Optimize none? and one? relation query methods to use LIMIT and COUNT.

Use SQL COUNT and LIMIT 1 queries for none? and one? methods if no block or limit is given,
instead of loading the entire collection to memory. The any? and many? methods already
follow this behavior.

[Eugene Gilburg & Rafael Mendonça França]

3 files changed, 30 insertions, 2 deletions

diff --git a/activerecord/lib/active_record/associations/collection_association.rb b/activerecord/lib/active_record/associations/collection_association.rb
index 4b7591e15c..33e4516bd1 100644
--- a/activerecord/lib/active_record/associations/collection_association.rb
+++ b/activerecord/lib/active_record/associations/collection_association.rb
@@ -319,7 +319,8 @@ module ActiveRecord
       end
 
       # Returns true if the collections is not empty.
-      # Equivalent to +!collection.empty?+.
+      # If block given, loads all records and checks for one or more matches.
+      # Otherwise, equivalent to +!collection.empty?+.
       def any?
         if block_given?
           load_target.any? { |*block_args| yield(*block_args) }
@@ -329,7 +330,8 @@ module ActiveRecord
       end
 
       # Returns true if the collection has more than 1 record.
-      # Equivalent to +collection.size > 1+.
+      # If block given, loads all records and checks for two or more matches.
+      # Otherwise, equivalent to +collection.size > 1+.
       def many?
         if block_given?
           load_target.many? { |*block_args| yield(*block_args) }
diff --git a/activerecord/lib/active_record/null_relation.rb b/activerecord/lib/active_record/null_relation.rb
index 63ca29305d..fa6eaa7e64 100644
--- a/activerecord/lib/active_record/null_relation.rb
+++ b/activerecord/lib/active_record/null_relation.rb
@@ -30,10 +30,18 @@ module ActiveRecord
       true
     end
 
+    def none?
+      true
+    end
+
     def any?
       false
     end
 
+    def one?
+      false
+    end
+
     def many?
       false
     end
diff --git a/activerecord/lib/active_record/relation.rb b/activerecord/lib/active_record/relation.rb
index 8073eb99dd..6bbec7c0c0 100644
--- a/activerecord/lib/active_record/relation.rb
+++ b/activerecord/lib/active_record/relation.rb
@@ -271,6 +271,15 @@ module ActiveRecord
       end
     end
 
+    # Returns true if there are no records.
+    def none?
+      if block_given?
+        to_a.none? { |*block_args| yield(*block_args) }
+      else
+        empty?
+      end
+    end
+
     # Returns true if there are any records.
     def any?
       if block_given?
@@ -280,6 +289,15 @@ module ActiveRecord
       end
     end
 
+    # Returns true if there is exactly one record.
+    def one?
+      if block_given?
+        to_a.one? { |*block_args| yield(*block_args) }
+      else
+        limit_value ? to_a.one? : size == 1
+      end
+    end
+
     # Returns true if there is more than one record.
     def many?
       if block_given?