Govalid

Use Govalid to validate structs.

Basic Example

package main

import (
	"errors"
	"fmt"
	"log"
	"strings"
	"unicode/utf8"

	"github.com/twharmon/govalid"
)

type Post struct {
	// ID has no constraints
	ID int

	// Title is required, must be at least 3 characters long, and
	// cannot be more than 20 characters long
	Title string `valid:"req|min:3|max:20"`

	// Body is not required, cannot be more than 10000 charachers,
	// and must be "fun" (a custom rule defined below).
	Body string `valid:"max:10000|fun"`
}

func main() {
	// Add custom string rule "fun" that can be used on any string field
	// in any struct.
	govalid.Rule("fun", func(v any) error {
		switch tv := v.(type) {
		case string:
			if float64(strings.Count(tv, "!"))/float64(utf8.RuneCountInString(tv)) > 0.001 {
				return nil
			}
			// return a validation error with govalid.Error
			return govalid.NewValidationError("must contain more exclamation marks")
		default:
			// return a non validation (internal) error
			return errors.New("fun constraint must be applied to string only")
		}
	})
	fmt.Println(govalid.Validate(&Post{
		ID:    5,
		Title: "Hi",
		Body:  "Hello world!",
	}))
}

Error Values

When you call govalid.Validate to validate a struct, it returns an error if the validation rules are not met. This error may either be a validation-specific error (an implementation of govalid.ValidationError) or a different error indicating a problem in processing the validation. This allows you to distinguish between errors caused by invalid data and those caused by issues in your validation logic, such as setting the valid tag to max:not-a-number.

if err := govalid.Validate(value); err != nil {
	verr, ok := err.(govalid.ValidationError)
	if ok {
		fmt.Println("validation error", err)
	} else {
		fmt.Println("some other error", err)
	}
}

Dive Usage

The dive rule is used to apply validation rules to elements within pointers, slices, arrays, and structs. When the dive rule is encountered, it instructs the validator to "dive" into the elements of the collection or the value pointed to by a pointer and apply the remaining rules to each element or the dereferenced value.

Notes

• Pointers: The dive rule will dereference the pointer and apply the remaining rules to the value it points to.
• Slices/Arrays: The dive rule will iterate over each element in the slice or array and apply the remaining rules to each element.
• Structs: The dive rule will validate the struct according to its own field tags. The remaining rules after dive have no meaning for structs.

Examples

Pointers

type Example struct {
    Field *string `valid:"req|dive|min:3"`
}

In this example, the Field must be a non-nil pointer to a string, and the string must be at least 3 characters long.

Slices/Arrays

type Example struct {
    Field []string `valid:"req|dive|min:3"`
}

In this example, the Field must be a non-nil slice of strings, and each string in the slice must be at least 3 characters long.

Structs

type Inner struct {
    Name string `valid:"req"`
}

type Outer struct {
    InnerStruct Inner `valid:"dive"`
}

In this example, the InnerStruct field will be validated according to the validation tags defined in the Inner struct.

Contribute

Make a pull request.