Validation

Validation runs before every insert and update, and a failure stops the write. It runs at the same point as hooks, so bulk writes skip it, and so does ant.WithoutHooksfunc WithoutHooks(ctx context.Context) context.ContextWithoutHooks skips model hooks for writes made with ctx..

A Validate method

For rules that span fields, give the model a Validate method.

type Signup struct {
	ID    int64
	Name  string
	Email string
	Age   int
}

func (s *Signup) Validate(ctx context.Context) error {
	if s.Name == "" {
		return errors.New("name is required")
	}

	return nil
}

Field rules

b.Validatefunc (b *ModelBuilder[E]) Validate[V any](field *V, rule func(V) error)Validate adds a rule for a field, checked before Insert and SaveChanges write it, as a Validate hook is. attaches a rule to a single field, typed to that field. The validate package has the common ones ready to go.

func (Signup) Configure(b *ant.ModelBuilder[Signup]) {
	b.Validate(&S.Name, validate.All(validate.Required[string](), validate.MaxLength(50)))
	b.Validate(&S.Email, validate.Email)
	b.Validate(&S.Age, validate.Range(0, 150))
}

var S = ant.Fields[Signup]()

Rule	Checks
validate.Required[V]()func Required[V any]() func(V) errorRequired rejects the zero value.	Not the zero value
validate.Emailfunc Email(v string) errorEmail rejects a string that is not an email address.	A valid address
validate.MinLength(n)func MinLength(n int) func(string) errorMinLength rejects a string with fewer characters than n., validate.MaxLength(n)func MaxLength(n int) func(string) errorMaxLength rejects a string with more characters than n.	String length
validate.Range(low, high)func Range[V cmp.Ordered](low, high V) func(V) errorRange rejects a value outside low and high, inclusive.	Between two values
validate.OneOf(a, b, c)func OneOf[V comparable](allowed ...V) func(V) errorOneOf rejects a value not in the list.	One of these
validate.Matches(pattern)func Matches(pattern *regexp.Regexp) func(string) errorMatches rejects a string that does not match pattern.	Matches a *regexp.Regexp
validate.All(rules...)func All[V any](rules ...func(V) error) func(V) errorAll runs rules in order, stopping at the first failure.	All of them

A rule is just a func(V) error, so writing your own is easy.

Reading the error

A failed rule comes back as an ant.ValidationErrortype ValidationError struct{ … }ValidationError reports a field that failed a rule from ModelBuilder.Validate., which tells you the field.

err := db.Signups.Insert(ctx, &Signup{Email: "a@example.com"})

var invalid *ant.ValidationError

if errors.As(err, &invalid) {
	fmt.Println(invalid.Field, invalid.Err) // Name, and why
}

See it tested: tests/features/lifecycle/validate_test.go