How would I model has_many and also mark one of the 'many' as special?

Rails
1

I have an Image class with

belongs_to :attachable, :polymorphic => true

Titles can have Images, and so can People. In the Person class, I have
the apposite relationship:

has_many :images, :as => :attachable, :dependent => :destroy
accepts_nested_attributes_for :images, :reject_if => lambda { |a|
a[:file].blank? && a[:file_uid].blank? && a[:file_url].blank? &&
a[:name].blank? }, :allow_destroy => true

This all works fine, I’ve got my forms working perfectly. Now I would
like to mark one image as being the “portrait” for this person, and I’m
stuck on how best to do this. I have done it in the past in what I
recognize was a very hacky manner, just adding an image_id to the parent
class and setting that in my controller. I’d rather go with the flow.

How would you add this to the models so that the relationship can be
expressed in a normal nested form?

Walter

2

On Wed, Jan 16, 2013 at 4:09 PM, Walter Lee D. [email protected]
wrote:

I would like to mark one image as being the “portrait” for this person,

I’d suggest adding that a person has_one portrait, class_name: :Image.
In the UI you can have them select one of their Images (or none).

-Dave

–
Dave A., the T. Rex of Codosaurus LLC,
secret-cleared freelance software developer
taking contracts in or near NoVa or remote.
See information at http://www.Codosaur.us/.

3

On Jan 16, 2013, at 4:16 PM, Dave A. wrote:

On Wed, Jan 16, 2013 at 4:09 PM, Walter Lee D. [email protected] wrote:

I would like to mark one image as being the “portrait” for this person,

I’d suggest adding that a person has_one portrait, class_name: :Image.
In the UI you can have them select one of their Images (or none).

-Dave

Does that require me to add another belongs_to to the Image? If I add a
has_one, won’t I have to balance that on the other side?

Walter

4

On Jan 16, 2013, at 4:09 PM, Walter Lee D. wrote:

How would you add this to the models so that the relationship can be expressed
in a normal nested form?

Walter

I made a little dummy app to test this out in console, and got the
following to work, but (maybe it’s just me) the naming seems wrong:

class Person < ActiveRecord::Base
attr_accessible :photo, :name
has_many :photos, :as => :attachment, :dependent => :destroy
belongs_to :photo
end

class Photo < ActiveRecord::Base
attr_accessible :file_name, :name
belongs_to :attachment, :polymorphic => true
has_one :person
end

Ignore the fact that I called it Photo rather than Image in this one…

Photo has_one person, but there are going to be instances where the
attachment is to a Title (which doesn’t need that relationship), and I’m
not sure what happens then.

Walter

5

class Person < ActiveRecord::Base
attr_accessible :photo, :name
has_many :photos, :as => :attachment, :dependent => :destroy

I would do this. This will save a portrait_id on a person object,

which is the id of a photo. This is most efficient because if you put
the
“belongs_to” association on the photo object, you’ll end up with many
photos with nil values for person_id.
belongs_to :portrait, :class_name => “Photo”
end

class Photo < ActiveRecord::Base
attr_accessible :file_name, :name
belongs_to :attachment, :polymorphic => true
end

6

On Jan 17, 2013, at 11:30 AM, Emily S wrote:

belongs_to :attachment, :polymorphic => true
Thanks for the suggestion. Would I also need to add anything to the
Photo class to hold up the other side of the belongs_to? has_one
:person, maybe? Or would it work without that?

Walter

7

On Jan 16, 2013, at 4:23 PM, Walter Lee D. wrote:

-Dave

Does that require me to add another belongs_to to the Image? If I add a has_one,
won’t I have to balance that on the other side?

Walter

Just tried this in my stunt app, and it would require me to add a
person_id to the Photo / Image model, which since it’s polymorphic, is
sort of beside the point.

Walter