Merge branch 'girishso-belongs_to_primary_key_doc'
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409460e440
@ -829,6 +829,7 @@ The `belongs_to` association supports these options:
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* `:counter_cache`
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* `:dependent`
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* `:foreign_key`
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* `:primary_key`
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* `:inverse_of`
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* `:polymorphic`
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* `:touch`
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@ -913,6 +914,25 @@ end
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TIP: In any case, Rails will not create foreign key columns for you. You need to explicitly define them as part of your migrations.
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##### `:primary_key`
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By convention, Rails assumes that the `id` column is used to hold the primary key of it's table.
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The `:primary_key` option allows you to specify a different column.
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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:
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```ruby
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class User < ActiveRecord::Base
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self.primay_key = 'guid' # primary key is guid and not id
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end
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class Todo < ActiveRecord::Base
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belongs_to :user, primary_key: 'guid'
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end
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```
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When we execute `@user.todos.create` then the `@todo` record will have `user_id` value as the `guid` value of `@user`.
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##### `:inverse_of`
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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.
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