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Editorial Team
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Asked: 2026-05-21T21:16:00+00:00

I have a migration that adds an index to an existing table using add_index

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I have a migration that adds an index to an existing table using add_index:

add_index :foo, [:foo_type, :bar_id, :baz_id], :unique => true

However, my fields are long enough that they exceed the maximum InnoDB key length. As per Anders Arpteg’s answer to How do I increase key length in MySQL 5.1?, I need to generate SQL like this:

CREATE UNIQUE INDEX `index_matches_on_foo_and_bar_id_and_baz_id` ON `matches` (`foo`(100), `bar_id`(100), `baz_id`(100))

Can I do this in a nice Rails-y way, or must I stoop to using raw SQL in my migration?

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1 Answer

  1. Editorial Team

    Unfortunately, rails do not support the :limit option in add_index (at least not in 2.x). However, you can always use execute instead and enter the sql directly.

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