How to Create a New Table With a Unique Index in an Active Record / Rails 4 Migration

Question

How do I create a new table, through a rails migration, and add an unique index to it?

In the docs I found how to add a index to a table after it\'s been created, but h

Answer 1

In Rails 5, you can provide index options along with column definition.

create_table :table_name do |t|
  t.string :key, null: false, index: {unique: true}
  t.jsonb :value

  t.timestamps
end


Column   |            Type             | Collation | Nullable |                 Default
------------+-----------------------------+-----------+----------+-----------------------------------------
id         | bigint                      |           | not null | nextval('table_name_id_seq'::regclass)
key        | character varying           |           | not null |
value      | jsonb                       |           |          |
created_at | timestamp without time zone |           | not null |
updated_at | timestamp without time zone |           | not null |
Indexes:
  "table_name_pkey" PRIMARY KEY, btree (id)
  "index_table_name_on_key" UNIQUE, btree (key)