Schema Valid

A Dart model validation library that uses annotations and code generation to provide type-safe, compile-time validated models.

Features

• Annotation-based validation - Decorate your model fields with validation annotations
• Code generation - Validation logic is generated at compile-time for maximum performance
• Null-safe - Only validates non-null values by default
• Custom error messages - Provide custom error messages for each validation rule
• Multiple validation methods - Choose between returning error lists or throwing exceptions

Installation

Add to your pubspec.yaml:

dependencies:
  schema_valid: ^0.0.1

dev_dependencies:
  build_runner: ^2.13.1

Usage

1. Add Annotations to Your Model

import 'package:schema_valid/schema_valid.dart';

class User {
  @NotEmpty(message: 'name cannot be empty')
  @Length(min: 2, max: 20, message: 'name must be between 2 and 20 characters')
  final String? name;

  @Email(message: 'email must be valid')
  final String? email;

  @Url(message: 'apiBaseUrl must be a valid URL')
  @NotEmpty(message: 'apiBaseUrl cannot be empty')
  final String apiBaseUrl;

  User(this.name, this.email, this.apiBaseUrl);
}

2. Run Code Generation

dart run build_runner build

3. Use Generated Validation Methods

import 'user.validator.dart';

void main() {
  final user = User('John', 'john@example.com', 'https://api.example.com');
  
  // Validate and get list of errors
  final errors = user.validate();
  if (errors.isEmpty) {
    print('User is valid!');
  } else {
    print('Validation errors: ${errors.join(', ')}');
  }
  
  // Or validate and throw exception on error
  try {
    user.validateOrThrow();
    print('User is valid!');
  } catch (e) {
    print('Validation failed: $e');
  }
}

Available Annotations

@NotEmpty

Validates that a string is not empty.

@NotEmpty(message: 'Field cannot be empty')
final String field;

@Length

Validates the length of a string.

@Length(min: 2, max: 50, message: 'Field must be between 2 and 50 characters')
final String field;

@Email

Validates that a string is a valid email format.

@Email(message: 'Must be a valid email address')
final String? email;

@Url

Validates that a string is a valid URL.

@Url(message: 'Must be a valid URL')
final String website;

Validation Behavior

• Null values are ignored by default (except for required fields)
• Multiple annotations can be applied to the same field
• Custom messages override default error messages
• Validation order follows the order of annotations

Generated Code

The library generates an extension on your model class with two methods:

• List<String> validate() - Returns a list of validation errors
• void validateOrThrow() - Throws ValidationException if validation fails

Example

See the example/ directory for a complete working example.

Development

To run the example:

cd example
dart run build_runner build
dart run user.dart

License

This project is licensed under the MIT License.