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POvalidate uniqueness amongst multiple subclasses with Single Table Inheritance
 

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  1. POvalidate uniqueness amongst multiple subclasses with Single Table Inheritance
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    <p>I have a Card model that has many CardSets and a CardSet model that has many Cards through a Membership model:</p> <pre><code>class Card &lt; ActiveRecord::Base has_many :memberships has_many :card_sets, :through =&gt; :memberships end class Membership &lt; ActiveRecord::Base belongs_to :card belongs_to :card_set validates_uniqueness_of :card_id, :scope =&gt; :card_set_id end class CardSet &lt; ActiveRecord::Base has_many :memberships has_many :cards, :through =&gt; :memberships validates_presence_of :cards end </code></pre> <p>I also have some sub-classes of the above using Single Table Inheritance:</p> <pre><code>class FooCard &lt; Card end class BarCard &lt; Card end </code></pre> <p>and</p> <pre><code>class Expansion &lt; CardSet end class GameSet &lt; CardSet validates_size_of :cards, :is =&gt; 10 end </code></pre> <p>All of the above is working as I intend. What I'm trying to figure out is how to validate that a Card can only belong to a single Expansion. I want the following to be invalid:</p> <pre><code>some_cards = FooCard.all( :limit =&gt; 25 ) first_expansion = Expansion.new second_expansion = Expansion.new first_expansion.cards = some_cards second_expansion.cards = some_cards first_expansion.save # Valid second_expansion.save # **Should be invalid** </code></pre> <p>However, GameSets should allow this behavior:</p> <pre><code>other_cards = FooCard.all( :limit =&gt; 10 ) first_set = GameSet.new second_set = GameSet.new first_set.cards = other_cards # Valid second_set.cards = other_cards # Also valid </code></pre> <p>I'm guessing that a validates_uniqueness_of call is needed somewhere, but I'm not sure where to put it. Any suggestions?</p> <h2>UPDATE 1</h2> <p>I modified the Expansion class as sugested:</p> <pre><code>class Expansion &lt; CardSet validate :validates_uniqueness_of_cards def validates_uniqueness_of_cards membership = Membership.find( :first, :include =&gt; :card_set, :conditions =&gt; [ "card_id IN (?) AND card_sets.type = ?", self.cards.map(&amp;:id), "Expansion" ] ) errors.add_to_base("a Card can only belong to a single Expansion") unless membership.nil? end end </code></pre> <p>This works! Thanks J.!</p> <h2>Update 2</h2> <p>I spoke a little too soon. The above solution was working great until I went to update an Expansion with a new card. It was incorrectly identifying subsequent <code>#valid?</code> checks as false because it was finding itself in the database. I fixed this by adding a check for <code>#new_record?</code> in the validation method:</p> <pre><code>class Expansion &lt; CardSet validate :validates_uniqueness_of_cards def validates_uniqueness_of_cards sql_string = "card_id IN (?) AND card_sets.type = ?" sql_params = [self.cards.map(&amp;:id), "Expansion"] unless new_record? sql_string &lt;&lt; " AND card_set_id &lt;&gt; ?" sql_params &lt;&lt; self.id end membership = Membership.find( :first, :include =&gt; :card_set, :conditions =&gt; [sql_string, *sql_params] ) errors.add_to_base("a Card can only belong to a single Expansion") unless membership.nil? end </code></pre>
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