Add ability to clear namespaces (#202)

CHANGELOG.md

@@ -2,6 +2,9 @@
 
 ## x.y.z
 
+- Add ability to clear namespaces (#202). This operation can run for a very long time if the namespace contains
+  lots of keys! It should be used in tests, or when the namespace is small enough and you are sure you know what you are doing.
+
 ## 1.9.0
 
 - Accept Proc as a namespace (#203)

lib/redis/namespace.rb

@@ -338,6 +338,32 @@ def eval(*args)
     end
     ruby2_keywords(:eval) if respond_to?(:ruby2_keywords, true)
 
+    # This operation can run for a very long time if the namespace contains lots of keys!
+    # It should be used in tests, or when the namespace is small enough
+    # and you are sure you know what you are doing.
+    def clear
+      if warning?
+        warn("This operation can run for a very long time if the namespace contains lots of keys! " +
+             "It should be used in tests, or when the namespace is small enough " +
+             "and you are sure you know what you are doing.")
+      end
+
+      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?
@@ -599,5 +625,10 @@ def create_enumerator(&block)
         Enumerator.new(&block)
       end
     end
+
+    def supports_scan?
+      redis_version = @redis.info["redis_version"]
+      Gem::Version.new(redis_version) >= Gem::Version.new("2.8.0")
+    end
   end
 end

spec/redis_spec.rb

@@ -1053,4 +1053,30 @@
       expect(sub_sub_namespaced.full_namespace).to eql("ns:sub1:sub2")
     end
   end
+
+  describe :clear do
+    it "warns with helpful output" do
+      expect { @namespaced.clear }.to output(/can run for a very long time/).to_stderr
+    end
+
+    it "should delete all the keys" do
+      @redis.set("foo", "bar")
+      @namespaced.mset("foo1", "bar", "foo2", "bar")
+      capture_stderr { @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")
+      capture_stderr { @namespaced.clear }
+
+      expect(@redis.keys).to eq ["foo"]
+      expect(@namespaced.keys).to be_empty
+    end
+  end
 end