Add converter from type CoreMessage to type Message

[yudistiraashadi]

Feature Description

Reason

For persistence data which we save messages data to the Database, I think saving the data as Array<CoreMessage> makes more sense instead of saving it as Array<Message> as suggested on AI SDK docs. Array<CoreMessage> is used on the server which communicates with the DB, and it is also easier to add files as context like this example.

Solution

Add a converter from CoreMessage to Message to make it easier to translate the types. in AI Chatbot template they have a function called convertToUIMessages() link which helps translate their DB which looks like a raw CoreMessage to Message that is consumed by the UI. I think we can build something similar to that.

Use Cases

On server

streamText({
  ....
  onFinish: async (result) => {
    saveMessagesToDb(result.response.messages)
  }
})
....

On client

const savedMessages = getMessagesFromDB()

const chat = useChat({
  ...
  initialMessage: convertToUIMessages(savedMessages)
})

Additional context

No response

[lgrammel]

I strongly recommend not saving core messages. UI messages contain a lot of information that is required for correct persistence of UI state.

[yudistiraashadi]

I strongly recommend not saving core messages. UI messages contain a lot of information that is required for correct persistence of UI state.

I agree, but I argue it is better to save the messages state in DB as CoreMessage especially for file handling since UI Message only supports Image and Text based on here

[lgrammel]

Would saving UI messages work for you if they included attachments?

[yudistiraashadi]

yep, but I'm personally not happy making my DB structure based on currently experimental attachments structure of UIMessage. CoreMessage structure also afaik looks similar to the google and anthropic approach for file handling.

I'm currently using something similar to convertToUIMessages() based on Vercel's AI Chatbot repo, and I think that is a very good util function to be added to the AI SDK.

[tresorama]

I support @yudistiraashadi on making convertCoreMessageToUiMessage part of the sdk.
It would be very helpful.
Along with a zod schema to validate UIMessage, to have parity between core and ui message utilities.

// if you begin with core message and want a ui message...
const coreMessage = ...
const uiMessage = convertCoreMessageToUiMessage(coreMessage) // fn suggested (not present in sdk as today)
const parsedUiMessage = uiMessageSchema.parse(uiMessage) // zod schema suggested  (not present in sdk as today)

// opposite...
const uiMessage = ...
const coreMessage = convertToCoreMessage(uiMessage) // fn present in sdk as today
const parsedCoreMessage = coreMessageSchema.parse(coreMessage) // zod schema present in sdk as today