Rails type database field

Question

I have a table called Notification. This table has the following fields :id , :user_id , :foreign_id , :type

I want to associate Notifications with other tables like Friend , Quiz , Sport , Trip using the foreign key field :foreign_id, so that I can store different types of notifications in a generic way. I would like to store what type of notification in the :type database column such as "Friend" or "Quiz" and so on.

What is the best way to achieve something like this in Rails?

Art Shayderov · Accepted Answer · 2011-12-02 07:10:11Z

3

My guess is what you are looking for is called Polymorphic Associations

answered Dec 2, 2011 at 7:10

Art Shayderov

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KL-7 · Accepted Answer · 2011-12-02 07:05:43Z

1

You can store class name of the associated object as a string in object_type (or however you name it) field, that allows you to retrieve associated object like that:

# create new notification for quiz
Notification.create(user_id: user.id, foreign_id: quiz.id, object_type: quiz.class.to_s)

# load associated object for notification
associated_object = notification.object_type.constantize.find(notification.foreign_id)

answered Dec 2, 2011 at 7:05

KL-7

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2 Comments

theReverseFlick Over a year ago

Are the column names :foreign_id , :object_type built-in conventions?

KL-7 Over a year ago

No, they aren't. In fact you'd better use Polymorphic Associations as Art Shayderov suggested. It will be a better solution. Approach I suggested is more robust and may be not as good in actual project. See this Railscast for nice explanation of polymorphic associations.

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