@apiel/json-schema-decorator

Minimal library to merge JSON schema properties decorator into a JSON schema object.

import { generateJsonSchema, schema } from '@apiel/json-schema-decorator';

class Person {
  @schema({ maximum: 40, optional: true })
  age: number = 20;

  @schema({ maximum: 200 })
  height!: number;
}

const p = new Person();
console.log('This is the generated JSON schema', generateJsonSchema(p));

JSON schema output:

{
  type: 'object',
  required: [ 'height' ],
  properties: {
    age: { maximum: 40, type: 'number' },
    height: { maximum: 200, type: 'number' }
  }
}

To define a property schema, use the decorator @schema({}). The type of the property is inferred automatically and can still be overwritten if type is defined as parameter, e.g.: @schema({type: 'number'}). By default, properties are optional, to make them required, set the parameter optional to false, e.g.: @schema({optional: false}).

Generate the json schema by calling generateJsonSchema(the_target_object)

Validation

Validation is not include in this library, as the goal is simply to generate JSON schema. It's up to you to use the library of your choice for validation.

In our example, we will use AJV:

npm install ajv

import { generateJsonSchema, schema } from '@apiel/json-schema-decorator';
import Ajv from 'ajv';

class Person {
  @schema({ maximum: 40 })
  age: number = 20;

  @schema({ maximum: 200 })
  height: number = 223;
}

const p = new Person();
const jsonSchema = generateJsonSchema(p);

const ajv = new Ajv();
const validator = ajv.compile(jsonSchema);
const validation = validator(p);

// It should fail because height is over maximum limit
console.log('AJV validation result:', validation);
if (!validation) {
  console.error('Your object does not respect your JSON schema definition', validator.errors);
}

tsconfig

experimentalDecorators and emitDecoratorMetadata must be enable in your tsconfig.json.

{
  // ...
  "compilerOptions": {
    // ...
    "experimentalDecorators": true,
    "emitDecoratorMetadata": true
  }
}