Add a :limit option to specify the maximum number of records that can be...

Add a :limit option to specify the maximum number of records that can be processed by accepts_nested_attributes_for

activerecord/lib/active_record/nested_attributes.rb

@@ -3,6 +3,9 @@
 
 module ActiveRecord
   module NestedAttributes #:nodoc:
+    class TooManyRecords < ActiveRecordError
+    end
+
     extend ActiveSupport::Concern
 
     included do
@@ -203,6 +206,12 @@ module ClassMethods
       #   do not have a <tt>_destroy</tt> value that evaluates to true.
       #   Passing <tt>:all_blank</tt> instead of a Proc will create a proc
       #   that will reject a record where all the attributes are blank.
+      # [:limit]
+      #   Allows you to specify the maximum number of the associated records that
+      #   can be processes with the nested attributes. If the size of the
+      #   nested attributes array exceeds the specified limit, NestedAttributes::TooManyRecords
+      #   exception is raised. If omitted, any number associations can be processed.
+      #   Note that the :limit option is only applicable to one-to-many associations.
       #
       # Examples:
       #   # creates avatar_attributes=
@@ -214,7 +223,7 @@ module ClassMethods
       def accepts_nested_attributes_for(*attr_names)
         options = { :allow_destroy => false }
         options.update(attr_names.extract_options!)
-        options.assert_valid_keys(:allow_destroy, :reject_if)
+        options.assert_valid_keys(:allow_destroy, :reject_if, :limit)
 
         attr_names.each do |association_name|
           if reflection = reflect_on_association(association_name)
@@ -334,6 +343,10 @@ def assign_nested_attributes_for_collection_association(association_name, attrib
         raise ArgumentError, "Hash or Array expected, got #{attributes_collection.class.name} (#{attributes_collection.inspect})"
       end
 
+      if options[:limit] && attributes_collection.size > options[:limit]
+        raise TooManyRecords, "Maximum #{options[:limit]} records are allowed. Got #{attributes_collection.size} records instead."
+      end
+
       if attributes_collection.is_a? Hash
         attributes_collection = attributes_collection.sort_by { |index, _| index.to_i }.map { |_, attributes| attributes }
       end

activerecord/test/cases/nested_attributes_test.rb

@@ -603,3 +603,33 @@ def setup
 
   include NestedAttributesOnACollectionAssociationTests
 end
+
+class TestNestedAttributesLimit < ActiveRecord::TestCase
+  def setup
+    Pirate.accepts_nested_attributes_for :parrots, :limit => 2
+
+    @pirate = Pirate.create!(:catchphrase => "Don' botharrr talkin' like one, savvy?")
+  end
+
+  def teardown
+    Pirate.accepts_nested_attributes_for :parrots, :allow_destroy => true, :reject_if => proc { |attributes| attributes.empty? }
+  end
+
+  def test_limit_with_less_records
+    @pirate.attributes = { :parrots_attributes => { 'foo' => { :name => 'Big Big Love' } } }
+    assert_difference('Parrot.count') { @pirate.save! }
+  end
+
+  def test_limit_with_number_exact_records
+    @pirate.attributes = { :parrots_attributes => { 'foo' => { :name => 'Lovely Day' }, 'bar' => { :name => 'Blown Away' } } }
+    assert_difference('Parrot.count', 2) { @pirate.save! }
+  end
+
+  def test_limit_with_exceeding_records
+    assert_raises(ActiveRecord::NestedAttributes::TooManyRecords) do
+      @pirate.attributes = { :parrots_attributes => { 'foo' => { :name => 'Lovely Day' },
+                                                      'bar' => { :name => 'Blown Away' },
+                                                      'car' => { :name => 'The Happening' }} }
+    end
+  end
+end