Rails has_many :through with uniqueness - ruby-on-rails

Question

I asked this question differently, but deleted it to attempt more clarity.
I have an Article model. It has_many contacts, through: :article_contacts.
I have a Contact model. It has_many articles, through: :article_contacts.
What I need is each Contact object to be unique, but be able to be associated with different articles. My last question led to people showing me how to display only unique contacts, or to validate the join model, but that's not what I need.
I need, for example, tables like the following:
Article
id: 1, name: "Whatever", content: "Whatever"
id: 2, name: "Again, whatever", content: "Whateva"
Contact
id: 1, email: "email#email.com"
id: 2, email: "secondemail#email.com"
ArticleContact
id: 1, article_id: 1, contact_id: 1
id: 2, article_id: 1, contact_id: 2
id: 3, article_id: 2, contact_id: 1
So, when I build the association in my Article controller in the new action and I call #article.save in the create action, I get an insert of the new article, an insert of the contact and an insert of the article_relationship. Great.
BUT, on Article 2, if I add the same email to the contact form, I do not want to create another Contact with the same email. But I do want (as you see with the third ID in ArticleContact above) to create. But each call to #article.save does it. I've tried first_or_initialize and << into the collection, but it always creates multiple times and if I have a validation, it means I can't create the ArticleContact relationship because contact is unique.
I may eventually have a drop down with contacts, but I suspect that will be long, so I'd rather simply enter an email into a form and have the code check that it is unique and if so, just create the join relationship using the existing ID.
This must be easier than I am conceiving, but I can't find a single article that demonstrates this anywhere.
Updated with code per request, though, again, I don't have the code to only create a unique contact and associate the relationship with an existing one. That's what I'm missing so this code will only show you what I already know works and not how to get to what I want :).
articlecontroller:
def new
#article = #business.articles.build
authorize #business
#article.attachments.build
#article.contacts.build
end
def create
#article = #business.articles.new(article_params)
authorize #business
respond_to do |format|
if #article.save
format.html { redirect_to business_article_path(#business, #article), notice: "Knowledge created." }
else
format.html { render 'new' }
end
end
end
Models have the standard has_many :thruogh and belongs to. I can show it, but they are the right way. View is just a standard simple_form building the contact:
<%= f.simple_fields_for :contacts, class: "form-inline" do |contact| %>
<%= contact.input :first_name, label: "Contact First Name" %>
<%= contact.input :last_name, label: "Contact Last Name" %>
<%= contact.input :email, label: "Contact Email" %>
<% end %>

Answer 1

You should enforce uniqueness, just in case:
# contact.rb
class Contact
...
validates_uniqueness_of :email
...
end
But in your controller you could do:
# articles_controller.rb
def create
...
# we can rely on it's uniqueness
contacts << Contact.find_or_create_by(email: param[:email)
...
end
Or whatever best fits your needs.
Hope this helps!

Answer 2

give your ArticleContact a validation with a scope.
validates :article_id, unique {scope: :contact_id}
this will prevent you from having ArticleContacts that are exactly the same.
when you create a contact, try:
contact = Contact.where(email: "e#mail.com:").first_or_create
in contact.rb
validates :email, uniqueness: true

Answer 3

You could try this in the create method
verified_contacts = []
#article.contacts.each do |contact|
existing_contact = Contact.find_by(email: contact.email)
verified_contacts << (existing_contact || contact)
end
#article.contacts = verified_contacts