@candra-dev/validator-core

Decorator-based validation library for Angular Reactive Forms.
Define validation rules directly inside TypeScript model classes using decorators — similar to DTO validation in NestJS.

This library allows you to keep validation rules centralized, consistent, reusable, and highly scalable for enterprise applications.

✨ Features

• ✔ Decorator-based validation (@Required, @MinLength, @Regex, @Custom, ...)
• ✔ Centralized rules in model classes (similar to NestJS DTO)
• ✔ Works with Angular Reactive Forms
• ✔ Custom error message provider (injectable)
• ✔ Minimal, zero dependencies (except reflect-metadata)
• ✔ Fully tree-shakeable Angular library
• ✔ Supports dynamic + custom validation logic

📦 Installation

Install from NPM:

npm install @candra-dev/validator-core reflect-metadata



Add to main.ts (or polyfills.ts):
import 'reflect-metadata';

import { ValidatorCoreModule } from '@candra-dev/validator-core';

@NgModule({
  imports: [
    ValidatorCoreModule.forRoot()
  ]
})
export class AppModule {}


🧭 Step-by-Step Guide
⭐ Step 1 — Create a Model Class With Decorators

// src/app/models/login.model.ts

import { Required, MinLength } from '@candra-dev/validator-core';

export class LoginModel {
  @Required()
  username!: string;

  @Required()
  @MinLength(6)
  password!: string;
}


⭐ Step 2 — Build a Reactive Form Using the Model
// src/app/login/login.component.ts

import { Component } from '@angular/core';
import { FormBuilder } from '@angular/forms';
import { buildValidator } from '@candra-dev/validator-core';
import { LoginModel } from '../models/login.model';

@Component({
  selector: 'app-login',
  templateUrl: './login.component.html'
})
export class LoginComponent {
  form = this.fb.group({
    username: [''],
    password: ['']
  }, {
    validators: buildValidator(LoginModel)
  });

  constructor(private fb: FormBuilder) {}

  submit() {
    console.log(this.form.value);
  }
}


⭐ Step 3 — Display Errors in Template
<form [formGroup]="form" (ngSubmit)="submit()">

  <input formControlName="username" placeholder="Username" />
  <div *ngIf="form.errors?.username?.required">
    Username is required.
  </div>

  <input formControlName="password" placeholder="Password" />
  <div *ngIf="form.errors?.password?.minLength">
    Password must be at least 6 characters.
  </div>

  <button type="submit">Login</button>
</form>

🧠 Built-in Decorators
| Decorator           | Description             |
| ------------------- | ----------------------- |
| `@Required()`       | Cannot be empty         |
| `@MinLength(n)`     | Minimum length          |
| `@MaxLength(n)`     | Maximum length          |
| `@Regex(/pattern/)` | Must match pattern      |
| `@Custom(fn)`       | Custom validation logic |

🔥 Custom Validator Example
import { Required, Custom } from '@candra-dev/validator-core';

export class RegisterModel {
  @Required()
  password!: string;

  @Required()
  @Custom((value, obj) => value === obj.password)
  confirmPassword!: string;
}


🎨 Custom Error Messages (Optional)
You can override all default messages.
1️⃣ Create your own provider
// src/app/services/my-error-messages.ts

import { IErrorMessageProvider } from '@candra-dev/validator-core';

export class MyErrorMessages implements IErrorMessageProvider {
  getMessage(key: string, ctx?: any): string {
    switch (key) {
      case 'required':
        return 'Wajib diisi!';
      case 'minLength':
        return `Minimal ${ctx?.min} karakter`;
      default:
        return 'Data tidak valid.';
    }
  }
}


2️⃣ Register it in AppModule
ValidatorCoreModule.forRoot({
  useClass: MyErrorMessages
})

Done — now your custom messages apply globally.


🔧 Full Decorator Example
export class ProductModel {
  @Required()
  name!: string;

  @MinLength(3)
  @MaxLength(50)
  description!: string;

  @Regex(/^[0-9]+$/)
  price!: string;

  @Custom((value, all) => value <= all.maxStock)
  quantity!: number;

  maxStock = 100;
}

⚙ API Reference
buildValidator(ModelClass)
Creates an Angular validator that reads metadata from model decorators.
form = fb.group({ ... }, { validators: buildValidator(MyModel) });


Decorators

    @Required()

    @MinLength(n)

    @MaxLength(n)

    @Regex(/pattern/)

    @Custom(fn)

Injection Token

ERROR_MESSAGE_PROVIDER

📄 License
MIT License © 2025 Candra