Allows radius to be a symbol representing a column in DB (#1107)

* Allows radius to be a symbol representing a column in DB

* Proposed changes by @alexreisner:

- Keeping branching condition consistent
- Not overwrite the method argument: ‘radius’
- Not assigning two variables in a single line, and
- Add code comments where needed

By “proposed” I meant, I copy/paste them from his comment. But we are
in agreement.

* Fixes broken test in PR

lib/geocoder/stores/active_record.rb

@@ -131,7 +131,11 @@ module Geocoder::Store
         distance_column = options.fetch(:distance_column) { 'distance' }
         bearing_column = options.fetch(:bearing_column)  { 'bearing' }
 
-        b = Geocoder::Calculations.bounding_box([latitude, longitude], radius, options)
+        # If radius is a DB column name, bounding box should include
+        # all rows within the maximum radius appearing in that column.
+        # Note: performance is dependent on variability of radii.
+        bb_radius = radius.is_a?(Symbol) ? maximum(radius) : radius
+        b = Geocoder::Calculations.bounding_box([latitude, longitude], bb_radius, options)
         args = b + [
           full_column_name(latitude_attribute),
           full_column_name(longitude_attribute)
@@ -142,7 +146,16 @@ module Geocoder::Store
           conditions = bounding_box_conditions
         else
           min_radius = options.fetch(:min_radius, 0).to_f
-          conditions = [bounding_box_conditions + " AND (#{distance}) BETWEEN ? AND ?", min_radius, radius]
+          # if radius is a DB column name,
+          # find rows between min_radius and value in column
+          if radius.is_a?(Symbol)
+            c = "BETWEEN ? AND #{radius}"
+            a = [min_radius]
+          else
+            c = "BETWEEN ? AND ?"
+            a = [min_radius, radius]
+          end
+          conditions = [bounding_box_conditions + " AND (#{distance}) " + c] + a
         end
         {
           :select => select_clause(options[:select],

test/db/migrate/001_create_test_schema.rb

@@ -15,6 +15,7 @@ class CreateTestSchema < superclass
         t.column :address, :string
         t.column :latitude, :decimal, :precision => 16, :scale => 6
         t.column :longitude, :decimal, :precision => 16, :scale => 6
+        t.column :radius_column, :decimal, :precision => 16, :scale => 6
       end
     end
 

test/test_helper.rb

@@ -75,6 +75,10 @@ else
         def primary_key
           :id
         end
+
+        def maximum(_field)
+          1.0
+        end
       end
     end
   end

test/unit/near_test.rb

@@ -18,6 +18,13 @@ class NearTest < GeocoderTestCase
     assert_match(/BETWEEN \? AND \?$/, result[:conditions][0])
   end
 
+  def test_near_scope_options_includes_radius_column_max_radius
+    omit("Not applicable to unextended SQLite") if using_unextended_sqlite?
+
+    result = Place.send(:near_scope_options, 1.0, 2.0, :radius_column)
+    assert_match(/BETWEEN \? AND radius_column$/, result[:conditions][0])
+  end
+
   def test_near_scope_options_includes_radius_default_min_radius
     omit("Not applicable to unextended SQLite") if using_unextended_sqlite?