Add ability to clear namespaces

lib/redis/namespace.rb

@@ -329,6 +329,23 @@ def eval(*args)
     end
     ruby2_keywords(:eval) if respond_to?(:ruby2_keywords, true)
 
+    def clear
+      batch_size = 1000
+
+      if supports_scan?
+        cursor = "0"
+        begin
+          cursor, keys = scan(cursor, count: batch_size)
+          del(*keys) unless keys.empty?
+        end until cursor == "0"
+      else
+        all_keys = keys("*")
+        all_keys.each_slice(batch_size) do |keys|
+          del(*keys)
+        end
+      end
+    end
+
     ADMINISTRATIVE_COMMANDS.keys.each do |command|
       define_method(command) do |*args, &block|
         raise NoMethodError if deprecations?
@@ -581,5 +598,10 @@ def create_enumerator(&block)
         Enumerator.new(&block)
       end
     end
+
+    def supports_scan?
+      redis_version = Gem::Version.new(@redis.info["redis_version"])
+      redis_version >= Gem::Version.new("2.8.0")
+    end
   end
 end

spec/redis_spec.rb

@@ -949,4 +949,26 @@
       expect(sub_sub_namespaced.full_namespace).to eql("ns:sub1:sub2")
     end
   end
+
+  describe :clear do
+    it "should delete all the keys" do
+      @redis.set("foo", "bar")
+      @namespaced.mset("foo1", "bar", "foo2", "bar")
+      @namespaced.clear
+
+      expect(@redis.keys).to eq ["foo"]
+      expect(@namespaced.keys).to be_empty
+    end
+
+    it "should delete all the keys in older redis" do
+      allow(@redis).to receive(:info).and_return({ "redis_version" => "2.7.0" })
+
+      @redis.set("foo", "bar")
+      @namespaced.mset("foo1", "bar", "foo2", "bar")
+      @namespaced.clear
+
+      expect(@redis.keys).to eq ["foo"]
+      expect(@namespaced.keys).to be_empty
+    end
+  end
 end