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Building has_one from has_many Associations Discussion

Great tip! I use something similar for designating the thumbnail-image of a gallery of images. Something along these lines:

class Gallery
  has_many :images
  has_one :thumbnail, -> { where(thumbnail: true) }, class_name: "Image"
end

One of the benefits over this approach versus having a regular thumbnail method, is that you can eager-load the thumbnails and prevent N+1 problems using @galleries = Gallery.includes(:thumbnail)

If you need more flexibility, I think you can also use DelegatedTypes. For example if ShippingAddress needs a specific attribute or logic that BillingAddress doesn't need.

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And since the enum has created scopes for billing and shipping, you can DRY those associations up a little with:

has_one :billing_address,  -> { merge(Address.billing) }, class_name: "Address"
has_one :shipping_address, -> { merge(Address.shipping) }, class_name: "Address"
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Since the target of merge is already an Address collection, you can even use the scope methods directly:

has_one :billing_address,  -> { billing },  class_name: :Address
has_one :shipping_address, -> { shipping }, class_name: :Address
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Super nice!

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yeah, I wondered why he didn't just put billing and shipping in the scopes... glad to know that the scopes work normally from this context

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Thanks for the video!

Don't forget to also add unique constraints at the database level to make sure an Account can only have one shipping and one billing address.

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thanks, i keep wondering how to avoid incorrect get first billing / address

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Thanks all for contributing to the conversation! I've added a link to a blog post in the episode notes about this topic and included some things around validating uniqueness.

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