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Diffstat (limited to 'guides/source')
| -rw-r--r-- | guides/source/association_basics.md | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/guides/source/association_basics.md b/guides/source/association_basics.md index ec6017ff73..d8dcf75740 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 +914,25 @@ 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 `id` column is used to hold the primary key of it's table. +The `:primary_key` option allows you to specify a different column. + +For example, given we have a `users` table with `guid` as the primary key. If we want a separate `todos` table to hold the foreign key `user_id` in the `guid` column, then we can use `primary_key` to achieve this like so: + +```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 +``` + +When we execute `@user.todos.create` then the `@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. |