Will removing a column with a Rails migration remove indexes associated with the column

Question

In Rails 2, will removing a column with a Rails migration also change/remove indexes associated with the column? If not, and instead you have to also change/remove each index manually, shouldn't it instead be automated?

Thanks (from a Rails newbie)

Foray

By the way here's an interesting post that does not necessarily directly answer my question however: keyj.wordpress.com/2009/05/28/… – Foray

Update: currently, it does remove the index (Rails 4.1.7). – Columba

Answer 1

No, unfortunately you have to remove the index manually from within your migration using the remove_index method.

Pandybat

for MySQL 5.1 (at least) this does not appear to be the case. See: stackoverflow.com/a/4341928 – Tamathatamaulipas

In Rails 4 it does now: https://mcmap.net/q/64467/-will-removing-a-column-with-a-rails-migration-remove-indexes-associated-with-the-column (e.g.: I tried and after remove_column ..., remove_index ... throws a "Index name '...' on table '...' does not exist" <3 ) – Bortman

Answer 2

From Rails 4 upwards, the index removes automatically with the column removal.

Interosculate

Although removing column will remove its index, it won't be fully reversible. Rollback will not add the index back. In this case remove_index is needed – Comeon

Answer 3

To clarify, inside a migration the syntax to remove a 2 column index is the following

remove_index :actions, :column => [:user_id,:action_name]

or by name, a worse option from my point of view

remove_index :actions, :name => "index_actions_on_user_id_and_action_name"

Mobley

remove_index by name is not reversible, so it's better to use column – Montes

Answer 4

Just as a caution, while Rails 4 will remove the index for you if you remove the column, you should specify the column type. Without a column type, running rake db:rollback will return

rake aborted!
StandardError: An error has occurred, all later migrations canceled:

remove_column is only reversible if given a type.

I was experimenting with dropping foreign key columns that were indexed. Even specifying index: true in the change block didn't seem to make the columns reversible on rollback.

Abdication

Answer 5

If you want to remove index you should use remove_index, if you use remove_column it does remove the index but you can't run rake db:rollback. As Jim mentioned.

remove_column is only reversible if given a type.

Leukoderma

Answer 6

In Rails > 3.2.16, removing the column removes the index.

Silicle