Question

When I was creating a model, I made a column edited:timestamp.

t.timestamp :edited # in migration file

Was expecting that whenever user edits anything in this model, the time/date will be updated.

But I just saw that in database schema it is written down as

t.datetime "edited"

and it expects user to enter data in a form.

What’s happening here?

How should I change my migration file to make a timestamp column in SQL DB? Or I should assign it in the model itself?

I don’t want it to depend on user input, has to be a system cell

thx.

Answer 1

When you create a model, you should then generate a ActiveRecord migration to create the table that will store the data associated with this model. For example, if your model is called ‘Product’, run:

rails g migration create_products_table

this will generate a migration file in db/migrate (prefixed with the timestamp at which you generated the migration file, eg: “20121201200720_create_products_table.rb”)

The migration file should look like this:

class CreateProducts < ActiveRecord::Migration
  def change
    create_table :products do |t|

      t.timestamps
    end
  end
end

When you run this migration (rake db:migrate), ActiveRecord will automatically create two columns in your table : created_at and updated_at. Then go and have a look at your schema.rb (in db). There will be something like that:

create_table "products", :force => true do |t|
    t.datetime "created_at", :null => false
    t.datetime "updated_at", :null => false
end

created_at will store the timestamp at which the product was created.
updated_at will store the timestamp at which the product was last updated (what you’re looking for here)

So you don’t have to create a custom column, you should just rely on ActiveRecord’s built-in timestamps.