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Transformers ​

JSON is the most commonly used data format in REST APIs. However, it does not map well to complex data types. For example, both regular strings and date strings become simple strings in JSON.

One approach to this problem is using a JSON superset. For most people, switching formats is not feasible. That's why we provide the @hey-api/transformers plugin.

WARNING

Transformers currently handle only the most common use cases. If your data isn't being transformed as expected, we encourage you to leave feedback on GitHub.

Considerations ​

Before deciding whether transformers are right for you, let's explain how they work. Transformers generate a runtime file, therefore they impact the bundle size. We generate a single transformer per operation response for the most efficient result, just like a human engineer would.

Limitations ​

Transformers handle only the most common scenarios. Some of the known limitations are:

  • union types are not transformed (e.g. if you have multiple possible response shapes)
  • only types defined through $ref are transformed
  • error responses are not transformed

If your data isn't being transformed as expected, we encourage you to leave feedback on GitHub.

Configuration ​

To generate transformers, add @hey-api/transformers to your plugins.

js
import { defaultPlugins } from '@hey-api/openapi-ts';

export default {
  client: '@hey-api/client-fetch',
  input: 'path/to/openapi.json',
  output: 'src/client',
  plugins: [
    ...defaultPlugins,
    '@hey-api/transformers', 
  ],
};

SDKs ​

To automatically transform response data in your SDKs, set transformer to true.

js
import { defaultPlugins } from '@hey-api/openapi-ts';

export default {
  client: '@hey-api/client-fetch',
  input: 'path/to/openapi.json',
  output: 'src/client',
  plugins: [
    ...defaultPlugins,
    '@hey-api/transformers',
    {
      name: '@hey-api/sdk', 
      transformer: true, 
    },
  ],
};

Dates ​

To convert date strings into Date objects, use the dates configuration option.

js
import { defaultPlugins } from '@hey-api/openapi-ts';

export default {
  client: '@hey-api/client-fetch',
  input: 'path/to/openapi.json',
  output: 'src/client',
  plugins: [
    ...defaultPlugins,
    {
      dates: true, 
      name: '@hey-api/transformers',
    },
  ],
};

This will generate types that use Date instead of string and appropriate transformers. Note that third-party date packages are not supported at the moment.

Example ​

A generated response transformer might look something like this. Please note the example has been edited for brevity.

ts
import type { GetFooResponse } from './types.gen';

const quxSchemaResponseTransformer = (data: any) => {
  if (data.baz) {
    data.baz = new Date(data.baz);
  }
  return data;
};

const bazSchemaResponseTransformer = (data: any) => {
  data = quxSchemaResponseTransformer(data);
  data.bar = new Date(data.bar);
  return data;
};

export const getFooResponseTransformer = async (
  data: any,
): Promise<GetFooResponse> => {
  data = bazSchemaResponseTransformer(data);
  return data;
};
ts
export type Baz = Qux & {
  id: 'Baz';
} & {
  foo: number;
  bar: Date;
  baz: 'foo' | 'bar' | 'baz';
  qux: number;
};

export type Qux = {
  foo: number;
  bar: number;
  baz?: Date;
  id: string;
};

export type GetFooResponse = Baz;

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