I have a polymorphic association as follows
class Attachment < ActiveRecord::Base
belongs_to :attachable, polymorphic: true
has_attached_file :file
end
Then on my user model
class User < ActiveRecord::Base
has_many :attachments, as: :attachable
The I want to be able to do the following
attachment = Attachment.create(:file => params[:attachment])
attachment.user = current_user
But I am getting a
*** NoMethodError Exception: undefined method `user=' for #<Attachment:0x007fee92901ce8>
The attachment belongs to a attachable (which is polymorphic). The proper way to set this is to do so:
attachment.attachable = current_user
I strongly recommend you to rename your relationship to the following:
class Attachment < ActiveRecord::Base
belongs_to :owner, polymorphic: true
class User < ActiveRecord::Base
has_many :attachments, as: :owner
Because the relationship's name owner is way more explicit than attachable. See for yourself:
# What is easier to understan?
attachment.attachable = current_user
# or
attachment.owner = current_user
You can't reference a polymorphic relation that way. It'd have to be
attachment.attachable = current_user
Related
I have a User model that can have an email and a phone number, both of which are models of their own as they both require some form of verification.
So what I'm trying to do is attach Verification::EmailVerification as email_verifications and Verification::PhoneVerification as phone_verifications, which are both STIs of Verification.
class User < ApplicationRecord
has_many :email_verifications, as: :initiator, dependent: :destroy
has_many :phone_verifications, as: :initiator, dependent: :destroy
attr_accessor :email, :phone
def email
#email = email_verifications.last&.email
end
def email=(email)
email_verifications.new(email: email)
#email = email
end
def phone
#phone = phone_verifications.last&.phone
end
def phone=(phone)
phone_verifications.new(phone: phone)
#phone = phone
end
end
class Verification < ApplicationRecord
belongs_to :initiator, polymorphic: true
end
class Verification::EmailVerification < Verification
alias_attribute :email, :information
end
class Verification::PhoneVerification < Verification
alias_attribute :phone, :information
end
However, with the above setup I get the error uninitialized constant User::EmailVerification. I'm unsure of where I'm going wrong.
How I structure this so that I can access email_verifications and phone_verifications on the User model?
When using STI you don't need (or want) polymorphic associations.
Polymorphic associations are a hack around the object-relational impedance mismatch problem used to setup a single association that points to multiple tables. For example:
class Video
has_many :comments, as: :commentable
end
class Post
has_many :comments, as: :commentable
end
class Comment
belongs_to :commentable, polymorphic: true
end
The reason they should be used sparingly is that there is no referential integrity and there are numerous problems related to joining and eager loading records which STI does not have since you have a "real" foreign key column pointing to a single table.
STI in Rails just uses the fact that ActiveRecord reads the type column to see which class to instantiate when loading records which is also used for polymorphic associations. Otherwise it has nothing to do with polymorphism.
When you setup an association to a STI model you just have to create an association to the base inheritance class and rails will handle resolving the types by reading the type column when it loads the associated records:
class User < ApplicationRecord
has_many :verifications
end
class Verification < ApplicationRecord
belongs_to :user
end
module Verifications
class EmailVerification < ::Verification
alias_attribute :email, :information
end
end
module Verifications
class PhoneVerification < ::Verification
alias_attribute :email, :information
end
end
You should also nest your model in modules and not classes. This is partially due to a bug in module lookup that was not resolved until Ruby 2.5 and also due to convention.
If you then want to create more specific associations to the subtypes of Verification you can do it by:
class User < ApplicationRecord
has_many :verifications
has_many :email_verifications, ->{ where(type: 'Verifications::EmailVerification') },
class_name: 'Verifications::EmailVerification'
has_many :phone_verifications, ->{ where(type: 'Verifications::PhoneVerification') },
class_name: 'Verifications::PhoneVerification'
end
If you want to alias the association user and call it initiator you do it by providing the class name option to the belongs_to association and specifying the foreign key in the has_many associations:
class Verification < ApplicationRecord
belongs_to :initiator, class_name: 'User'
end
class User < ApplicationRecord
has_many :verifications, foreign_key: 'initiator_id'
has_many :email_verifications, ->{ where(type: 'Verifications::EmailVerification') },
class_name: 'Verifications::EmailVerification',
foreign_key: 'initiator_id'
has_many :phone_verifications, ->{ where(type: 'Verifications::PhoneVerification') },
class_name: 'Verifications::PhoneVerification',
foreign_key: 'initiator_id'
end
This has nothing to do with polymorphism though.
