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AJV dependency injection in getHandler feature

Why?​

Before version 0.27.0, for runtime validation purposes, the getHandler feature used an AJV instance created in the serverless-contracts package. However, some users reported that they needed to customize the AJV instance used for validation, for example to add custom keywords. Thus, we decided to add an ajv key to the getHandler signature to allow that and remove the default AJV instance, which introduced a breaking change.

For more context, check out:

How?​

Migrating from the default AJV instance to a custom one is quite straightforward:

  1. Upgrade @swarmion/serverless-contracts to version 0.26.0 or higher
  2. In your backend services handlers defined with the getHandler feature, update the signature of your implementation to provide an AJV instance:
+ import { AJV } from 'ajv';
+ const ajv = new AJV(); // or any other AJV instance you want to use

- const handler = getHandler(contract)(async (event) => {
+ const handler = getHandler(contract, { ajv })(async (event) => {
});

Share a singleton AJV instance across the whole project​

In order to reduce code duplication, we recommend creating a singleton AJV instance and share it across the whole project.

Here is an example of how to do it:

libs/ajv.ts
import Ajv from 'ajv';

export const ajv = new Ajv();

// or if using json-schema-faker

export const ajv = new Ajv({ keywords: ['faker'] });
functions/myFunction/handler.ts
import { getHandler } from '@swarmion/serverless-contracts';

import { myContract } from '@my-swarmion-app/contracts';

import { ajv } from 'libs/ajv';

export const handler = getHandler(myContract, { ajv })(async event => {
  // ...
});