Why did Rails 5 changed “index” to “foreign key”?

Question

If you had this in Rails 4:

t.references :event, index: true

Now you could use foreign_key instead of index in Rails

Answer 1

The index and foreign_key are different concepts, even if in Rails 5. So it's wrong to say the rails 5 changed “index” to “foreign key”.

The change from Rails 4 to Rails 5 is that the index option defaults to true, so you don't need to set it explicitly.

Method add_reference in rails 4.2.5

:index

Add an appropriate index. Defaults to false.

---

Method add_reference in rails 5.2

:index

Add an appropriate index. Defaults to true. See add_index for usage of this option.

That's why when you generate the references in rails 5 migration, you didn't see the index: true, because it's default.