I'm using Rails 4.
I have an Anomaly Records class called Ar that inherits from the following classes as follows:
class RecordBase < ActiveRecord::Base
self.abstract_class = true
end
class ArAndEcrBase < RecordBase
self.abstract_class = true
# Relations
belongs_to :originator, class_name: 'User', foreign_key: 'originator_id'
has_many :attachments
end
class Ar < ArAndEcrBase
end
I want to share some relations with a class that handles another type of records in the Ar subclass however the has_many relationship doesn't work.
The following works:
> Ar.last.originator
=> #<User id: 1, ...
The following crashes:
> Ar.last.attachments
Mysql2::Error: Unknown column 'attachments.ar_and_ecr_base_id'
For some reason the has_many relationship doesn't work well. It should look for column attachments.ar_id and not attachments.ar_and_ecr_base_id
Am I doing something wrong? Or is this a Rails bug?
Atm the only way to get the code working is to move the has_many relation to the Ar class:
class Ar < ArAndEcrBase
has_many :attachments
end
If you want several models to have association to the same other model you probably need a polymorphic association
class Picture < ActiveRecord::Base
belongs_to :imageable, polymorphic: true
end
class Employee < ActiveRecord::Base
has_many :pictures, as: :imageable
end
class Product < ActiveRecord::Base
has_many :pictures, as: :imageable
end
I have a site that allows users to log in via multiple services (LinkedIn, Email, Twitter, etc..).
I have the below structure set up to model a User and their multiple identities. Basically a user can have multiple identieis, but only one of a given type (e.g. can't have 2 Twitter identiteis).
I decided to set it up as a polymorphic relationship, as drawn below. Basically there's a middle table identities that maps a User entry to multiple *_identity tables.
The associations are as follows (shown only for LinkedInIdentity, but can be extrapolated)
# /app/models/user.rb
class User < ActiveRecord::Base
has_many :identities
has_one :linkedin_identity, through: :identity, source: :identity, source_type: "LinkedinIdentity"
...
end
# /app/models/identity
class Identity < ActiveRecord::Base
belongs_to :user
belongs_to :identity, polymorphic: true
...
end
# /app/models/linkedin_identity.rb
class LinkedinIdentity < ActiveRecord::Base
has_one :identity, as: :identity
has_one :user, through: :identity
...
end
The problem I'm running into is with the User model. Since it can have multiple identities, I use has_many :identities. However, for a given identity type (e.g. LinkedIn), I used has_one :linkedin_identity ....
The problem is that the has_one statement is through: :identity, and there's no singular association called :identity. There's only a plural :identities
> User.first.linkedin_identity
ActiveRecord::HasManyThroughAssociationNotFoundError: Could not find the association :identity in model User
Any way around this?
I would do it like so - i've changed the relationship name between Identity and the others to external_identity, since saying identity.identity is just confusing, especially when you don't get an Identity record back. I'd also put a uniqueness validation on Identity, which will prevent the creation of a second identity of the same type for any user.
class User < ActiveRecord::Base
has_many :identities
has_one :linkedin_identity, through: :identity, source: :identity, source_type: "LinkedinIdentity"
end
# /app/models/identity
class Identity < ActiveRecord::Base
#fields: user_id, external_identity_id
belongs_to :user
belongs_to :external_identity, polymorphic: true
validates_uniqueness_of :external_identity_type, :scope => :user_id
...
end
# /app/models/linkedin_identity.rb
class LinkedinIdentity < ActiveRecord::Base
# Force the table name to be singular
self.table_name = "linkedin_identity"
has_one :identity
has_one :user, through: :identity
...
end
EDIT - rather than make the association for linkedin_identity, you could always just have a getter and setter method.
