Updated: ActiveRecord: Passing an empty array into NOT IN will return no records

Changes

-Be careful with the Active Record `where` method. When you accidentally pass an empty array to the `where` method using `NOT IN`, you probably will not get what you expected:
+Caution when using `.where` to exclude records from a scope like this:
+```rb
+# Fragile - avoid
+User.where("id NOT IN (?)", excluded_ids)
+```
+When the exclusion list is empty, you would expect this to return all records. However, this is not what happens:
```rb
-User.where("id NOT IN (?)", [])
+# Broken example
+User.where("id NOT IN (?)", []).to_sql
=>  SELECT `users`.* FROM `users` WHERE (id NOT IN (NULL))
```
-
-Even though you might expect this to return all records, this actually results none.
-
-**Never use the expression `id NOT IN (?)` without taking care of this case**! See below some workarounds.
+**Passing an empty exclusion list returns no records at all!** See below for better implementations.
+## Rails 4+
-## Rails >= 4
-
-If you use the same expression as above in Rails >= 4, it is still broken. But you can use the `.not` method to work around this issue.
+Use the `.not` method to let Rails do the logic
```rb
+# Good
User.where.not(id: []).to_sql 
=> SELECT "users".* FROM "users" WHERE (1=1)
User.where.not(id: [1]).to_sql
=> SELECT "users".* FROM "users" WHERE ("users"."id" != 1)
-puts User.where.not(id: [1, 2]).to_sql
+User.where.not(id: [1, 2]).to_sql
=> SELECT "users".* FROM "users" WHERE "users"."id" NOT IN (1, 2)
```
-
## Rails < 4
-Rails < 4 does not provide a pretty workaround.
-
+Before Rails 4, you needed to workaround this yourself:
```rb
-ids = []
-
-if ids.present?
- User.where("id NOT IN (?)", ids)
-else
-  User.all
-end
+# Good
+excluded_ids.blank? ? User.all : User.where("id NOT IN (?)", excluded_ids)
```