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PORight way to force uniqueness on a join model? (has_many :through)
 

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    <p>I have a parent/child relationship via our users table, with models as such:</p> <pre><code>class User &lt; ActiveRecord::Base # Parents relationship has_many :children_parents, :class_name =&gt; "ParentsChild", :foreign_key =&gt; "child_id", :dependent =&gt; :destroy has_many :parents, :through =&gt; :children_parents # Children relatiopnship has_many :parents_children, :class_name =&gt; "ParentsChild", :foreign_key =&gt; "parent_id", :dependent =&gt; :destroy has_many :children, :through =&gt; :parents_children ... end </code></pre> <p>And in parents_child.rb:</p> <pre><code>class ParentsChild &lt; ActiveRecord::Base belongs_to :parent, :class_name =&gt; "User" belongs_to :child, :class_name =&gt; "User" end </code></pre> <p>Right now, it is possible in our "add children" form (just using vanilla nested attributes) to add the same user as a child multiple times for parents. I am not sure what the 'right' way to go about forcing uniqueness in the ParentsChild relationship, although I am leaning towards a unique index on <code>(parent_id, child_id)</code> at the database layer (using a migration of course).</p> <p>I am sure I could also enforce uniqueness constraints in the UsersController::update method, but would prefer to avoid changing that code (right now it doesn't reference parents/children at all, thanks to nested attributes in the form/model) if possible. I am most concerned with making sure we use the "proper" solution. What is the 'right' or 'rails' way to do this?</p>
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    1. USBrett Bender
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