Schema Generator

> Generate a draft-07 JSON schema definitions from an example JSON document

!Coverage lines

Features

- Generate a draft-07 JSON schema definitions from an example JSON document
- Easy to use
- Supports string formats (with more to come)
- Can generate either a strict or liberal schema

Usage

Install Schema Generator

``bash
$ npm install --save @jsonhero/schema-generator
`

generateSchema takes either a JSON object/array or JSON stringified and returns a valid draft-07 JSON Schema

`js
const { generateSchema } = require("@jsonhero/schema-generator");

const exampleJSON = {
id: 1234,
name: "Eric",
image: {
url: "https://foo.com/image.png",
},
email: "eallam@icloud.com",
homepage: "http://github.com/ericallam",
createdAt: "2021-12-17T12:55:58.141Z",
tags: ["foo", "bar"],
isAdmin: true,
};

const schema = generateSchema(exampleJSON);

// Now validate the provided JSON using the generated schema using ajv
const Ajv = require("ajv");
const ajv = new Ajv();
const addFormats = require("ajv-formats");
addFormats(ajv);

const validate = ajv.compile(schema);
const valid = validate(exampleJSON); // valid == true
`

The Schema generated in the above example

`json
{
"$schema": "http://json-schema.org/draft-07/schema#",
"$id": "https://jsonhero.io/schemas/root.json",
"type": "object",
"properties": {
"id": {
"type": "number"
},
"name": {
"type": "string"
},
"image": {
"type": "object",
"properties": {
"url": {
"type": "string",
"format": "uri"
}
},
"required": [],
"additionalProperties": true
},
"email": {
"type": "string",
"format": "email"
},
"homepage": {
"type": "string",
"format": "uri"
},
"createdAt": {
"type": "string",
"format": "date-time"
},
"tags": {
"type": "array",
"items": {
"type": "string"
}
},
"friends": {
"type": "array",
"items": {
"type": "object",
"properties": {
"id": {
"type": "number"
},
"name": {
"type": "string"
}
},
"required": [],
"additionalProperties": true
}
},
"isAdmin": {
"type": "boolean"
}
},
"required": [],
"additionalProperties": true
}
`

By default all properties are optional and additionalProperties are allowed. You can set the strict option to true if you'd like a more restrictive schema

`js
const { generateSchema } = require("@jsonhero/schema-generator");

const exampleJSON = {
id: 1234,
name: "Eric",
image: {
url: "https://foo.com/image.png",
},
email: "eallam@icloud.com",
homepage: "http://github.com/ericallam",
createdAt: "2021-12-17T12:55:58.141Z",
tags: ["foo", "bar"],
isAdmin: true,
};

const schema = generateSchema(exampleJSON, { strict: true });

// Now validate the provided JSON using the generated schema using ajv
const Ajv = require("ajv");
const ajv = new Ajv();
const addFormats = require("ajv-formats");
addFormats(ajv);

const validate = ajv.compile(schema);
const valid = validate(exampleJSON); // valid == true
`

The Schema generated in the above example

`json
{
"$schema": "http://json-schema.org/draft-07/schema#",
"$id": "https://jsonhero.io/schemas/root.json",
"type": "object",
"properties": {
"id": {
"type": "number"
},
"name": {
"type": "string"
},
"image": {
"type": "object",
"properties": {
"url": {
"type": "string",
"format": "image"
}
},
"required": ["url"],
"additionalProperties": false
},
"email": {
"type": "string",
"format": "email"
},
"homepage": {
"type": "string",
"format": "uri"
},
"createdAt": {
"type": "string",
"format": "date-time"
},
"tags": {
"type": "array",
"items": {
"type": "string"
}
},
"friends": {
"type": "array",
"items": {
"type": "object",
"properties": {
"id": {
"type": "number"
},
"name": {
"type": "string"
}
},
"required": ["id", "name"],
"additionalProperties": false
}
},
"isAdmin": {
"type": "boolean"
}
},
"required": [
"id",
"name",
"image",
"email",
"homepage",
"createdAt",
"tags",
"friends",
"isAdmin"
],
"additionalProperties": false
}
`

Generate Schema currently supports a few string formats

- Strings that are URLs will have the uri format
- Strings that are Date/Times will have the date-time format
- Strings that are emails will have the email format

If you are using ajv to use the generated schema, make sure to use the ajv-formats package

`js
const addFormats = require("ajv-formats");
addFormats(ajv);
`

You can also set the baseURI of the schema (i.e. the top level $id property)

`js
const { generateSchema } = require("@jsonhero/schema-generator");

const exampleJSON = {
foo: "bar",
};

const schema = generateSchema(exampleJSON, {
baseURI: "https://example.com/schemas/root.json",
});
`

`json
{
"$schema": "http://json-schema.org/draft-07/schema#",
"$id": "https://example.com/schemas/root.json",
"type": "object",
"properties": {
"foo": {
"type": "string"
}
},
"required": [],
"additionalProperties": true
}
``

Roadmap

- [ ] Support more draft versions of JSON Schema
- [ ] Support JSON Type Definitions
- [ ] Support enums and constants
- [ ] Support more string formats (regex, ipv4, ipv6, hostname, JSONPointer, time, date, uuid)
- [ ] Add examples