From d8dfcce0fcc79a78dfbfd8ca21618080a1192159 Mon Sep 17 00:00:00 2001
From: jbranchaud <jbranchaud@gmail.com>
Date: Wed, 30 Apr 2025 23:18:32 -0500
Subject: [PATCH] Add Format DateTime With Builtin Formats as a Rails TIL

---
 README.md                                     |  3 +-
 rails/format-datetime-with-builtin-formats.md | 49 +++++++++++++++++++
 2 files changed, 51 insertions(+), 1 deletion(-)
 create mode 100644 rails/format-datetime-with-builtin-formats.md

diff --git a/README.md b/README.md
index 7731fd0..25f13a2 100644
--- a/README.md
+++ b/README.md
@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://crafty-builder-6996.ck.page/e169c61186).
 
-_1641 TILs and counting..._
+_1642 TILs and counting..._
 
 See some of the other learning resources I work on:
 - [Get Started with Vimium](https://egghead.io/courses/get-started-with-vimium~3t5f7)
@@ -1048,6 +1048,7 @@ If you've learned something here, support my efforts writing daily TILs by
 - [Find Or Create A Record With FactoryBot](rails/find-or-create-a-record-with-factory-bot.md)
 - [Find Records With Multiple Associated Records](rails/find-records-with-multiple-associated-records.md)
 - [Force All Users To Sign Out](rails/force-all-users-to-sign-out.md)
+- [Format DateTime With Builtin Formats](rails/format-datetime-with-builtin-formats.md)
 - [Generate A Model](rails/generate-a-model.md)
 - [Generate A Rails App From The Main Branch](rails/generate-a-rails-app-from-the-main-branch.md)
 - [Generating And Executing SQL](rails/generating-and-executing-sql.md)
diff --git a/rails/format-datetime-with-builtin-formats.md b/rails/format-datetime-with-builtin-formats.md
new file mode 100644
index 0000000..b2940eb
--- /dev/null
+++ b/rails/format-datetime-with-builtin-formats.md
@@ -0,0 +1,49 @@
+# Format DateTime With Builtin Formats
+
+The Rails [`Date`](https://api.rubyonrails.org/classes/Date.html)/`DateTime`
+and [`Time`](https://api.rubyonrails.org/classes/Time.html) classes each come
+with a `DATE_FORMATS` constant that is a hash of symbol names to format
+strings.
+
+```ruby
+> DateTime::DATE_FORMATS
+=>
+{:short=>"%d %b",
+ :long=>"%B %d, %Y",
+ :db=>"%Y-%m-%d",
+ :inspect=>"%Y-%m-%d",
+ :number=>"%Y%m%d",
+ :long_ordinal=>
+  #<Proc:0x0000000105b2cef0 /Users/jbranchaud/.local/share/mise/installs/ruby/3.2.2/lib/ruby/gems/3.2.0/gems/activesupport-8.0.1/lib/active_support/core_ext/date/conversions.rb:15 (lambda)>,
+ :rfc822=>"%d %b %Y",
+ :rfc2822=>"%d %b %Y",
+ :iso8601=>
+  #<Proc:0x0000000105b2cec8 /Users/jbranchaud/.local/share/mise/installs/ruby/3.2.2/lib/ruby/gems/3.2.0/gems/activesupport-8.0.1/lib/active_support/core_ext/date/conversions.rb:21 (lambda)>}
+```
+
+These can be used as a standardized, ready-to-use, named formats when turning
+`DateTime` objects into strings.
+
+Here are a few examples
+
+```ruby
+> now = DateTime.now
+=> Wed, 30 Apr 2025 23:08:08 -0500
+
+> now.to_fs(:long)
+=> "April 30, 2025 23:08"
+
+> now.to_fs(:long_ordinal)
+=> "April 30th, 2025 23:08"
+
+> now.to_fs(:iso8601)
+=> "2025-04-30T23:08:08-05:00"
+```
+
+If an unrecognized key is passed to `#to_fs`, then it falls back to the
+`:iso8601` format.
+
+```ruby
+> now.to_fs(:taco_bell)
+=> "2025-04-30T23:08:08-05:00"
+```