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Nested object in Joi schema

I’ve defined validation schema via Joi with nested object in AWS value:

const schema = Joi.object({
  NODE_ENV: Joi.string()
    .valid('development', 'production', 'test')
  PORT: Joi.number().default(3000),
  AWS: Joi.object({
    accessKeyId: Joi.string().required(),
    secretAccessKey: Joi.string().required(),
    region: Joi.string().required(),
    bucket: Joi.string().required(),

Then I put my schema to config module

  imports: [
      isGlobal: true,
      validationSchema: schema,
      validationOptions: {
        abortEarly: false,
        cache: false,
  controllers: [AppController],
  providers: [AppService],
export class AppModule {}

I’ve added inside .env file the next value for AWS variable:

AWS={"region": "string", "accessKeyId":"string", "secretAccessKey": "string", "bucket": "string"}

but I got the next error message after starting nest:

> [email protected] start /Volumes/MacDATA/NestJs/project-8v
> nest start

                throw new Error(`Config validation error: ${error.message}`);
Error: Config validation error: "AWS" must be of type object

typeof process.env.AWS returns a string and Joi doesn’t understand that he should parse it, maybe I need to add some in validationOptions or I miss something. How can I solve it?


As of Joi v16.0.0, object and array string coercion is no longer available as a built-in option.

You can replicate this functionality by extending Joi. For example:

const JoiCustom = Joi.extend({
  type: 'object',
  base: Joi.object(),
  coerce: {
    from: 'string',
    method(value) {
      if (value[0] !== '{' && !/^s*{/.test(value)) {
        return {
      try {
        return { value: JSON.parse(value) };
      } catch (error) {
        return {
          errors: [error]

Then use JoiCustom in your schema:

const schema = Joi.object({
    AWS: JoiCustom.object({