I have a table design style, which has api_id field with unique key
CREATE TABLE `design_style` (
`id` bigint(20) NOT NULL AUTO_INCREMENT,
`api_id` varchar(5) COLLATE utf8_unicode_ci NOT NULL,
.....
PRIMARY KEY (`id`),
UNIQUE KEY `api_id` (`api_id`),
UNIQUE KEY `name` (`name`),
KEY `category_id_idx` (`category_id`),
CONSTRAINT `design_style_category_id_design_style_category_id` FOREIGN KEY (`category_id`) REFERENCES `design_style_category` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci

I reverse engineered the database tables and created entities. I am using it in symfony2 app.

Then I executed
php app/console doctrine:schema:update --dump-sql
and also checked with migrations diff
php app/console doctrine:migrations:diff

but has given me
DROP INDEX api_id ON design_page