lemonade 0.1.1

Simple, typesafe, object-oriented library for data validation

lemonade

Simple yet powerful library for data validation:

• Fully compile-, type- and null-safe API
• Universal for any standard data structures
• Written in pure dart
• 0 dependencies

Mainly inspired by semantics of JSON Schema and ajv.

Usage

For example, you want to validate GeoJSON point object that looks like this:

{
    "type": "Point",
    "coordinates": [125.6, 10.1]
}

Validator for this schema will look like that:

final pointsValidator = Validator.object(
  items: {
    // "type": "Point"
    'type': Validator.equals('Point'),
    // "coordinates": [125.6, 10.1]
    'coordinates': Validator.list(
      item: Validator.number(),
      // Length exactly 2
      minItems: 2,
      maxItems: 2,
    ),
  },
);

Then you can check if any data looks like with very basic method:

final decodedData = jsonDecode('{"type":"Point","coordinates":[125.6,10.1]}');

print(pointsValidator.validate(decodedData)); // true

If you want to check, what exactly is wrong, you can use getError method:

final wrongData = jsonDecode('{"type":"Point","coordinates":[125.6,"10.1"]}');

print(pointsValidator.getError(wrongData)); // object.coordinates > list<number>[1] > expected(number).got(10.1)

String representation of the errors says that:

• In field "coordinates"
  • At index [1]
    • Expected any number
    • Got "10.1"

It's easy to decode and trace an error in your data, isn't it?

Features and roadmap

I started this project in my own urgent need to write huge amount of JSON validators. Then I tried to make it more universal so it can be used in other use cases.

• ✅ Validators for the most basic types
• ❌ Built-in validators for most common data types
• ❌ Built-in validators for custom data structures
• ❌ Full backwards compatibility with JSON Schema
• ❌ Automatic HTTP response validation on client-side
• ❌ Automatic HTTP request validation on server-side