Skip to main content

Overview

model — defaults & validation for Go structs​

model is a tiny helper that binds a Model to your struct. It can:

  • Set defaults from struct tags like default:"…" and defaultElem:"…".
  • Validate fields using named rules from validate:"…" and validateElem:"…".
  • Accumulate all issues into a single ValidationError (no fail-fast).
  • Recurse through nested structs, pointers, slices/arrays, and map values.

It’s designed to be small, explicit, and type-safe (uses generics). You register rules (via NewRule) and model handles traversal, dispatch, and error reporting. Built‑in rules are always available implicitly (you don’t have to register them unless you want to override their behavior).

Quick start​

package main

import (
    "context"
    "encoding/json"
    "errors"
    "fmt"
    "time"

    "github.com/ygrebnov/model"
)

type User struct {
    Name    string        `default:"Anonymous" validate:"nonempty"`
    Age     int           `default:"18"        validate:"positive,nonzero"`
    Timeout time.Duration `default:"1s"`
}

func main() {
    u := User{}

    m, err := model.New(&u,
        model.WithDefaults[User](),
        model.WithValidation[User](context.Background()),
    )
    if err != nil {
        var ve *model.ValidationError
        if errors.As(err, &ve) {
            b, _ := json.MarshalIndent(ve, "", "  ")
            fmt.Println(string(b))
        } else {
            fmt.Println("error:", err)
        }
        return
    }

    _ = m
    fmt.Printf("User after defaults: %+v\n", u)
}

See Installation and Examples for more.