Using zod union with generateObject

[risotto-master]

hi folks,

trying to use generateObject with a zod union:

const AppleSchema = z.object({
  type: z.literal("apple"),
  name: z.string(),
});

const OrangeSchema = z.object({
  type: z.literal("orange"),
  name: z.string(),
});

export const FruitSchema = z.discriminatedUnion("type", [
  AppleSchema,
  OrangeSchema,
]);

const result = await generateObject({
  model,
  messages: [
    {
      role: "user",
      content: [
        {
          type: "text",
          text: "Give me a fruit with a random name",
        },
      ],
    },
  ],
  schema: FruitSchema,
});

inspecting the schema that zod generates in this case:

{
  "anyOf": [
    {
      "type": "object",
      "properties": {
        "type": {
          "type": "string",
          "const": "apple"
        },
        "name": {
          "type": "string"
        }
      },
      "required": [
        "type",
        "name"
      ],
      "additionalProperties": false
    },
    {
      "type": "object",
      "properties": {
        "type": {
          "type": "string",
          "const": "orange"
        },
        "name": {
          "type": "string"
        }
      },
      "required": [
        "type",
        "name"
      ],
      "additionalProperties": false
    }
  ],
  "$schema": "http://json-schema.org/draft-07/schema#"
}

but apparently this does not work well with AI SDK when using gemini:

  data: {
    error: {
      code: 400,
      message: '* GenerateContentRequest.generation_config.response_schema.type: must be specified when not using one_of, any_of or all_of fields\n',
      status: 'INVALID_ARGUMENT'
    }
  },

or gpt4, albeit with a different error message:

  data: {
    error: {
      message: `Invalid schema for function 'json': schema must be a JSON Schema of 'type: "object"', got 'type: "None"'.`,
      type: 'invalid_request_error',
      param: 'tools[0].function.parameters',
      code: 'invalid_function_parameters'
    }
  },

behavior is the same whether i use .union or .discriminatedUnion.

however, using a schema that does not use an union sort of works:

export const FruitSchemaTwo = z.object({
  type: z.enum(["apple", "orange"]),
  name: z.string(),
});

i'm trying to re-use schemas I have elsewhere in the app so would like to avoid having to translate these objects. any idea what's going on?

[lgrammel]

Models don't have full support for all Zod schemas. There are several layers involved: Zod to JSON schema, and then the JSON schema support that the LLM provider offers / the LLM supports. Ideally the top level should be an object. Even with that though, there are limitations (especially in the union case, or when schemas get large)

[lgrammel]

Please check out https://sdk.vercel.ai/docs/ai-sdk-core/prompt-engineering

[Mnigos]

Having possibility to use union would be very helpful.