Context switching

Advanced feature

In a single account, any number of chatbot projects can be created.

tip

Tovie Platform has a special feature which allows switching the dialog context from a bot in one project to a bot from another.

This article will explain:

1. What a bot stack is.
2. How to switch and return the context.
3. Other usage notes on this feature.

Bot stack

For each bot deployed in Tovie Platform, a number of resources is allocated for switching the context to other bots. Bots participating in context switching are organized in a stack.

If the bot script does not involve context switching, its stack always remains the same. Changing the bot context can be achieved in two ways:

• Context switch: the dialog context is passed to another bot. This other bot is pushed onto the bot stack.
• Context return: the last bot is popped from the stack, and the context is returned to the previous bot.

When the context is changed, the bot changes its mode of operation as if it were another bot. However, the communication channel remains the same. This allows implementing complex behavior for interacting with clients.

caution

Bots which participate in context switching must share the same account. Switching the context to a bot from another account will result in an error.

Context switch

To switch the context from the bot script, push an object with the following properties to $response.replies.

Property	Type	Required	Description
type	String	Yes	The type of the reply in the $response.replies array. Must be equal to "context-switch".
targetBotId	String	Yes	The ID of the bot where context should be switched. You can find it in the properties of the channel where the bot is deployed.
targetState	String	No	The absolute path to the state where a transition will be made after switching the context. If you don’t pass targetState, the request will be processed in the root theme / after the context has been switched. The appropriate state will be selected at runtime. If the other bot has handlers, all handlers except preMatchwill be executed by default when switching.
parameters	Object	Yes	Arbitrary data that needs to be passed to another bot. After switching the context, this object will be available in $request.data.

state: SwitchToFrench
    q!: * (switch to/speak) French *
    script:
        $response.replies = $response.replies || []; // `$response.replies` array setup
        $response.replies.push({
            type: "context-switch",
            targetBotId: "13721-frBot-13721-BkN-41730",
            targetState: "/Start",
            parameters: {}
        });

caution

The data passed as $request.data will be available from another bot only during the processing of the current request. Store it in $session or $client if you need to have access to it later.

Context return

After the context has been switched, the script of the previous bot is no longer available. The context must be explicitly returned from the new bot script to the script where switching took place.

To return the context to the previous bot script, push an object with the following properties to the $response.replies array.

Property	Type	Required	Description
type	String	Yes	The type of the reply in the $response.replies array. Must be equal to "context-return".
state	String	No	The absolute path to the state where a transition will be made after switching the context. If you don’t pass state, the request will be processed in the root theme / after the context has been returned. The appropriate state will be selected at runtime.
data	Object	Yes	Arbitrary data that needs to be passed to another bot. After returning the context, this object will be available in $request.data.

state: SwitchToEnglish
    q!: * (switch to/speak) English *
    script:
        $response.replies = $response.replies || []; // `$response.replies` array setup
        $response.replies.push({
            type: "context-return",
            state: "/Start",
            data: {}
        });

Usage notes

Stack overflow

Theoretically, switching the context back to the previous bot can be done with context-switch. However, this usage is incorrect, because the same bot will be pushed onto the stack multiple times.

caution

The capacity of the stack for each bot is limited. In order to avoid a stack overflow, only context-return must be used for returning the context.

Event processing

If the context is switched from an example bot 1 to an example bot 2, all requests from the client will be processed in the context of bot 2.

However, if a timeout or an event which can be processed in bot 1 occurs in the channel, the event will be processed in the appropriate state. The context will be automatically returned to bot 1.

caution

This behavior is true only for custom events created with one of the $pushgate built-in service methods and does not apply to system events.

tip

If this automatic context return is not the intended behavior, use the noContext flag for the state where the event is handled.

Learn how to use context switching in practice by walking through the multilingual bot tutorial.

Handler execution in context switch

If you transitioned to the second bot’s state using context switch, all relevant handlers from the second bot’s script will be executed by default, except preMatch. You can also change this behavior for each handler using the allowedInContextSwitch argument of the bind function.

tip

The allowedInContextSwitch argument is applied only when the handlers are called for the first time after the transition to the second bot.