openapi-ts-json-schema

openapi-ts-json-schema

Generate JSON schema TypeScript files (.ts) from OpenAPI definitions which can be natively used to infer types from (with json-schema-to-ts or fastify-type-provider-json-schema-to-ts).

Given an OpenAPI definition file, openapi-ts-json-schema will:

• Resolve external/remote $refs and dereference them with @apidevtools/json-schema-ref-parser
• Optionally inline, import or keep local $refs
• Convert to JSON schema with @openapi-contrib/openapi-schema-to-json-schema and openapi-jsonschema-parameters
• Generate one TypeScript JSON schema file for each definition (.ts files with as const assertion)
• Store schemas in a folder structure reflecting the original OpenAPI definition structure

Installation

npm i openapi-ts-json-schema -D

Usage

import { openapiToTsJsonSchema } from 'openapi-ts-json-schema';

const { outputPath } = await openapiToTsJsonSchema({
  openApiSchema: 'path/to/open-api-specs.yaml',
  definitionPathsToGenerateFrom: ['paths', 'components.schemas'],
});

...then in your code:

import Ajv from 'ajv';
import { FromSchema } from 'json-schema-to-ts';
import myModelSchema from 'path/to/schemas-autogenerated/components/schemas/MyModel.ts';

// Use generated JSON schemas as usual
const ajv = new Ajv();
const valid = ajv.validate(myModelSchema, { hello: 'World' });

// Use generated JSON schemas to infer model types from
type MyModel = FromSchema<typeof myModelSchema>;

Options

Property	Type	Description	Default
openApiSchema (required)	string	Path to the OpenApi file (supports yaml and json).	-
definitionPathsToGenerateFrom (required)	string[]	OpenApi definition object paths to generate the JSON schemas from. Only matching paths will be generated. (Supports dot notation: ["components.schemas"]).	-
refHandling	"inline" | "import" | "keep"	"inline": inline $ref schemas. "import": generate and import $ref schemas. "keep": keep $ref value.	"inline"
schemaPatcher	(params: { schema: JSONSchema }) => void	Dynamically patch generated JSON schemas. The provided function will be invoked against every single JSON schema node.	-
outputPath	string	Path where the generated schemas will be saved. Defaults to /schemas-autogenerated in same directory as provided openApiSchema.	-
plugins	ReturnType<Plugin>[]	A set of optional plugin to generate any extra custom. See plugins docs. output.	-
silent	boolean	Don't console.log user messages.	false

Notes

Generated JSON schema path names get escaped in order to be valid file system names.

Circular $refs can be technically resolved with "import" refHandling option. But TS will stop the type recursion and type the schema as any (error ts(7022)). See relevant tests.

Take a look at the Developer's notes for a few more in-depth explanations.

Return values

Beside generating the expected schema files under outputPath, openapiToTsJsonSchema returns the following data:

{
  // The path where the schemas are generated
  outputPath: string;
  metaData: {
    // Meta data of the generated schemas
    schemas: Map<
      // OpenAPI ref. Eg: "#/components/schemas/MySchema"
      string,
      {
        schemaId: string;
        // JSON schema Compound Schema Document `$id`
        schemaFileName: string;
        // Valid filename for given schema (without extension).
        schemaAbsoluteDirName: string;
        // Absolute path pointing to schema folder
        schemaAbsolutePath: string;
        // Absolute path pointing to schema file
        schemaAbsoluteImportPath: string;
        // Absolute import path (without extension)
        schemaUniqueName: string;
        // Unique JavaScript identifier used as import name
        schema: JSONSchema;
        // The actual JSON schema
        isRef: boolean;
        // True is schemas is used as a `$ref`
      }
    >;
  }
}

Plugins

Plugins are intended as a way to generate extra artifacts based on the same internal metadata created to generate the JSON schema output.

openapi-ts-json-schema currently ships with one plugin specifically designed to better integrate with Fastify, but you can write your own.

Read plugins documentation 📖.

Todo

• Consider merging "operation" and "path" parameters definition
• Consider removing required definitionPathsToGenerateFrom option in favour of exporting the whole OpenAPI definitions based on the structure defined in specs
• Consider adding a way to customize the values of the generated JSON schema ids. This could be beneficial even in case of multiple schemas being merged with plugins

Changelog

0.4.0

Minor Changes

• 905ef5a: Remove experimentalImportRefs option in favour of refHandling
• b5688ad: Expose metaData return property holding generated schemas meta data
• 79feb32: Introduce plugins option
• 85ca0e8: Add "keep" refHandling option, to preserve $ref objects
• 62ded69: Add fastifyIntegrationPlugin plugin

Patch Changes

• 9e0a222: Fix isRef meta data prop for inline refHandling option
• 27404ae: Fix external local $refs resolution