JSON Schema Integration

Ack schemas can be automatically converted into JSON Schema objects, allowing you to generate API documentation directly from your validation schemas.

Generating JSON Schemas

Use the toJsonSchema() method available on any AckSchema instance.

import 'package:ack/ack.dart';
import 'dart:convert';

// Example User Schema
final userSchema = Ack.object({
  'id': Ack.integer().positive().describe('Unique user identifier'),
  'name': Ack.string().minLength(2).maxLength(50).describe('User\'s full name'),
  'email': Ack.string().email().describe('User\'s email address'),
  'role': Ack.enumValues(UserRole.values).withDefault(UserRole.user),
  'isActive': Ack.boolean().withDefault(true),
  'tags': Ack.list(Ack.string()).unique().describe('List of user tags').nullable(),
  'age': Ack.integer().min(0).max(120).nullable().describe('User\'s age'),
}).describe('Represents a user in the system');

void main() {
  // Convert the AckSchema to a JSON Schema Object Map
  final jsonSchemaMap = userSchema.toJsonSchema();

  // Pretty print the JSON representation of the JSON Schema
  final jsonEncoder = JsonEncoder.withIndent('  ');
  print(jsonEncoder.convert(jsonSchemaMap));
}

Output JSON (JSON Schema Object):

{
  "type": "object",
  "description": "Represents a user in the system",
  "properties": {
    "id": {
      "type": "integer",
      "description": "Unique user identifier",
      "exclusiveMinimum": 0
    },
    "name": {
      "type": "string",
      "description": "User\'s full name",
      "minLength": 2,
      "maxLength": 50
    },
    "email": {
      "type": "string",
      "format": "email",
      "description": "User\'s email address"
    },
    "role": {
      "type": "string",
      "enum": [
        "admin",
        "user",
        "guest"
      ],
      "default": "user"
    },
    "isActive": {
      "type": "boolean",
      "default": true
    },
    "tags": {
      "anyOf": [
        {
          "type": "array",
          "description": "List of user tags",
          "items": {
            "type": "string"
          },
          "uniqueItems": true
        },
        {
          "type": "null"
        }
      ]
    },
    "age": {
      "anyOf": [
        {
          "type": "integer",
          "description": "User\'s age",
          "minimum": 0,
          "maximum": 120
        },
        {
          "type": "null"
        }
      ]
    }
  },
  "required": [
    "id",
    "name",
    "email",
    "role",
    "isActive",
    "tags",
    "age"
  ],
  "additionalProperties": false
}

How Constraints Map to JSON Schema

Ack attempts to map its built-in constraints to corresponding JSON Schema keywords:

Ack Constraint or Schema	JSON Schema Keyword	Notes
`minLength(n)`	`minLength: n`	String
`maxLength(n)`	`maxLength: n`	String
`matches(p)`	`pattern: p`	String
`email()`	`format: email`	String
`date()`	`format: date`	String
`datetime()`	`format: date-time`	String
`time()`	`format: time`	String
`uri()`	`format: uri`	String
`uuid()`	`format: uuid`	String
`ipv4()`	`format: ipv4`	String
`ipv6()`	`format: ipv6`	String
`enumString([...])`	`enum: [...]`	String
`min(n)`	`minimum: n`	Number (int/double)
`max(n)`	`maximum: n`	Number (int/double)
`greaterThan(n)`	`exclusiveMinimum: n`	Number (exclusive)
`lessThan(n)`	`exclusiveMaximum: n`	Number (exclusive)
`multipleOf(n)`	`multipleOf: n`	Number (int/double)
`minLength(n)`	`minItems: n`	List (array)
`maxLength(n)`	`maxItems: n`	List (array)
`unique()`	`uniqueItems: true`	List (array)
`nullable()`	`anyOf: [<schema>, {type: null}]`	Any schema
`withDefault(v)`	`default: v`	Any schema
`describe(d)`	`description: d`	Any schema
`Ack.integer`	`type: integer`	Type
`Ack.double`	`type: number`	Type
`Ack.string`	`type: string`	Type
`Ack.boolean`	`type: boolean`	Type
`Ack.list(...)`	`type: array`, `items: {...}`	Type
`Ack.object(...)`	`type: object`, `properties: {...}`, `required: [...]`	Type