#User
def linkedin_identity
(identity = self.identities.where(external_identity_type: "LinkedinIdentity").includes(:external_identity)) && identity.external_identity
end
def linkedin_identity_id
(li = self.linkedin_identity) && li.id
end
def linkedin_identity=(linkedin_identity)
self.identities.build(external_identity: linkedin_identity)
end
def linkedin_identity_id=(li_id)
self.identities.build(external_identity_id: li_id)
end
EDIT2 - refactored the above to be more form-friendly: you can use the linkedin_identity_id= method as a "virtual attribute", eg if you have a form field like "user[linkedin_identity_id]", with the id of a LinkedinIdentity, you can then do #user.update_attributes(params[:user]) in the controller in the usual way.
Here is an idea that has worked wonderfully over here for such as case. (My case is a tad diffferent since all identites are in the same table, subclasses of the same base type).
class EmailIdentity < ActiveRecord::Base
def self.unique_for_user
false
end
def self.to_relation
'emails'
end
end
class LinkedinIdentity < ActiveRecord::Base
def self.unique_for_user
true
end
def self.to_relation
'linkedin'
end
end
class User < ActiveRecord::Base
has_many :identities do
[LinkedinIdentity EmailIdentity].each do |klass|
define_method klass.to_relation do
res = proxy_association.select{ |identity| identity.is_a? klass }
res = res.first if klass.unique_for_user
res
end
end
end
end
You can then
#user.identities.emails
#user.identities.linkedin
We've got 2 models & a join model:
#app/models/message.rb
Class Message < ActiveRecord::Base
has_many :image_messages
has_many :images, through: :image_messages
end
#app/models/image.rb
Class Image < ActiveRecord::Base
has_many :image_messages
has_many :messages, through: :image_messages
end
#app/models/image_message.rb
Class ImageMessage < ActiveRecord::Base
belongs_to :image
belongs_to :message
end
Extra Attributes
We're looking to extract the extra attributes from the join model (ImageMessage) and have them accessible in the Message model:
#message.image_messages.first.caption # -> what happens now
#message.images.first.caption #-> we want
We've already achieved this using the select method when declaring the association:
#app/models/message.rb
has_many :images, -> { select("#{Image.table_name}.*", "#{ImageMessage.table_name}.caption AS caption") }, class_name: 'Image', through: :image_messages, dependent: :destroy
Delegate
We've just found the delegate method, which does exactly what this needs. However, it only seems to work for has_one and belongs_to associations
We just got this working with a single association, but it seems it does not work for collections (just takes you to a public method)
Question
Do you know any way we could return the .caption attribute from the ImageMessage join model through the Image model?
We have this currently:
#app/models/image.rb
Class Message < ActiveRecord::Base
has_many :image_messages
has_many :messages, through: :image_messages
delegate :caption, to: :image_messages, allow_nil: true
end
#app/models/image_message.rb
Class ImageMessage < ActiveRecord::Base
belongs_to :image
belongs_to :message
def self.caption # -> only works with class method
#what do we put here?
end
end
Update
Thanks to Billy Chan (for the instance method idea), we have got it working very tentatively:
#app/models/image.rb
Class Image < ActiveRecord::Base
#Caption
def caption
self.image_messages.to_a
end
end
#app/views/messages/show.html.erb
<%= #message.images.each_with_index do |i, index| %>
<%= i.caption[index][:caption] %> #-> works, but super sketchy
<% end %>
Any way to refactor, specifically to get it so that each time .caption is called, it returns the image_message.caption value for that particular record?
delegate is just a shorthand as equivalent instance method. It's not a solution for all, and there are even some debate that it's not so explicit.
You can use an instance method when simple delegate can't fit.
I reviewed and found any association is unnecessary is this case. The ImageMessage's class method caption is more like a constant, you can refer it directly.
def image_message_caption
ImageMessage.caption
end
I've got a polymorphic association with a has_one and it gives me an error when trying to create through association.
class User < ActiveRecord::Base
belongs_to :userable, polymorphic: true
end
class Student < ActiveRecord::Base
attr_accessible :gender, :description, :dob
has_one :user, :as => :userable
end
If I try to do:
s = Student.new
s.user.create
I get and error Undefined method create for 'nil'
But! If i change the association to has_many users then I can now preform the same lines above.
Can anyone explain why this is happening? Thanks!
The problem is that user is nil since you haven't assigned a value to it.
You should use something like:
s.build_user(...)
or
s.create_user(...)