Validation

The validation package wraps go-playground/validator and produces user-friendly field error messages.

Import

import "github.com/slice-soft/ss-keel-core/validation"

Validate

func Validate(s any) []FieldError

Validates a struct using validate struct tags. Returns nil if the struct is valid.

type CreateUserDTO struct {
    Name  string `json:"name"  validate:"required"`
    Email string `json:"email" validate:"required,email"`
    Age   int    `json:"age"   validate:"min=18"`
}

dto := CreateUserDTO{Name: "", Email: "invalid", Age: 15}
errors := validation.Validate(&dto)

// errors:
// [
//   { "field": "name",  "message": "this field is required" },
//   { "field": "email", "message": "must be a valid email" },
//   { "field": "age",   "message": "minimum 18 characters" },
// ]

FieldError

type FieldError struct {
    Field   string `json:"field"`
    Message string `json:"message"`
}

Supported Tags & Messages

Tag	Message
required	this field is required
email	must be a valid email
min=N	minimum N characters
max=N	maximum N characters
uuid	must be a valid UUID
uuid4	must be a valid UUID
numeric	must be a numeric value
url	must be a valid URL

For any unrecognized tag, the raw validator message is used as a fallback.

Integration with ParseBody

Ctx.ParseBody calls Validate internally. You don’t need to call it manually when using ParseBody:

func (c *UserController) create(ctx *core.Ctx) error {
    var dto CreateUserDTO
    if err := ctx.ParseBody(&dto); err != nil {
        // 400 Bad Request  — malformed JSON
        // 422 Unprocessable Entity — validation errors
        return err
    }
    // dto is valid here
}

The 422 response body:

{
  "errors": [
    { "field": "email", "message": "must be a valid email" },
    { "field": "name",  "message": "this field is required" }
  ]
}

Standalone Usage

You can call Validate independently of ParseBody:

type UpdateProfileDTO struct {
    Bio  string `validate:"max=500"`
    URL  string `validate:"omitempty,url"`
}

dto := UpdateProfileDTO{Bio: strings.Repeat("x", 600), URL: "not-a-url"}
if errs := validation.Validate(&dto); errs != nil {
    // handle errs
}

Validate Tags Reference

For a full list of available validator tags, see the go-playground/validator documentation.