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expanding on :uniq option in has_many

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1 parent 2f04c87 commit 44b752bea148b9df8f4d806e410e30fff26f680e Neeraj Singh committed Jul 9, 2010
@@ -889,7 +889,7 @@ module ClassMethods
# Specifies type of the source association used by <tt>has_many :through</tt> queries where the source
# association is a polymorphic +belongs_to+.
# [:uniq]
- # If true, duplicates will be omitted from the collection. Useful in conjunction with <tt>:through</tt>.
+ # If true, duplicates will be omitted from the collection. Works only in conjunction with <tt>:through</tt>.
# [:readonly]
# If true, all the associated objects are readonly through the association.
# [:validate]
@@ -1371,7 +1371,47 @@ The +:through+ option specifies a join model through which to perform the query.
h6(#has_many-uniq). +:uniq+
-Specify the +:uniq => true+ option to remove duplicates from the collection. This is most useful in conjunction with the +:through+ option.
+Specify the +:uniq => true+ option to remove duplicates from the collection. It only works with +:through+ option.
+
+<ruby>
+class Person < ActiveRecord::Base
+ has_many :readers
+ has_many :posts, :through => :readers
+
+ def self.lab
+ person = Person.create(:name => 'john')
+ p = Post.create(:name => 'a1')
+ person.posts << p
+ person.posts << p
+ person.reload
+ puts person.posts.inspect #=> [#<Post id: 5, name: "a1">, #<Post id: 5, name: "a1">]
+ puts Reader.all.inspect #=> [#<Reader id: 12, person_id: 5, post_id: 5>, #<Reader id: 13, person_id: 5, post_id: 5>]
+ end
+end
+</ruby>
+
+In the above case +readers+ table has two records and +person.posts+ brings out both of these records even though these records are basically pointing to the same +post+ record.
+
+Now let's add +uniq => true+ option.
+
+<ruby>
+class Person
+ has_many :readers
+ has_many :posts, :through => :readers, :uniq => true
+
+ def self.experiment
+ person = Person.create(:name => 'honda')
+ p = Post.create(:name => 'a1')
+ person.posts << p
+ person.posts << p
+ person.reload
+ puts person.posts.inspect #=> [#<Post id: 7, name: "a1">]
+ puts Reader.all.inspect #=> [#<Reader id: 16, person_id: 7, post_id: 7>, #<Reader id: 17, person_id: 7, post_id: 7>]
+ end
+end
+</ruby>
+
+In the above case +readers+ table still has two records. However +person.posts+ will show only one +post+ record because collection will load only +unique+ records.
h6(#has_many-validate). +:validate+

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