Merge pull request #5321 from pfeiffer/uniqueness_validator_conditions

Add :conditions option to uniqueness validator

activerecord/lib/active_record/validations/uniqueness.rb

@@ -35,8 +35,14 @@ def validate_each(record, attribute, value)
           relation = relation.and(table[scope_item].eq(scope_value))
         end
 
-        if finder_class.unscoped.where(relation).exists?
-          record.errors.add(attribute, :taken, options.except(:case_sensitive, :scope).merge(:value => value))
+        relation = finder_class.unscoped.where(relation)
+
+        if options[:conditions]
+          relation = relation.merge(options[:conditions])
+        end
+
+        if relation.exists?
+          record.errors.add(attribute, :taken, options.except(:case_sensitive, :scope, :conditions).merge(:value => value))
         end
       end
 
@@ -102,6 +108,14 @@ module ClassMethods
       #     validates_uniqueness_of :teacher_id, :scope => [:semester_id, :class_id]
       #   end
       #
+      # It is also possible to limit the uniqueness constraint to a set of records matching certain conditions.
+      # In this example archived articles are not being taken into consideration when validating uniqueness
+      # of the title attribute:
+      #
+      #   class Article < ActiveRecord::Base
+      #     validates_uniqueness_of :title, :conditions => where('status != ?', 'archived')
+      #   end
+      #
       # When the record is created, a check is performed to make sure that no record exists in the database
       # with the given value for the specified attribute (that maps to a column). When the record is updated,
       # the same check is made but disregarding the record itself.
@@ -109,6 +123,8 @@ module ClassMethods
       # Configuration options:
       # * <tt>:message</tt> - Specifies a custom error message (default is: "has already been taken").
       # * <tt>:scope</tt> - One or more columns by which to limit the scope of the uniqueness constraint.
+      # * <tt>:conditions</tt> - Specify the conditions to be included as a <tt>WHERE</tt> SQL fragment to limit
+      #   the uniqueness constraint lookup. (e.g. <tt>:conditions => where('status = ?', 'active')</tt>)
       # * <tt>:case_sensitive</tt> - Looks for an exact match. Ignored by non-text columns (+true+ by default).
       # * <tt>:allow_nil</tt> - If set to true, skips this validation if the attribute is +nil+ (default is +false+).
       # * <tt>:allow_blank</tt> - If set to true, skips this validation if the attribute is blank (default is +false+).

activerecord/test/cases/validations/uniqueness_validation_test.rb

@@ -325,4 +325,16 @@ def test_validate_straight_inheritance_uniqueness
     assert w6.errors[:city].any?, "Should have errors for city"
     assert_equal ["has already been taken"], w6.errors[:city], "Should have uniqueness message for city"
   end
+  
+  def test_validate_uniqueness_with_conditions
+    Topic.validates_uniqueness_of(:title, :conditions => Topic.where('approved = ?', true))
+    t1 = Topic.create("title" => "I'm a topic", "approved" => true)
+    t2 = Topic.create("title" => "I'm an unapproved topic", "approved" => false)
+    
+    t3 = Topic.new("title" => "I'm a topic", "approved" => true)
+    assert !t3.valid?, "t3 shouldn't be valid"
+    
+    t4 = Topic.new("title" => "I'm an unapproved topic", "approved" => false)
+    assert t4.valid?, "t4 should be valid"
+  end
 end