6 files changed, 43 insertions, 3 deletions
diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 2c5066d2ee..6491f32f8f 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,4 +1,5 @@
-*   Remove ActiveRecord::Migrator.proper_table_name.
+*   Remove deprecated `ActiveRecord::Migrator.proper_table_name`. Use the
+    `proper_table_name` instance method on `ActiveRecord::Migration` instead.
 
     *Akshay Vishnoi*
 
diff --git a/activerecord/test/cases/associations/inverse_associations_test.rb b/activerecord/test/cases/associations/inverse_associations_test.rb
index 893030345f..a674a39d65 100644
--- a/activerecord/test/cases/associations/inverse_associations_test.rb
+++ b/activerecord/test/cases/associations/inverse_associations_test.rb
@@ -333,7 +333,7 @@ class InverseHasManyTests < ActiveRecord::TestCase
 
   def test_parent_instance_should_be_shared_within_create_block_of_new_child
     man = Man.first
-    interest = man.interests.build do |i|
+    interest = man.interests.create do |i|
       assert i.man.equal?(man), "Man of child should be the same instance as a parent"
     end
     assert interest.man.equal?(man), "Man of the child should still be the same instance as a parent"
diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index 8a9d31a7bb..871e1705f7 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,3 +1,23 @@
+*   Fixed `ActiveSupport::TimeWithZone#-` so precision is not unnecessarily lost
+    when working with objects with a nanosecond component.
+
+    `ActiveSupport::TimeWithZone#-` should return the same result as if we were
+    using `Time#-`:
+
+        Time.now.end_of_day - Time.now.beginning_of_day #=> 86399.999999999
+
+    Before:
+
+        Time.zone.now.end_of_day.nsec #=> 999999999
+        Time.zone.now.end_of_day - Time.zone.now.beginning_of_day #=> 86400.0
+
+    After:
+
+        Time.zone.now.end_of_day - Time.zone.now.beginning_of_day
+        #=> 86399.999999999
+
+    *Gordon Chan*
+
 *   Fixed precision error in NumberHelper when using Rationals.
 
     before:
diff --git a/activesupport/lib/active_support/time_with_zone.rb b/activesupport/lib/active_support/time_with_zone.rb
index 3155c0ab0f..4a0ed356b1 100644
--- a/activesupport/lib/active_support/time_with_zone.rb
+++ b/activesupport/lib/active_support/time_with_zone.rb
@@ -262,7 +262,7 @@ module ActiveSupport
       # If we're subtracting a Duration of variable length (i.e., years, months, days), move backwards from #time,
       # otherwise move backwards #utc, for accuracy when moving across DST boundaries
       if other.acts_like?(:time)
-        utc.to_f - other.to_f
+        to_time - other.to_time
       elsif duration_of_variable_length?(other)
         method_missing(:-, other)
       else
diff --git a/activesupport/test/core_ext/time_with_zone_test.rb b/activesupport/test/core_ext/time_with_zone_test.rb
index 7fe4d4a6b2..6d779bf3d5 100644
--- a/activesupport/test/core_ext/time_with_zone_test.rb
+++ b/activesupport/test/core_ext/time_with_zone_test.rb
@@ -246,16 +246,31 @@ class TimeWithZoneTest < ActiveSupport::TestCase
     assert_equal  86_400.0,  ActiveSupport::TimeWithZone.new( Time.utc(2000, 1, 2), ActiveSupport::TimeZone['Hawaii'] ) - Time.utc(2000, 1, 1)
   end
 
+  def test_minus_with_time_precision
+    assert_equal  86_399.999999998,  ActiveSupport::TimeWithZone.new( Time.utc(2000, 1, 2, 23, 59, 59, Rational(999999999, 1000)), ActiveSupport::TimeZone['UTC'] ) - Time.utc(2000, 1, 2, 0, 0, 0, Rational(1, 1000))
+    assert_equal  86_399.999999998,  ActiveSupport::TimeWithZone.new( Time.utc(2000, 1, 2, 23, 59, 59, Rational(999999999, 1000)), ActiveSupport::TimeZone['Hawaii'] ) - Time.utc(2000, 1, 2, 0, 0, 0, Rational(1, 1000))
+  end
+
   def test_minus_with_time_with_zone
     twz1 = ActiveSupport::TimeWithZone.new( Time.utc(2000, 1, 1), ActiveSupport::TimeZone['UTC'] )
     twz2 = ActiveSupport::TimeWithZone.new( Time.utc(2000, 1, 2), ActiveSupport::TimeZone['UTC'] )
     assert_equal  86_400.0,  twz2 - twz1
   end
 
+  def test_minus_with_time_with_zone_precision
+    twz1 = ActiveSupport::TimeWithZone.new( Time.utc(2000, 1, 1, 0, 0, 0, Rational(1, 1000)), ActiveSupport::TimeZone['UTC'] )
+    twz2 = ActiveSupport::TimeWithZone.new( Time.utc(2000, 1, 1, 23, 59, 59, Rational(999999999, 1000)), ActiveSupport::TimeZone['UTC'] )
+    assert_equal  86_399.999999998,  twz2 - twz1
+  end
+
   def test_minus_with_datetime
     assert_equal  86_400.0,  ActiveSupport::TimeWithZone.new( Time.utc(2000, 1, 2), ActiveSupport::TimeZone['UTC'] ) - DateTime.civil(2000, 1, 1)
   end
 
+  def test_minus_with_datetime_precision
+    assert_equal  86_399.999999999,  ActiveSupport::TimeWithZone.new( Time.utc(2000, 1, 1, 23, 59, 59, Rational(999999999, 1000)), ActiveSupport::TimeZone['UTC'] ) - DateTime.civil(2000, 1, 1)
+  end
+
   def test_minus_with_wrapped_datetime
     assert_equal  86_400.0,  ActiveSupport::TimeWithZone.new( DateTime.civil(2000, 1, 2), ActiveSupport::TimeZone['UTC'] ) - Time.utc(2000, 1, 1)
     assert_equal  86_400.0,  ActiveSupport::TimeWithZone.new( DateTime.civil(2000, 1, 2), ActiveSupport::TimeZone['UTC'] ) - DateTime.civil(2000, 1, 1)
diff --git a/guides/source/getting_started.md b/guides/source/getting_started.md
index d9619bbc21..e088abc150 100644
--- a/guides/source/getting_started.md
+++ b/guides/source/getting_started.md
@@ -623,6 +623,8 @@ method returns an `ActiveSupport::HashWithIndifferentAccess` object, which
 allows you to access the keys of the hash using either strings or symbols. In
 this situation, the only parameters that matter are the ones from the form.
 
+TIP: Ensure you have a firm grasp of the `params` method, as you'll use it fairly regularly. Let's consider an example URL: **http://www.example.com/?username=dhh&email=dhh@email.com**. In this URL, `params[:username]` would equal "dhh" and `params[:email]` would equal "dhh@email.com".
+
 If you re-submit the form one more time you'll now no longer get the missing
 template error. Instead, you'll see something that looks like the following:
 
@@ -739,6 +741,8 @@ database columns. In the first line we do just that (remember that
 `@article.save` is responsible for saving the model in the database. Finally,
 we redirect the user to the `show` action, which we'll define later.
 
+TIP: You might be wondering why the `A` in `Article.new` is capitalized above, whereas most other references to articles in this guide have used lowercase. In this context, we are referring to the class named `Article` that is defined in `\models\article.rb`. Class names in Ruby must begin with a capital letter.
+
 TIP: As we'll see later, `@article.save` returns a boolean indicating whether
 the article was saved or not.