create an entry for validates_uniquessness_of if one does not exist

NEWS.md

@@ -3,6 +3,10 @@
 * Prefer Test::Unit to Minitest when loading integrations so that RubyMine is
   happy (#88).
 
+* `validates_uniqueness_of` will now create a record if one does not exist.
+  Previously, users were required to create a record in the database before
+  using this matcher.
+
 # v1.2.0
 
 * `ensure_inclusion_of` now has an `in_array` parameter:

README.md

@@ -30,12 +30,7 @@ Matchers to test validations and mass assignments:
       it { should validate_presence_of(:body).with_message(/wtf/) }
       it { should validate_presence_of(:title) }
       it { should validate_numericality_of(:user_id) }
-
-      # validates_uniqueness_of requires an entry to be in the database already
-      it "validates uniqueness of title" do
-        Post.create!(title: "My Awesome Post", body: "whatever")
-        should validate_uniqueness_of(:title)
-      end
+      it { should validate_uniqueness_of(:title) }
     end
 
     describe User do

lib/shoulda/matchers/active_model/validate_uniqueness_of_matcher.rb

@@ -68,20 +68,25 @@ module Shoulda # :nodoc:
         def matches?(subject)
           @subject = subject.class.new
           @expected_message ||= :taken
-          has_existing? &&
-            set_scoped_attributes &&
+          set_scoped_attributes &&
             validate_attribute? &&
             validate_after_scope_change?
         end
 
         private
 
-        def has_existing?
-          if @existing = @subject.class.find(:first)
-            true
-          else
-            @failure_message = "Can't find first #{class_name}"
-            false
+        def existing
+          @existing ||= first_instance
+        end
+
+        def first_instance
+          @subject.class.first || create_instance_in_database
+        end
+
+        def create_instance_in_database
+          @subject.class.new.tap do |instance|
+            instance.send("#{@attribute}=", "arbitrary_string")
+            instance.save(:validate => false)
           end
         end
 
@@ -90,7 +95,7 @@ module Shoulda # :nodoc:
             @options[:scopes].all? do |scope|
               setter = :"#{scope}="
               if @subject.respond_to?(setter)
-                @subject.send("#{scope}=", @existing.send(scope))
+                @subject.send("#{scope}=", existing.send(scope))
                 true
               else
                 @failure_message = "#{class_name} doesn't seem to have a #{scope} attribute."
@@ -114,7 +119,7 @@ module Shoulda # :nodoc:
             true
           else
             @options[:scopes].all? do |scope|
-              previous_value = @existing.send(scope)
+              previous_value = existing.send(scope)
 
               # Assume the scope is a foreign key if the field is nil
               previous_value ||= 0
@@ -144,7 +149,7 @@ module Shoulda # :nodoc:
         end
 
         def existing_value
-          value = @existing.send(@attribute)
+          value = existing.send(@attribute)
           if @options[:case_insensitive] && value.respond_to?(:swapcase!)
             value.swapcase!
           end

spec/shoulda/active_model/validate_uniqueness_of_matcher_spec.rb

@@ -34,13 +34,8 @@ describe Shoulda::Matchers::ActiveModel::ValidateUniquenessOfMatcher do
         @matcher = validate_uniqueness_of(:attr)
       end
 
-      it "should fail to require a unique value" do
-        @model.should_not @matcher
-      end
-
-      it "should alert the tester that an existing value is not present" do
-        @matcher.matches?(@model)
-        @matcher.negative_failure_message.should =~ /^Can't find first .*/
+      it "does not not require a created instance" do
+        @model.should @matcher
       end
     end
   end