Add mexists method that allow to check the existance of multiple keys

lib/redis.rb

@@ -559,6 +559,16 @@ def exists(key)
     end
   end
 
+  # Count existing keys.
+  #
+  # @param [Array<String>] key
+  # @return [Fixnum]
+  def mexists(*keys)
+    synchronize do |client|
+      client.call([:exists] + keys)
+    end
+  end
+
   # Find all keys matching the given pattern.
   #
   # @param [String] pattern

lib/redis/distributed.rb

@@ -174,6 +174,14 @@ def exists(key)
       node_for(key).exists(key)
     end
 
+    # Count existing keys.
+    def mexists(*args)
+      keys_per_node = args.group_by { |key| node_for(key) }
+      keys_per_node.inject(0) do |sum, (node, keys)|
+        sum + node.mexists(*keys)
+      end
+    end
+
     # Find all keys matching the given pattern.
     def keys(glob = "*")
       on_each_node(:keys, glob).flatten

test/lint/value_types.rb

@@ -10,6 +10,18 @@ def test_exists
       assert_equal true,  r.exists("foo")
     end
 
+    def test_mexists
+      refute r.exists(["foo", "baz"])
+
+      r.set("foo", "s1")
+
+      assert_equal 1,  r.mexists(["foo", "baz"])
+
+      r.set("baz", "s2")
+
+      assert_equal 2,  r.mexists(["foo", "baz"])
+    end
+
     def test_type
       assert_equal "none", r.type("foo")