Validator Middleware

The Validator Middleware is built-in middleware that gives you capability to validate the intent before it’s handled and the result after it’s handled.

You can use any library (such as Zod, Joi, ajv…) you want to validate the intent, as long as it returns a boolean.

Remember built-in middlewares are intent aware, therefore you can customize the behavior per intent using the key intents.

How to use it

As for any Middleware, you can use it by adding it to the bus instance.

Then for each intent you want to validate, you provide a function that will return true if the intent is valid, false otherwise. The same applies for the result, you provide a function that will return true if the result is valid, false otherwise.

If you provide a function that returns false, the middleware will throw an Error.

If you don’t provide a function for an intent, the middleware will assume the intent is valid and won’t validate it.

const queryBus = createQueryBus<QueryHandlerRegistry>();
queryBus.useValidatorMiddleware({
    intents: {
        myIntent: {
            input: myFunctionThatValidateTheIntent,
            output: myFunctionThatValidateTheResult,
        },
    },
});

Here is an example using the Zod library:

const createUserSchema = z.object({
    name: z.string(),
    email: z.string().email(),
});

const createUserOutputSchema = z.object({
    userId: z.string(),
});

queryBus.useValidatorMiddleware({
    intents: {
        createUser: {
            input: (message) => createUserSchema.safeParse(message).success,
            output: (result) => createUserOutputSchema.safeParse(result).success,
        },
    },
});

Added Stamps

The Validator Middleware is not adding any stamps.

Going further

Look at the code of the Validator Middleware