was added.
+
 .. fieldlookup:: distance_gt
 
 distance_gt

docs/releases/1.10.txt

@@ -59,7 +59,8 @@ Minor features
 :mod:`django.contrib.gis`
 ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-* ...
+* :ref:`Distance lookups <distance-lookups>` now accept expressions as the
+  distance value parameter.
 
 :mod:`django.contrib.messages`
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

tests/gis_tests/distapp/models.py

@@ -21,6 +21,7 @@ class NamedModel(models.Model):
 class SouthTexasCity(NamedModel):
     "City model on projected coordinate system for South Texas."
     point = models.PointField(srid=32140)
+    radius = models.IntegerField(default=10000)
 
 
 class SouthTexasCityFt(NamedModel):
@@ -31,6 +32,7 @@ class SouthTexasCityFt(NamedModel):
 class AustraliaCity(NamedModel):
     "City model for Australia, using WGS84."
     point = models.PointField()
+    radius = models.IntegerField(default=10000)
 
 
 class CensusZipcode(NamedModel):

tests/gis_tests/distapp/tests.py

@@ -6,7 +6,7 @@ from django.contrib.gis.db.models.functions import (
 from django.contrib.gis.geos import GEOSGeometry, LineString, Point
 from django.contrib.gis.measure import D  # alias for Distance
 from django.db import connection
-from django.db.models import Q
+from django.db.models import F, Q
 from django.test import TestCase, ignore_warnings, skipUnlessDBFeature
 from django.utils.deprecation import RemovedInDjango20Warning
 
@@ -323,6 +323,31 @@ class DistanceTest(TestCase):
             cities = self.get_names(qs)
             self.assertEqual(cities, ['Adelaide', 'Hobart', 'Shellharbour', 'Thirroul'])
 
+    @skipUnlessDBFeature("supports_distances_lookups")
+    def test_distance_lookups_with_expression_rhs(self):
+        qs = SouthTexasCity.objects.filter(
+            point__distance_lte=(self.stx_pnt, F('radius')),
+        ).order_by('name')
+        self.assertEqual(
+            self.get_names(qs),
+            ['Bellaire', 'Downtown Houston', 'Southside Place', 'West University Place']
+        )
+
+        # With a combined expression
+        qs = SouthTexasCity.objects.filter(
+            point__distance_lte=(self.stx_pnt, F('radius') * 2),
+        ).order_by('name')
+        self.assertEqual(len(qs), 5)
+        self.assertIn('Pearland', self.get_names(qs))
+
+        # With spheroid param
+        if connection.features.supports_distance_geodetic:
+            hobart = AustraliaCity.objects.get(name='Hobart')
+            qs = AustraliaCity.objects.filter(
+                point__distance_lte=(hobart.point, F('radius') * 70, 'spheroid'),
+            ).order_by('name')
+            self.assertEqual(self.get_names(qs), ['Canberra', 'Hobart', 'Melbourne'])
+
     @skipUnlessDBFeature("has_area_method")
     @ignore_warnings(category=RemovedInDjango20Warning)
     def test_area(self):