add_index is unnecessary and may cause errors

[jaeming]

I was checking out the related tutorial for this and found an error in the migration:

add_index :users, :token

This doesn't make sense as indexing foreign keys can only happen between two different tables. You would not index a column to a table to which it already belongs. In other words, you'd only do something like this if Token was a separate table.

If you switch your db to postgres you'll get an error while trying to migrate:

PG::UndefinedTable: ERROR:  relation "users" does not exist
: CREATE  INDEX  "index_users_on_token" ON "users"  ("token")

The reason it work in SQLite is because SQLite basically ignores foreign keys.

[bparanj]

Good catch! I will update the article and the code.