Remove :timestamp column type

The `:timestamp` type for columns is unused. All database adapters treat
them as the same database type. All code in `ActiveRecord` which changes
its behavior based on the column's type acts the same in both cases.
However, when the type is passed to code that checks for the `:datetime`
type, but not `:timestamp` (such as XML serialization), the result is
unexpected behavior.

Existing schema definitions will continue to work, and the `timestamp`
type is transparently aliased to `datetime`.

1 files changed, 2 insertions, 2 deletions

diff --git a/activerecord/lib/active_record/attribute_methods/read.rb b/activerecord/lib/active_record/attribute_methods/read.rb
index d01e9aea59..979dfb207e 100644
--- a/activerecord/lib/active_record/attribute_methods/read.rb
+++ b/activerecord/lib/active_record/attribute_methods/read.rb
@@ -35,7 +35,7 @@ module ActiveRecord
 
       extend ActiveSupport::Concern
 
-      ATTRIBUTE_TYPES_CACHED_BY_DEFAULT = [:datetime, :timestamp, :time, :date]
+      ATTRIBUTE_TYPES_CACHED_BY_DEFAULT = [:datetime, :time, :date]
 
       included do
         class_attribute :attribute_types_cached_by_default, instance_writer: false
@@ -52,7 +52,7 @@ module ActiveRecord
         end
 
         # Returns the attributes which are cached. By default time related columns
-        # with datatype <tt>:datetime, :timestamp, :time, :date</tt> are cached.
+        # with datatype <tt>:datetime, :time, :date</tt> are cached.
         def cached_attributes
           @cached_attributes ||= columns.select { |c| cacheable_column?(c) }.map { |col| col.name }.to_set
         end