how to make column unique and index it in Rails Migration

Question

Hello,

I would like to make a column unique in Rails migration script. What is the best way to do it? Also is there a way to index a column in table?

I would like to enforce unique columns in database as opposed to just using :validate_uniqueness_of

Thanks,

Tam

Answer 1

The short answer:

add_index :table_name, :column_name, :unique => true

To index multiple columns together, you pass an array of column names instead of a single column name,

add_index :table_name, [:column_name_a, :column_name_b]

For finer grained control, there's a "execute" method that executes straight SQL.

That's it!

If you are doing this as a replacement for regular old model validations, just check to see how it works. I'm not sure the error reporting to the user will be as nice. You can always do both.

Answer 2

For solve problem of adding unique index after creating table you can use 1) rake:db migrate VERSION=0 2) rake:db migrate instead of rake db:setup