activerecord/pg: support automatic timestamps in DDL

Updated (to show code)

I'd like to mimic ActiveRecord's automatic timestamps directly in the database, but without explicitly adding this logic after every migration's create_table() call.

Here's what I do now:

class开发者_开发知识库 StatusQuo < My::Migration::Subclass
  def self.up
    create_table :tbl do |t|
      ... some columns ...
      t.timestamps
    end
    add_default_now(:tbl, :created_at)  # ALTER COLUMN ... DEFAULT NOW()
    add_default_now(:tbl, :updated_at)  # ALTER COLUMN ... DEFAULT NOW()
    add_updated_at_trigger(:tbl)        # BEFORE UPDATE ON ... trg_updated_at()
  end
end

By contrast, here's what I'd like to do:

class Druthers < My::Migration::Subclass
  def self.up
    create_table :tbl do |t|
      ... some columns ...
      t.timestamps
    end
  end
end

Is there an easy or recommended way to accomplish this? Using activerecord 3, postgresql 8.4.

Here's the best I could come up with so far, full source here:

In config/environment.rb check to see if our connection adapter is PostgreSQL. If so, require a file that does the following:

1. Wrap ColumnDefinition#to_sql to force defaults

   Force "created_at" and "updated_at" to have DEFAULT CURRENT_TIMESTAMP

2. Wrap create_table to conditionally apply the trigger

   If the newly created table has an "updated_at" column, install a trigger referencing a database FUNCTION assumed to exist.

Not pretty (need to have maintain a FUNCTION definition outside of this code) and not complete (change_table won't handle introducing timestamps properly), but good enough.