How to implement a unique index on two columns in rails

Ruby on-RailsActiverecord

Ruby on-Rails Problem Overview

I have a table and I'm trying to add a unique index on two columns. Those columns are also indexed. So my question is if I just can remove the indexes who were just for one column or if I have to use all three indexes:

add_index "subscriptions", ["user_id"]
add_index "subscriptions", ["content_id"]
add_index "subscriptions", ["user_id"], ["content_id"], :unique => true

Ruby on-Rails Solutions

Solution 1 - Ruby on-Rails

add_index :subscriptions, [:user_id, :content_id], unique: true
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