Fix undefined method `to_i' introduced since 3.2.8

This commit fixes a bug introduced in 96a13fc7 which breaks behaviour of
integer fields.

In 3.2.8, setting the value of an integer field to a non-integer (eg.
Array, Hash, etc.) would default to 1 (true) :

    # 3.2.8
    p = Post.new
    p.category_id = [ 1, 2 ]
    p.category_id # => 1
    p.category_id = { 3 => 4 }
    p.category_id # => 1

In 3.2.9 and above, this will raise a NoMethodError :

    # 3.2.9
    p = Post.new
    p.category_id = [ 1, 2 ]

    NoMethodError: undefined method `to_i' for [1, 2]:Array

Whilst at first blush this appear to be sensible, it combines in bad
ways with scoping.

For example, it is common to use scopes to control access to data :

    @collection = Posts.where(:category_id => [ 1, 2 ])
    @new_post = @collection.new

In 3.2.8, this would work as expected, creating a new Post object
(albeit with @new_post.category_id = 1). However, in 3.2.9 this will
cause the NoMethodError to be raised as above.

It is difficult to avoid triggering this error without descoping before
calling .new, breaking any apps running on 3.2.8 that rely on this
behaviour.

This patch deviates from 3.2.8 in that it does not retain the somewhat
spurious behaviour of setting the attribute to 1. Instead, it explicitly
sets these invalid values to nil :

    p = Post.new
    p.category_id = [ 1, 2 ]
    p.category_id # => nil

This also fixes the situation where a scope using an array will
"pollute" any newly instantiated records.

    @new_post = @collection.new
    @new_post.category_id # => nil

Finally, 3.2.8 exhibited a behaviour where setting an object to an
integer field caused it to be coerced to "1". This has not been
retained, as it is spurious and surprising in the same way that setting
Arrays and Heshes was :

    c = Category.find(6)
    p = Post.new

    # 3.2.8
    p.category_id = c
    p.category_id # => 1

    # This patch
    p.category_id = c
    p.category_id # => nil

This commit includes explicit test cases that expose the original issue
with calling new on a scope that uses an Array. As this is a common
situation, an explicit test case is the best way to prevent regressions
in the future.

It also updates and separates existing tests to be explicit about the
situation that is being tested (eg. AR objects vs. other objects vs.
non-integers)

4 files changed, 37 insertions, 8 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index db8fa303be..49473dc92a 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,6 +1,11 @@
 ## Rails 4.0.0 (unreleased) ##
 
-*   Rename `update_attributes` to `update`, keep `update_attributes` as an alias for `update` method. 
+*   Fix undefined method `to_i` when calling `new` on a scope that uses an Array.
+    Fixes #8718, #8734.
+
+    *Jason Stirk*
+
+*   Rename `update_attributes` to `update`, keep `update_attributes` as an alias for `update` method.
     This is a soft-deprecation for `update_attributes`, although it will still work without any
     deprecation message in 4.0 is recommended to start using `update` since `update_attributes` will be
     deprecated and removed in future versions of Rails.
diff --git a/activerecord/lib/active_record/connection_adapters/column.rb b/activerecord/lib/active_record/connection_adapters/column.rb
index fd36a5b075..51d3acaff8 100644
--- a/activerecord/lib/active_record/connection_adapters/column.rb
+++ b/activerecord/lib/active_record/connection_adapters/column.rb
@@ -206,7 +206,11 @@ module ActiveRecord
           when TrueClass, FalseClass
             value ? 1 : 0
           else
-            value.to_i
+            if value.respond_to?(:to_i)
+              value.to_i
+            else
+              nil
+            end
           end
         end
 
diff --git a/activerecord/test/cases/associations/belongs_to_associations_test.rb b/activerecord/test/cases/associations/belongs_to_associations_test.rb
index 97a3d57fe0..3a6da0e59f 100644
--- a/activerecord/test/cases/associations/belongs_to_associations_test.rb
+++ b/activerecord/test/cases/associations/belongs_to_associations_test.rb
@@ -63,6 +63,13 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
     assert_equal apple.id, citibank.firm_id
   end
 
+  def test_id_assignment
+    apple = Firm.create("name" => "Apple")
+    citibank = Account.create("credit_limit" => 10)
+    citibank.firm_id = apple
+    assert_nil citibank.firm_id
+  end
+
   def test_natural_assignment_with_primary_key
     apple = Firm.create("name" => "Apple")
     citibank = Client.create("name" => "Primary key client")
@@ -567,6 +574,11 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
     assert_equal new_firm.name, "Apple"
   end
 
+  def test_attributes_are_set_without_error_when_initialized_from_belongs_to_association_with_array_in_where_clause
+    new_account = Account.where(:credit_limit => [ 50, 60 ]).new
+    assert_nil new_account.credit_limit
+  end
+
   def test_reassigning_the_parent_id_updates_the_object
     client = companies(:second_client)
 
diff --git a/activerecord/test/cases/column_test.rb b/activerecord/test/cases/column_test.rb
index 2124c256fa..dc1b30261c 100644
--- a/activerecord/test/cases/column_test.rb
+++ b/activerecord/test/cases/column_test.rb
@@ -1,4 +1,5 @@
 require "cases/helper"
+require 'models/company'
 
 module ActiveRecord
   module ConnectionAdapters
@@ -40,13 +41,20 @@ module ActiveRecord
 
       def test_type_cast_non_integer_to_integer
         column = Column.new("field", nil, "integer")
-        assert_raises(NoMethodError) do
-          column.type_cast([])
-        end
+        assert_nil column.type_cast([1,2])
+        assert_nil column.type_cast({1 => 2})
+        assert_nil column.type_cast((1..2))
+      end
 
-        assert_raises(NoMethodError) do
-          column.type_cast(Object.new)
-        end
+      def test_type_cast_activerecord_to_integer
+        column = Column.new("field", nil, "integer")
+        firm = Firm.create(:name => 'Apple')
+        assert_nil column.type_cast(firm)
+      end
+
+      def test_type_cast_object_without_to_i_to_integer
+        column = Column.new("field", nil, "integer")
+        assert_nil column.type_cast(Object.new)
       end
 
       def test_type_cast_time