Migration to add close-time to changesets. This replaces the boolean 'open' attribute. Added checks to ensure that the maximum lifetime and number of changes in a changeset are enforced. Added some tests.

db/migrate/023_add_end_time_to_changesets.rb

@@ -0,0 +1,34 @@
+class AddEndTimeToChangesets < ActiveRecord::Migration
+  def self.up
+    # swap the boolean closed-or-not for a time when the changeset will
+    # close or has closed.
+    add_column(:changesets, :closed_at, :datetime, :null => false)
+    
+    # it appears that execute will only accept string arguments, so
+    # this is an ugly, ugly hack to get some sort of mysql/postgres
+    # independence. now i have to go wash my brain with bleach.
+    execute("update changesets set closed_at=(now()-'1 hour') where open=(1=0)")
+    execute("update changesets set closed_at=(now()+'1 hour') where open=(1=1)")
+
+    # remove the open column as it is unnecessary now and denormalises 
+    # the table.
+    remove_column :changesets, :open
+
+    # add a column to keep track of the number of changes in a changeset.
+    # could probably work out how many changes there are here, but i'm not
+    # sure its actually important.
+    add_column(:changesets, :num_changes, :integer, 
+               :null => false, :default => 0)
+  end
+
+  def self.down
+    # in the reverse direction, we can look at the closed_at to figure out
+    # if changesets are closed or not.
+    add_column(:changesets, :open, :boolean, :null => false, :default => true)
+    execute("update changesets set open=(closed_at > now())")
+    remove_column :changesets, :closed_at
+
+    # remove the column for tracking number of changes
+    remove_column :changesets, :num_changes
+  end
+end