Reusable Go Validation Functions

Reuse a validation session

validatePreStatus := func(status string) *v.Validation {
  regex, _ := regexp.Compile("pre-.+")
  return v.Is(v.String(status, "status").Not().Blank().MatchingTo(regex))
}

val := v.Is(
  v.String(r.Name, "name").Not().Blank(),
  v.String(r.Status, "status").Not().Blank(),
)

val.Merge(validatePreStatus(r.Status))

Reuse a stateless predicate

When you only need a boolean result, import github.com/cohesivestack/valgo/is. Predicates contain the same rule logic as Valgo’s built-in validators, without field names, error messages, localization, or validation sessions.

import "github.com/cohesivestack/valgo/is"

func validUsername(username string) bool {
  return is.StringLengthBetween(username, 3, 30) &&
    !is.StringBlank(username)
}

The same function can be reused inside a validator when an error message is needed:

val := v.Is(
  v.String(input.Username, "username").
    Passing(validUsername, "{{title}} must be 3-30 non-blank characters"),
)

See Stateless Predicates for the available families and pointer behavior.