MONGOID-5910 Implement enumerable methods on top level models (any?, many?, and one?)

lib/mongoid/findable.rb

@@ -116,6 +116,36 @@ def exists?(id_or_conditions = :none)
       with_default_scope.exists?(id_or_conditions)
     end
 
+    # Return true if any documents exist in the criteria.
+    #
+    # @example Determine if any documents exist
+    #   Model.any?
+    #   
+    # @return [ true | false ] If any documents exist.
+    def any?()
+      limit(1).count > 0
+    end
+
+    # Return true if only one document exists in the criteria.
+    #
+    # @example Determine if only one document exists
+    #   Model.one?
+    #
+    # @return [ true | false ] If only one document exists.
+    def one?()
+      limit(2).count == 1
+    end
+
+    # Return true if more than one document exists in the criteria.
+    #
+    # @example Determine if many documents exist
+    #   Model.many?
+    #
+    # @return [ true | false ] If many documents exist.
+    def many?()
+      limit(2).count > 1
+    end
+
     # Finds a +Document+ or multiple documents by their _id values.
     #
     # If a single non-Array argument is given, this argument is interpreted

spec/mongoid/findable_spec.rb

@@ -160,6 +160,84 @@
     end
   end
 
+  describe "#any?" do
+    context "when called on collection with documents" do
+      before do
+        Band.create!(name: "Tool")
+      end
+
+      it "returns true" do
+        expect(Band.any?).to be true
+      end
+    end
+
+    context "when called on collection with no documents" do
+
+      it "returns false" do
+        expect(Band.any?).to be false
+      end
+    end
+  end
+
+  describe "#one?" do
+    context "when called on collection with no documents" do
+      it "returns false" do
+        expect(Band.one?).to be false
+      end
+    end
+
+    context "when called on collection with one document" do
+      before do
+        Band.create!(name: "Radiohead")
+      end
+
+      it "returns true" do
+        expect(Band.one?).to be true
+      end
+    end
+
+    context "when called on collection with multiple documents" do
+      before do
+        Band.create!(name: "Tool")
+        Band.create!(name: "Radiohead")
+      end
+
+      it "returns false" do
+        expect(Band.one?).to be false
+      end
+    end
+
+  end
+
+  describe "#many?" do
+    context "when called on collection with no documents" do
+      it "returns false" do
+        expect(Band.many?).to be false
+      end
+    end
+
+    context "when called on collection with one document" do
+      before do
+        Band.create!(name: "Radiohead")
+      end
+
+      it "returns false" do
+        expect(Band.many?).to be false
+      end
+    end
+
+    context "when called on collection with multiple documents" do
+      before do
+        Band.create!(name: "Radiohead")
+        Band.create!(name: "Tool")
+      end
+
+      it "returns true" do
+        expect(Band.many?).to be true
+      end
+    end
+  end
+
   describe "find_by!" do
 
     context "when the document is found" do