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In a RoR migration, how do I auto increment a non-primary-key field? I'd like to do this in the db definition, and not in the model.
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There can be only one AUTO_INCREMENT column per table, it must be indexed, and it cannot have a DEFAULT value. So you can indeed have an AUTO_INCREMENT column in a table that is not the primary key.
A Primary Key just needs to be a unique value that identifies its entry from other entries, and not null. Save this answer. Show activity on this post. Primary key should be unique but not necessarily need to be auto_increment.
AutoIncrement fields are integer in mysql. You can mirror the auto-increment field in a varchar field and create a trigger which updates the varchar field on insert/update.
No. A primary key must be unique and that has to be 100% guaranteed, and NON NULL A primary key should be stable if ever possible and not change. So you don't have to, but it's a good choice since there is no other naturally unique data and you don't want to have enormous primary keys.
You need to execute an SQL statement.
statement = "ALTER TABLE `users` CHANGE `id` `id` SMALLINT( 5 ) UNSIGNED NOT NULL AUTO_INCREMENT"
ActiveRecord::Base.connection.execute(statement)
you can entry manually in your migration
Note this is just an example. The final SQL statement syntax depends on the database.
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