custom_validators

Custom Validators Example

This example demonstrates how to create and use custom validators with GoZod.

Features Demonstrated

1. Creating custom validators - Implement your own validation logic
2. Parameterized validators - Validators that accept configuration parameters
3. Validator registration - Register validators directly in your application
4. Struct tag integration - Use custom validators in struct tags
5. Programmatic usage - Use validators without struct tags

Example Validators

The example includes three types of custom validators:

1. Basic Validator (UniqueUsernameValidator)

• Type: string
• Tag: unique_username
• Purpose: Validates username uniqueness (simulated database check)

2. Parameterized Int Validator (MinValueValidator)

• Type: int
• Tag: min_value=N
• Purpose: Validates minimum integer value
• Example: min_value=18 for age validation

3. Parameterized String Validator (PrefixValidator)

• Type: string
• Tag: prefix=PREFIX
• Purpose: Validates string prefix
• Example: prefix=PROD for product SKUs

Usage

Struct Tag Usage

type User struct {
    Username string `gozod:"required,unique_username"`
    Email    string `gozod:"required,email"`
    Age      int    `gozod:"required,min_value=18"`
}

type Product struct {
    SKU   string `gozod:"required,prefix=PROD"`
    Name  string `gozod:"required,min=3,max=100"`
    Price int    `gozod:"required,min_value=1"`
}

Registration

func registerCustomValidators() {
    validators.Register(&UniqueUsernameValidator{})
    validators.Register(&PrefixValidator{})
    validators.Register(&MinValueValidator{})
}

Programmatic Usage

// Get validator from registry
validator, _ := validators.Get[string]("unique_username")

// Use with schema
schema := gozod.String().
    Min(3).
    Max(20).
    Refine(validators.ToRefineFn(validator))

Running the Example

cd examples/custom_validators
go run main.go

Output

The example demonstrates:

• ✅ Successful validation of valid data
• ✅ Rejection of invalid data with clear error messages
• ✅ Both struct tag and programmatic usage patterns

Creating Your Own Validators

To create a custom validator:

1. Implement the interface:

type MyValidator struct{}

func (v *MyValidator) Name() string { return "my_validator" }
func (v *MyValidator) Validate(value T) bool { /* logic */ }
func (v *MyValidator) ErrorMessage(ctx *core.ParseContext) string { /* message */ }

1. For parameterized validators, also implement:

func (v *MyValidator) ValidateParam(value T, param string) bool { /* logic */ }
func (v *MyValidator) ErrorMessageWithParam(ctx *core.ParseContext, param string) string { /* message */ }

1. Register at startup:

validators.Register(&MyValidator{})

1. Use in struct tags or programmatically:

type MyStruct struct {
    Field string `gozod:"my_validator"`
}