Specify controlled generation enum values in a JSON schema

Specify the list of response enum values in a JSON schema. The model selects an enum value from a list values that are defined in the schema.

Code sample

Go

Before trying this sample, follow the Go setup instructions in the Vertex AI quickstart using client libraries. For more information, see the Vertex AI Go API reference documentation.

To authenticate to Vertex AI, set up Application Default Credentials. For more information, see Set up authentication for a local development environment. 

import (
	"context"
	"errors"
	"fmt"
	"io"

	"cloud.google.com/go/vertexai/genai"
)

// controlledGenerationResponseSchemaEnum demonstrates how to constrain model responses
// to a predefined set of enum values for genre classification.
func controlledGenerationResponseSchemaEnum(w io.Writer, projectID, location, modelName string) error {
	// location = "us-central1"
	// modelName = "gemini-2.0-flash-001"
	ctx := context.Background()
	client, err := genai.NewClient(ctx, projectID, location)
	if err != nil {
		return fmt.Errorf("failed to create GenAI client: %w", err)
	}
	defer client.Close()

	model := client.GenerativeModel(modelName)

	model.GenerationConfig.ResponseMIMEType = "text/x.enum"
	model.GenerationConfig.ResponseSchema = &genai.Schema{
		Type: genai.TypeString,
		Enum: []string{"drama", "comedy", "documentary"},
	}

	prompt := `
The film aims to educate and inform viewers about real-life subjects, events, or people.
It offers a factual record of a particular topic by combining interviews, historical footage,
and narration. The primary purpose of a film is to present information and provide insights
into various aspects of reality.
`

	res, err := model.GenerateContent(ctx, genai.Text(prompt))
	if err != nil {
		return fmt.Errorf("failed to generate content: %w", err)
	}

	if len(res.Candidates) == 0 || len(res.Candidates[0].Content.Parts) == 0 {
		return errors.New("got empty response from model")
	}

	fmt.Fprintf(w, "Candidate label: %q", res.Candidates[0].Content.Parts[0])
	// Example response:
	// Candidate label: "documentary"

	return nil
}

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