Added Collection#distinct [RUBY-61]

lib/mongo/collection.rb

@@ -383,6 +383,28 @@ EOS
       return @db.eval(Code.new(group_function, scope))["result"]
     end
 
+    # Returns a list of distinct values for +key+ across all
+    # documents in the collection. The key may use dot notation
+    # to reach into an embedded object.
+    #   @collection.save({:zip => 10010, :name => {:age => 27}})
+    #   @collection.save({:zip => 94108, :name => {:age => 24}})
+    #   @collection.save({:zip => 10010, :name => {:age => 27}})
+    #   @collection.save({:zip => 99701, :name => {:age => 24}})
+    #   @collection.save({:zip => 94108, :name => {:age => 27}})
+    #
+    #   @collection.distinct(:zip)
+    #     [10010, 94108, 99701]
+    #   @collection.distinct("name.age")
+    #     [27, 24]
+    def distinct(key)
+      raise MongoArgumentError unless [String, Symbol].include?(key.class)
+      command = OrderedHash.new
+      command[:distinct] = @name
+      command[:key]        = key.to_s
+
+      @db.db_command(command)["values"]
+    end
+
     # Rename this collection.
     #
     # If operating in auth mode, client must be authorized as an admin to

lib/mongo/errors.rb

@@ -21,6 +21,9 @@ module Mongo
   # Raised when configuration options cause connections, queries, etc., to fail.
   class ConfigurationError < MongoRubyError; end
 
+  # Raised when invalid arguments are sent to Mongo Ruby methods.
+  class MongoArgumentError < MongoRubyError; end
+
   # Raised when a database operation fails.
   class OperationFailure < RuntimeError; end
 

test/test_collection.rb

@@ -59,6 +59,21 @@ class TestCollection < Test::Unit::TestCase
     assert_equal 5, @@db.collection("test.foo").find_one()["x"]
   end
 
+  if @@version > "1.1"
+    def test_distinct
+      @@test.remove
+      @@test.insert([{:a => 0, :b => {:c => "a"}},
+                     {:a => 1, :b => {:c => "b"}},
+                     {:a => 1, :b => {:c => "c"}},
+                     {:a => 2, :b => {:c => "a"}},
+                     {:a => 3},
+                     {:a => 3}])
+
+      assert_equal [0, 1, 2, 3], @@test.distinct(:a).sort
+      assert_equal ["a", "b", "c"], @@test.distinct("b.c").sort
+    end
+  end
+
   def test_safe_insert
     a = {"hello" => "world"}
     @@test.insert(a)