Rather than raising ThrowResult when construct_limited_ids_conditions comes up empty, set the relation to NullRelation and rely on its results.

This will help avoid errors like 2fcafee250ee2, because in most cases NullRelation will do the right thing. Minor bonus is avoiding the use of exceptions for flow control.

1 files changed, 15 insertions, 13 deletions

diff --git a/activerecord/lib/active_record/relation/finder_methods.rb b/activerecord/lib/active_record/relation/finder_methods.rb
index ba222aac93..f0edef58bf 100644
--- a/activerecord/lib/active_record/relation/finder_methods.rb
+++ b/activerecord/lib/active_record/relation/finder_methods.rb
@@ -160,8 +160,9 @@ module ActiveRecord
       conditions = conditions.id if Base === conditions
       return false if !conditions
 
-      join_dependency = construct_join_dependency
-      relation = construct_relation_for_association_find(join_dependency)
+      relation = construct_relation_for_association_find(construct_join_dependency)
+      return false if ActiveRecord::NullRelation === relation
+
       relation = relation.except(:select, :order).select("1 AS one").limit(1)
 
       case conditions
@@ -172,8 +173,6 @@ module ActiveRecord
       end
 
       connection.select_value(relation, "#{name} Exists", relation.bind_values)
-    rescue ThrowResult
-      false
     end
 
     # This method is called whenever no records are found with either a single
@@ -203,10 +202,12 @@ module ActiveRecord
     def find_with_associations
       join_dependency = construct_join_dependency
       relation = construct_relation_for_association_find(join_dependency)
-      rows = connection.select_all(relation, 'SQL', relation.bind_values.dup)
-      join_dependency.instantiate(rows)
-    rescue ThrowResult
-      []
+      if ActiveRecord::NullRelation === relation
+        []
+      else
+        rows = connection.select_all(relation, 'SQL', relation.bind_values.dup)
+        join_dependency.instantiate(rows)
+      end
     end
 
     def construct_join_dependency(joins = [])
@@ -230,21 +231,22 @@ module ActiveRecord
       if using_limitable_reflections?(join_dependency.reflections)
         relation
       else
-        relation.where!(construct_limited_ids_condition(relation)) if relation.limit_value
+        if relation.limit_value
+          limited_ids = limited_ids_for(relation)
+          limited_ids.empty? ? relation.none! : relation.where!(table[primary_key].in(limited_ids))
+        end
         relation.except(:limit, :offset)
       end
     end
 
-    def construct_limited_ids_condition(relation)
+    def limited_ids_for(relation)
       values = @klass.connection.columns_for_distinct(
         "#{quoted_table_name}.#{quoted_primary_key}", relation.order_values)
 
       relation = relation.except(:select).select(values).distinct!
 
       id_rows = @klass.connection.select_all(relation.arel, 'SQL', relation.bind_values)
-      ids_array = id_rows.map {|row| row[primary_key]}
-
-      ids_array.empty? ? raise(ThrowResult) : table[primary_key].in(ids_array)
+      id_rows.map {|row| row[primary_key]}
     end
 
     def find_with_ids(*ids)