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| -rw-r--r-- | guides/source/association_basics.md | 19 |
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diff --git a/guides/source/association_basics.md b/guides/source/association_basics.md index ec6017ff73..b33e5d03f7 100644 --- a/guides/source/association_basics.md +++ b/guides/source/association_basics.md @@ -829,6 +829,7 @@ The `belongs_to` association supports these options: * `:counter_cache` * `:dependent` * `:foreign_key` +* `:primary_key` * `:inverse_of` * `:polymorphic` * `:touch` @@ -913,6 +914,24 @@ end TIP: In any case, Rails will not create foreign key columns for you. You need to explicitly define them as part of your migrations. +##### `:primary_key` + +By convention, Rails assumes that the column used to hold the primary key of it's table is `id`, and `:primary_key` allows you to specify a different column. + +Let's say that `users` table has `guid` as the primary key. And the requirement is that `todos` table should hold `guid` column value in the foreign key `user_id`. This can be achieved like this + +```ruby +class User < ActiveRecord::Base + self.primay_key = 'guid' # primary key is guid and not id +end + +class Todo < ActiveRecord::Base + belongs_to :user, primary_key: 'guid' +end +``` + +Now if we execute `@user.todos.create` then `@todo` record will have `user_id` value as the `guid` value of `@user`. + ##### `:inverse_of` The `:inverse_of` option specifies the name of the `has_many` or `has_one` association that is the inverse of this association. Does not work in combination with the `:polymorphic` options. |