5 files changed, 27 insertions, 13 deletions
diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index fc3906d395..189985b671 100644
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -304,21 +304,22 @@ module ActiveRecord #:nodoc:
   #   (or a bad spelling of an existing one).
   # * AssociationTypeMismatch - The object assigned to the association wasn't of the type
   #   specified in the association definition.
-  # * SerializationTypeMismatch - The serialized object wasn't of the class specified as the second parameter.
+  # * AttributeAssignmentError - An error occurred while doing a mass assignment through the
+  #   <tt>attributes=</tt> method.
+  #   You can inspect the +attribute+ property of the exception object to determine which attribute
+  #   triggered the error.
   # * ConnectionNotEstablished - No connection has been established. Use <tt>establish_connection</tt>
   #   before querying.
-  # * RecordNotFound - No record responded to the +find+ method. Either the row with the given ID doesn't exist
-  #   or the row didn't meet the additional restrictions. Some +find+ calls do not raise this exception to signal
-  #   nothing was found, please check its documentation for further details.
-  # * StatementInvalid - The database server rejected the SQL statement. The precise error is added in the message.
   # * MultiparameterAssignmentErrors - Collection of errors that occurred during a mass assignment using the
   #   <tt>attributes=</tt> method. The +errors+ property of this exception contains an array of
   #   AttributeAssignmentError
   #   objects that should be inspected to determine which attributes triggered the errors.
-  # * AttributeAssignmentError - An error occurred while doing a mass assignment through the
-  #   <tt>attributes=</tt> method.
-  #   You can inspect the +attribute+ property of the exception object to determine which attribute
-  #   triggered the error.
+  # * RecordInvalid - raised by save! and create! when the record is invalid.
+  # * RecordNotFound - No record responded to the +find+ method. Either the row with the given ID doesn't exist
+  #   or the row didn't meet the additional restrictions. Some +find+ calls do not raise this exception to signal
+  #   nothing was found, please check its documentation for further details.
+  # * SerializationTypeMismatch - The serialized object wasn't of the class specified as the second parameter.
+  # * StatementInvalid - The database server rejected the SQL statement. The precise error is added in the message.
   #
   # *Note*: The attributes listed are class-level attributes (accessible from both the class and instance level).
   # So it's possible to assign a logger to the class through <tt>Base.logger=</tt> which will then be used by all
diff --git a/activerecord/lib/active_record/explain.rb b/activerecord/lib/active_record/explain.rb
index 01cacf6153..313fdb3487 100644
--- a/activerecord/lib/active_record/explain.rb
+++ b/activerecord/lib/active_record/explain.rb
@@ -70,7 +70,7 @@ module ActiveRecord
     # the threshold is set to 0.
     #
     # As the name of the method suggests this only applies to automatic
-    # EXPLAINs, manual calls to +ActiveRecord::Relation#explain+ run.
+    # EXPLAINs, manual calls to <tt>ActiveRecord::Relation#explain</tt> run.
     def silence_auto_explain
       current = Thread.current
       original, current[:available_queries_for_explain] = current[:available_queries_for_explain], false
diff --git a/activerecord/lib/active_record/querying.rb b/activerecord/lib/active_record/querying.rb
index 95565b503a..29b8b2fb73 100644
--- a/activerecord/lib/active_record/querying.rb
+++ b/activerecord/lib/active_record/querying.rb
@@ -11,7 +11,7 @@ module ActiveRecord
     delegate :select, :group, :order, :except, :reorder, :limit, :offset, :joins,
              :where, :preload, :eager_load, :includes, :from, :lock, :readonly,
              :having, :create_with, :uniq, :references, :none, :to => :scoped
-    delegate :count, :average, :minimum, :maximum, :sum, :calculate, :pluck, :to => :scoped
+    delegate :count, :average, :minimum, :maximum, :sum, :calculate, :pluck, :ids, :to => :scoped
 
     # Executes a custom SQL query against your database and returns all the results. The results will
     # be returned as an array with columns requested encapsulated as attributes of the model you call
diff --git a/activerecord/lib/active_record/relation/calculations.rb b/activerecord/lib/active_record/relation/calculations.rb
index db894c8aa9..f388b75c05 100644
--- a/activerecord/lib/active_record/relation/calculations.rb
+++ b/activerecord/lib/active_record/relation/calculations.rb
@@ -139,6 +139,16 @@ module ActiveRecord
       end
     end
 
+    # Pluck all the ID's for the relation using the table's primary key
+    #
+    # Examples:
+    #
+    #   Person.ids # SELECT people.id FROM people
+    #   Person.joins(:companies).ids # SELECT people.id FROM PEOPLE INNER JOIN companies ON companies.person_id = people.id
+    def ids
+      pluck primary_key
+    end
+
     private
 
     def perform_calculation(operation, column_name, options = {})
diff --git a/activerecord/lib/active_record/relation/finder_methods.rb b/activerecord/lib/active_record/relation/finder_methods.rb
index 416b55f5c5..1ceb1949a4 100644
--- a/activerecord/lib/active_record/relation/finder_methods.rb
+++ b/activerecord/lib/active_record/relation/finder_methods.rb
@@ -217,8 +217,11 @@ module ActiveRecord
       if match.bang? && result.blank?
         raise RecordNotFound, "Couldn't find #{@klass.name} with #{conditions.to_a.collect {|p| p.join(' = ')}.join(', ')}"
       else
-        yield(result) if block_given?
-        result
+        if block_given? && result
+          yield(result)
+        else
+          result
+        end
       end
     end