ObjectID#from_time RUBY-82

lib/mongo/types/objectid.rb

@@ -51,6 +51,22 @@ module Mongo
       str && str.length == len && match == str
     end
 
+    # Create an object id from the given time. This is useful for doing range
+    # queries; it works because MongoDB's object ids begin
+    # with a timestamp.
+    #
+    # @param [Time] time a utc time to encode as an object id.
+    #
+    # @return [Mongo::ObjectID]
+    #
+    # @example Return all document created before Jan 1, 2010.
+    #   time = Time.utc(2010, 1, 1)
+    #   time_id = ObjectID.from_time(time)
+    #   collection.find({'_id' => {'$lt' => time_id}})
+    def self.from_time(time)
+      self.new([time.to_i,0,0].pack("NNN").unpack("C12"))
+    end
+
     # Adds a primary key to the given document if needed.
     #
     # @param [Hash] doc a document requiring an _id.
@@ -163,7 +179,7 @@ module Mongo
     #
     # @return [Time] the time at which this object was created.
     def generation_time
-      Time.at(@data.pack("C4").unpack("N")[0])
+      Time.at(@data.pack("C4").unpack("N")[0]).utc
     end
 
     private

test/test_cursor.rb

@@ -123,6 +123,27 @@ class CursorTest < Test::Unit::TestCase
     assert_equal MaxKey.new, results[3]['n']
   end
 
+  def test_id_range_queries
+    @@coll.remove
+
+    t1 = Time.now
+    t1_id = ObjectID.from_time(t1)
+    @@coll.save({:t => 't1'})
+    @@coll.save({:t => 't1'})
+    @@coll.save({:t => 't1'})
+    sleep(2)
+    t2 = Time.now
+    t2_id = ObjectID.from_time(t2)
+    @@coll.save({:t => 't2'})
+    @@coll.save({:t => 't2'})
+    @@coll.save({:t => 't2'})
+
+    assert_equal 3, @@coll.find({'_id' => {'$gt' => t1_id}, '_id' => {'$lt' => t2_id}}).count
+    @@coll.find({'_id' => {'$gt' => t2_id}}).each do |doc|
+      assert_equal 't2', doc['t']
+    end
+  end
+
   def test_limit
     @@coll.remove
 

test/test_objectid.rb

@@ -23,7 +23,7 @@ class ObjectIDTest < Test::Unit::TestCase
     doc = {:name => 'Mongo'}
     doc = ObjectID.create_pk(doc)
     assert doc[:_id]
-    
+
     doc = {:name => 'Mongo', :_id => '12345'}
     doc = ObjectID.create_pk(doc)
     assert_equal '12345', doc[:_id]
@@ -136,10 +136,19 @@ class ObjectIDTest < Test::Unit::TestCase
   def test_generation_time
     time = Time.now
     id   = ObjectID.new
+    generated_time = id.generation_time
 
-    assert_in_delta time.to_i, id.generation_time.to_i, 2
+    assert_in_delta time.to_i, generated_time.to_i, 2
+    assert_equal "UTC", generated_time.zone
   end
-  
+
+  def test_from_time
+    time = Time.now.utc
+    id   = ObjectID.from_time(time)
+
+    assert_equal time.to_i, id.generation_time.to_i
+  end
+
   def test_json
     id = ObjectID.new
     assert_equal %Q("#{id}"), id.to_json