Add support for a NOT predicate

lib/arel/algebra/attributes/attribute.rb

@@ -86,6 +86,10 @@ module Arel
         Predicates::Equality.new(self, other)
       end
 
+      def not(other)
+        Predicates::Not.new(self, other)
+      end
+
       def lt(other)
         Predicates::LessThan.new(self, other)
       end

lib/arel/algebra/predicates.rb

@@ -33,6 +33,7 @@ module Arel
       end
     end
 
+    class Not                   < Binary; end
     class GreaterThanOrEqualTo  < Binary; end
     class GreaterThan           < Binary; end
     class LessThanOrEqualTo     < Binary; end

lib/arel/engines/memory/predicates.rb

@@ -10,6 +10,12 @@ module Arel
       def operator; :== end
     end
 
+    class Not < Binary
+      def eval(row)
+        operand1.eval(row) != operand2.eval(row)
+      end
+    end
+
     class GreaterThanOrEqualTo < Binary
       def operator; :>= end
     end

lib/arel/engines/sql/predicates.rb

@@ -26,6 +26,10 @@ module Arel
       end
     end
 
+    class Not < Binary
+      def predicate_sql; '!=' end
+    end
+
     class GreaterThanOrEqualTo < Binary
       def predicate_sql; '>=' end
     end

spec/algebra/integration/basic_spec.rb

@@ -49,6 +49,39 @@ share_examples_for 'A Relation' do
       expected = @expected.select { |r| r[@relation[:age]] == @pivot[@relation[:age]] }
       @relation.where(@relation[:age].eq(@pivot[@relation[:age]])).should have_rows(expected)
     end
+
+    it "finds rows with a not predicate" do
+      expected = @expected.select { |r| r[@relation[:age]] != @pivot[@relation[:age]] }
+      @relation.where(@relation[:age].not(@pivot[@relation[:age]])).should have_rows(expected)
+    end
+
+    it "finds rows with a less than predicate" do
+      expected = @expected.select { |r| r[@relation[:age]] < @pivot[@relation[:age]] }
+      @relation.where(@relation[:age].lt(@pivot[@relation[:age]])).should have_rows(expected)
+    end
+
+    it "finds rows with a less than or equal to predicate" do
+      expected = @expected.select { |r| r[@relation[:age]] <= @pivot[@relation[:age]] }
+      @relation.where(@relation[:age].lteq(@pivot[@relation[:age]])).should have_rows(expected)
+    end
+
+    it "finds rows with a greater than predicate" do
+      expected = @expected.select { |r| r[@relation[:age]] > @pivot[@relation[:age]] }
+      @relation.where(@relation[:age].gt(@pivot[@relation[:age]])).should have_rows(expected)
+    end
+
+    it "finds rows with a greater than or equal to predicate" do
+      expected = @expected.select { |r| r[@relation[:age]] >= @pivot[@relation[:age]] }
+      @relation.where(@relation[:age].gteq(@pivot[@relation[:age]])).should have_rows(expected)
+    end
+
+    it "finds rows with a matches predicate"
+
+    it "finds rows with an in predicate" do
+      pending
+      set = @expected[1..(@expected.length/2+1)]
+      @relation.all(:id.in => set.map { |r| r.id }).should have_resources(set)
+    end
   end
 end