Add Rollback A Couple Migrations as a Rails TIL

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).
 
-_1457 TILs and counting..._
+_1458 TILs and counting..._
 
 ---
 
@@ -965,6 +965,7 @@ _1457 TILs and counting..._
 - [Rescue From With A Separate Method](rails/rescue-from-with-a-separate-method.md)
 - [Respond With JSON Regardless of Content Type](rails/respond-with-json-regardless-of-content-type.md)
 - [Retrieve An Object If It Exists](rails/retrieve-an-object-if-it-exists.md)
+- [Rollback A Couple Migrations](rails/rollback-a-couple-migrations.md)
 - [Rollback A Specific Migration Out Of Order](rails/rollback-a-specific-migration-out-of-order.md)
 - [Rounding Numbers With Precision](rails/rounding-numbers-with-precision.md)
 - [Run A Rake Task Programmatically](rails/run-a-rake-task-programmatically.md)

rails/rollback-a-couple-migrations.md

@@ -0,0 +1,25 @@
+# Rollback A Couple Migrations
+
+Let's say we need to rollback a couple Rails migrations that have been applied
+to our local environment. We run `rails db:migrate:status` and see that there
+are _2_ migrations that we want to _undo_.
+
+We can accomplish this by using the `STEP` env var with the rollback command.
+
+```bash
+$ rails db:rollback STEP=2
+```
+
+Just set `STEP` to the number of migrations that we need to rollback. If we
+then rerun `rails db:migrate:status` we'll now see those latest two migrations
+are `down`.
+
+Note: by default Rails doesn't like to operate with pending migrations. If we
+want to temporarily disable the pending migration check, we can alter the
+migration error config in `config/development.rb`.
+
+```diff
+  # Raise an error on page load if there are pending migrations.
+-  # config.active_record.migration_error = :page_load
++  config.active_record.migration_error = false
+```