Rails changes schema.rb timestamps to datetimes

Question

This problem seems to happen all the time when working with other developers. We have a table created in a migration like so (backed by postgres):

create_table :subscription_events do |t|
  t.integer :subscriber_id
  t.text :source_url
  t.text :params
  t.text :session

  t.timestamps
end

Then at seemingly random points in time in the future after running rake db:migrate, Rails wants to update the schema.rb file to use datetime instead of timestamp, causing an additionally confusing reindentation of the whole create_table calls as well:

   create_table "subscription_events", :force => true do |t|
-    t.integer   "subscriber_id"
-    t.text      "source_url"
-    t.text      "params"
-    t.text      "session"
-    t.timestamp "created_at",    :limit => 6, :null => false
-    t.timestamp "updated_at",    :limit => 6, :null => false
+    t.integer  "subscriber_id"
+    t.text     "source_url"
+    t.text     "params"
+    t.text     "session"
+    t.datetime "created_at",    :null => false
+    t.datetime "updated_at",    :null => false
   end

What is causing this? Should we be checking in this modified file or just reset it every time?

Answer 1

This should not be causing any 'reindexation', because the :datetime and :timestamp migration types are both mapped to PostgreSQL's TIMESTAMP datatype.

This is likely caused as a result of the inherently unordered ActiveRecord::ConnectionAdapters::PostgreSQLAdapter::NATIVE_DATABASE_TYPES constant which is defined as a standard hash. When ActiveRecord searches for the first suitable match for 'TIMESTAMP', it may find either :datetime or :timestamp unpredictably (since both are matches).

In short, don't fuss about it as this shouldn't affect your data or schema in the least.

UPDATE

The rails 'datatype' used in the dump is found using the simplified_type method which will return :datetime for the TIMESTAMP datatype. More likely, you have upgraded your Rails version where the previous version had a different method for determining the datatype. Whatever the reason, this shouldn't affect you in any way.