Add Model.pluck method like ActiveRecord: http://api.rubyonrails.org/…

…classes/ActiveRecord/Calculations.html#method-i-pluck

lib/mongoid/finders.rb

@@ -129,6 +129,17 @@ def first
     def last
       with_default_scope.last
     end
+
+    # Pick up values array by a column
+    #
+    # @example Pick up all email from User model
+    #   User.pluck(:email)
+    #
+    # @return [ Array ] The all values in column
+    def pluck(column_name)
+      column_name = column_name.to_sym
+      with_default_scope.all.only([column_name]).map(&column_name)
+    end
 
     protected
 
@@ -144,5 +155,6 @@ def last
     def find_or(method, attrs = {}, &block)
       where(attrs).first || send(method, attrs, &block)
     end
+
   end
 end

spec/mongoid/finders_spec.rb

@@ -428,6 +428,31 @@
       end
     end
   end
+
+
+  describe "#pluck" do    
+    it "work" do
+      Person.create(title: "Senorita")
+      Person.create(title: "Jason")
+      Person.pluck(:title).should eq(%w(Senorita Jason))
+    end
+
+    context "work with Criteria" do
+      before do
+        Person.create(title: "Senorita")
+        Person.create(title: "Jason", pets: true)
+        Person.create(title: "Tim")
+      end
+
+      it "with where" do
+        Person.where(pets: false).pluck(:title).should eq(%w(Senorita Tim))
+      end
+
+      it "with limit" do
+        Person.where(pets: false).limit(1).pluck(:title).should eq(%w(Senorita))
+      end
+    end
+  end
 
   Origin::Selectable.forwardables.each do |method|