Shape Stability Notes

toJsonSchema() uses stable nullability wrapping rules:

Primitive/object/list/enum schemas marked with .nullable() are emitted as:
- anyOf: [<base-schema>, { "type": "null" }]
Ack.anyOf([...]).nullable() is emitted as nested anyOf:
- outer anyOf for nullability
- inner anyOf for the union branches
Ack.discriminated(...).nullable() follows the same nested pattern:
- outer anyOf for nullability
- inner anyOf for discriminated branches

This means nullable enums are represented as:

{
  "anyOf": [
    { "type": "string", "enum": ["admin", "user", "guest"] },
    { "type": "null" }
  ]
}

And nullable discriminated unions are represented as:

{
  "anyOf": [
    { "anyOf": [/* discriminated object branches */] },
    { "type": "null" }
  ]
}

If you build consumers that inspect generated schemas, treat nullability and union composition as separate concerns and avoid assuming enum values always live at the top level.

Limitations:

Custom Constraints: Constraint<T> + Validator<T> instances added via .constrain() are not translated to JSON Schema as there's no standard way to represent arbitrary logic.
additionalProperties: Ack.object(..., additionalProperties: false) becomes additionalProperties: false; true becomes additionalProperties: {} (open object schema).

Integrating into API Documentation

You can use the generated JSON Schema map within a larger API documentation structure.

// Assume you have a function to build the full API spec
Map<String, dynamic> buildApiSpecification() {
  final userJsonSchema = userSchema.toJsonSchema();
  
  return {
    'schemas': {
      'User': userJsonSchema
    },
    'endpoints': {
      '/users': {
        'post': {
          'summary': 'Create a new user',
          'requestBody': {
            'required': true,
            'content': {
              'application/json': {
                // Reference the generated schema
                'schema': {
                  '\$ref': '#/schemas/User'
                }
              }
            }
          }
        }
      }
    }
  };
}

// Usage
final fullApiSpec = buildApiSpecification();
print(JsonEncoder.withIndent('  ').convert(fullApiSpec));

This allows you to maintain your validation logic and API documentation source in one place (your Ack schemas).

Advanced JSON Schema Features

Schema Descriptions and Metadata

Add descriptions and metadata to your schemas for better documentation:

final userSchema = Ack.object({
  'id': Ack.string().uuid().describe('Unique user identifier'),
  'name': Ack.string().minLength(1).describe('User\'s full name'),
  'email': Ack.string().email().describe('User\'s email address'),
  'age': Ack.integer().min(0).max(150).describe('User\'s age in years').optional(),
}).describe('Represents a user in the system');

final jsonSchema = userSchema.toJsonSchema();
// Generated schema will include description fields

Default Values in JSON Schema

Schemas with default values will include them in the generated JSON Schema:

final configSchema = Ack.object({
  'theme': Ack.enumValues(Theme.values).withDefault(Theme.light),
  'notifications': Ack.boolean().withDefault(true),
  'maxItems': Ack.integer().min(1).max(100).withDefault(10),
});

final jsonSchema = configSchema.toJsonSchema();
// Will include "default" properties in the JSON Schema

Complex Schema Patterns

JSON Schema generation works with all Ack schema types:

// Union types
final mixedValueSchema = Ack.anyOf([
  Ack.string(),
  Ack.integer(),
  Ack.boolean(),
]);

// Discriminated unions
final shapeSchema = Ack.discriminated(
  discriminatorKey: 'type',
  schemas: {
    'circle': Ack.object({
      'type': Ack.literal('circle'),
      'radius': Ack.double().positive(),
    }),
    'rectangle': Ack.object({
      'type': Ack.literal('rectangle'),
      'width': Ack.double().positive(),
      'height': Ack.double().positive(),
    }),
  },
);

// Nested arrays and objects
final complexSchema = Ack.object({
  'users': Ack.list(userSchema).minLength(1),
  'metadata': Ack.object({
    'version': Ack.string(),
    'tags': Ack.list(Ack.string()).unique(),
  }).optional(),
});

// All generate valid JSON Schema
final mixedJson = mixedValueSchema.toJsonSchema();
final shapeJson = shapeSchema.toJsonSchema();
final complexJson = complexSchema.toJsonSchema();

Getting Started

Core Concepts

Guides

Reference