Custom Validators

You can write custom validations that give users feedback about required syntax, types, and acceptable values in your provider. The Framework has a collection of predefined validators. Refer to Predefined Validators to learn how to use them.

This page explains how to migrate attribute validation functions from SDKv2 to attribute validators in the Framework.

SDKv2

In SDKv2, arbitrary validation logic can be applied to individual attributes by using ValidateFunc and/or ValidateDiagFunc.

The following example shows the implementation of a validation that ensures that an integer attribute has a value greater than one.

func resourceExample() *schema.Resource {
    return &schema.Resource{
        /* ... */
        Schema: map[string]*schema.Schema{
            "attribute_example": {
                ValidateDiagFunc: validation.ToDiagFunc(validation.IntAtLeast(1)),
                /* ... */

Framework

In the Framework, you implement either type of validation by setting the Validators field on the schema.Attribute implementation.

The following example shows how to implement a validation that ensures that an integer attribute has a value greater than one.

func (r *ThingResource) Schema(ctx context.Context, req resource.SchemaRequest, resp *resource.SchemaResponse) {
    resp.Schema = schema.Schema{
        /* ... */
        Attributes: map[string]schema.Attribute{
            "attribute_example": schema.Int64Attribute{
                Validators: []validator.Int64{
                    int64validator.AtLeast(1),
                    /* ... */

Migration Notes

Remember the following details when migrating from SDKv2 to the Framework.

In SDKv2, ValidateDiagFunc is a field on schema.Schema that you can use to define custom validation functions. In the Framework, Validators is a field on each schema.Attribute implementation that can be used for custom validations.
Use predefined validators when there is a validator that meets your requirements.

Example

SDKv2

The following example shows the implementation of the ValidateDiagFunc field for the exampleResource's example_attribute attribute to validate that it's value is at least 1 (greater than zero).

func exampleResource() *schema.Resource {
    return &schema.Resource{
        Schema: map[string]*schema.Schema{
            "example_attribute": {
                ValidateDiagFunc: validation.ToDiagFunc(validation.IntAtLeast(1)),
            },
        },
    }
}

Framework

The following shows the same section of provider code after the migration.

This code validates that the exampleResource's example_attribute attribute is greater than zero by using a custom AtLeast validator.

func (r *exampleResource) Schema(ctx context.Context, req resource.SchemaRequest, resp *resource.SchemaResponse) {
    resp.Schema = schema.Schema{
        Attributes: map[string]schema.Attribute{
            "example_attribute": schema.Int64Attribute{
                Required: true,
                Validators: []validator.Int64{
                    int64validator.AtLeast(1),
                },
            },
        },
    }
}

This example code illustrates how you can implement your own validators.

var _ validator.Int64 = atLeastValidator{}

// atLeastValidator validates that an integer Attribute's value is at least a certain value.
type atLeastValidator struct {
    min int64
}

// Description describes the validation in plain text formatting.
func (v atLeastValidator) Description(_ context.Context) string {
    return fmt.Sprintf("value must be at least %d", v.min)
}

// MarkdownDescription describes the validation in Markdown formatting.
func (v atLeastValidator) MarkdownDescription(ctx context.Context) string {
    return v.Description(ctx)
}

// Validate performs the validation.
func (v atLeastValidator) ValidateInt64(ctx context.Context, request validator.Int64Request, response *validator.Int64Response) {
    if req.ConfigValue.Int64Value() < v.min {
        response.Diagnostics.Append(validatordiag.InvalidAttributeValueDiagnostic(
            request.Path,
            v.Description(ctx),
            fmt.Sprintf("%d", req.ConfigValue.Int64Value()),
        ))
    }
}

// AtLeast returns an AttributeValidator which ensures that any configured
// attribute value:
//
//     - Is a number, which can be represented by a 64-bit integer.
//     - Is exclusively greater than the given minimum.
//
// Null (unconfigured) and unknown (known after apply) values are skipped.
func AtLeast(min int64) validator.Int64 {
    return atLeastValidator{
        min: min,
    }
}