Any way allow to customize key of KTable

[kumin]

How can I change the key of message when I save a value to KTable in Callback? Or Use another key when Output to other topics? For Example: I have a event click topic and key of message in this topic is random number, so I want to transform messages to other topics with the key is user-id which is contained in the message.

[frairon]

With KTable, do you mean that another processor will work on the table, or that you want to store the message under a different key in the same processor? For the case of another processor, just emit the message to another topic/table with the new key, like this:

goka.NewProcessor(... , 
	goka.DefineGroup(... ,
		goka.Input("topic", codec, func(ctx goka.Context, msg interface{}){
	   value := msg.(MessageType)
     ctx.Emit("new-key-topic", value.NewKey, msg)
	}),
	goka.Output("new-key-topic", codec)),
)

If it's within the same processor, use the loop-edge, which provides a way to send a message to the same processor using an auto-created topic.

goka.NewProcessor(... ,
	goka.DefineGroup(... ,goka.Input("topic", codec, func(ctx goka.Context, msg interface{}){
    value := msg.(MessageType)
    ctx.Loopback(value.NewKey, msg)
	}),
	goka.Loop(codec, func(ctx goka.Context, msg interface{}){
		// here we'll receive msg with the correct key and can simply store it
		ctx.SetValue(msg)
	}),
	goka.Persist(codec),
)

The code above is more pseudo code of course, you'd have to take care of actual codecs and topic names and such.

Hope that helps, let me know if you have more questions.