Add Set A Timestamp Field To The Current Time as a Rails til

Author: jbranchaud

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
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-_1018 TILs and counting..._
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@@ -668,6 +668,7 @@ _1018 TILs and counting..._
 - [Select A Select By Selector](rails/select-a-select-by-selector.md)
 - [Select Value For SQL Counts](rails/select-value-for-sql-counts.md)
 - [Serialize With fast_jsonapi In A Rails App](rails/serialize-with-fast-jsonapi-in-a-rails-app.md)
+- [Set A Timestamp Field To The Current Time](rails/set-a-timestamp-field-to-the-current-time.md)
 - [Set default_url_options For Entire Application](rails/set-default-url-options-for-entire-application.md)
 - [Set Schema Search Path](rails/set-schema-search-path.md)
 - [Show Pending Migrations](rails/show-pending-migrations.md)

rails/set-a-timestamp-field-to-the-current-time.md

@@ -0,0 +1,27 @@
+# Set A Timestamp Field To The Current Time
+
+To set a timestamp field to the current time, you could reach for the `#update`
+method like you would when modifying any other field.
+
+```ruby
+MagicLink
+  .find_by(token: some_token)
+  .update(used_at: Time.zone.now)
+```
+
+This works, but it's more verbose than is necessary and requires that you
+construct the right timestamp for _now_ (time zones and all).
+
+Rails has a more concise and idomatic way of doing this:
+[`#touch`](https://api.rubyonrails.org/v6.1.0/classes/ActiveRecord/Persistence.html#method-i-touch).
+
+```ruby
+MagicLink
+  .find_by(token: some_token)
+  .touch(:used_at)
+```
+
+Updating a timestamp to the current time is a common action in web
+applications, so Rails offers the `#touch` method as a shorthand for doing it.
+This will set the given field, in this case `:used_at`, to the current time.
+This will also set the `updated_at/on` field.