Exception filters

Exception filters provide a means to transform exceptions thrown from microservice handlers into meaningful objects. For example, our rpcCreate method currently throws an error with a string but what happens when the UserService throws an error or possibly the ORM. This method could throw a number of different errors and the only means that calling method knows what happened is to parse the error string. That’s simply unacceptable, so let’s fix it.

Start with creating a new exception class. Notice that our microservice exception extends RpcException and does not pass a HTTP status code in the constructor. These are the only differences between microservice exceptions and normal Nest.js API exceptions.

export class RpcValidationException extends RpcException {
    constructor(public readonly validationErrors: ValidationError[]) {
        super('Validation failed');
    }
}

We can now change the rpcCreate method to throw this exception when the...