Add Manually Run A Migration From Rails Console as a rails til

Author: jbranchaud

README.md

@@ -9,7 +9,7 @@ and pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://tinyletter.com/jbranchaud).
 
-_902 TILs and counting..._
+_903 TILs and counting..._
 
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@@ -551,6 +551,7 @@ _902 TILs and counting..._
 - [Log SQL Queries Executed By ActiveRecord](rails/log-sql-queries-executed-by-activerecord.md)
 - [Mark A Migration As Irreversible](rails/mark-a-migration-as-irreversible.md)
 - [Make ActionMailer Synchronous In Test](rails/make-action-mailer-synchronous-in-test.md)
+- [Manually Run A Migration From Rails Console](rails/manually-run-a-migration-from-rails-console.md)
 - [Mark For Destruction](rails/mark-for-destruction.md)
 - [Merge A Scope Into An ActiveRecord Query](rails/merge-a-scope-into-an-activerecord-query.md)
 - [Migrating Up Down Up](rails/migrating-up-down-up.md)

rails/manually-run-a-migration-from-rails-console.md

@@ -0,0 +1,33 @@
+# Manually Run A Migrations From Rails Console
+
+A migration can be manually run from the rails console. In 99% of cases you are
+going to be better off using the migration CLI that Rails provides (e.g. `rails
+db:migrate`, `rails db:rollback`, etc.).
+
+If you are in a hyper-specific scenario where you need to run the `up` or the
+`down` of a migration without the migration-table check, then you'll want to
+consider this approach.
+
+First, connect to the rails console: `rails c`. Then require your migration
+file.
+
+```ruby
+> require "./db/migration/20200220181733_some_migration.rb"
+#=> true
+```
+
+You'll now have access to the `SomeMigration` constant. Create an instance of this and then run either the `up`-side of the migration:
+
+```ruby
+> SomeMigration.new.up
+#=> ... # a bunch of migration output
+```
+
+or the `down`-side of it:
+
+```ruby
+> SomeMigration.new.down
+#=> ... # a bunch of migration output
+```
+
+[source](https://stackoverflow.com/a/754316/535590)