I do not understand how to express the relationship between three separate tables

Question

Given the following tables in ActiveRecord:

• the authors
• Sites
• articles

I don’t know how to express that the author receives a different amount depending on the publication, but the authors working in the same publication have different rates:

• John publishes an article in Foo for $ 300
• John publishes an article in Bar for $ 350
• John publishes an article in the Base for $ 400.
• Dick publishes $ 250 Foo article
• Dick publishes an article in Bar for $ 400

and etc.

What connection am I trying to describe?

At the moment, I have a table of "bids" with author _id, site_id columns and quantity. Given publish.id and author.id, I get the article value using

cost = Rate.find(:first, :conditions => ["author_id = ? and site_id = ?", author.id, site.id]).rate

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Answer 1

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class Author
  has_many :publications, :through => :rates
end

class Publication
  has_many :authors, :through => :rates
end

class Rate #rich join table
  belongs_to :author
  belongs_to :publication
end

:

@author.rates.find_by_site_id(123)

,

@author.publications
@publication.authors

Answer 2

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Answer 3

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PK AuthorID.
PK PublicationID.
PK ArticleID.

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AuthorID (FK), PublicationID (FK), AtricleID (FK), , .

PK (AuthorID, PublicationID, ArticleID)

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Answer 4

:

author_site_mapper
------------------
id
author_id
site_id
rate

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