A Small Zod Bug That Taught Me About Type Coercion

While working on FocusYar, my Next.js project, I had a confusing issue: a goal existed in the database, but the application couldn't retrieve it correctly.

The problem was a type mismatch.

I was working with an ID that arrived as a string, while my Zod schema expected a number.

Before

const id = "123";

The Fix

import { z } from "zod";

const schema = z.object({
  id: z.coerce.number(),
});

z.coerce.number() attempts to convert the input to a number before validation.

This is especially useful when handling URL parameters and query strings.

A More Strict Version

If the ID must be a positive integer, I can validate that requirement too:

const schema = z.object({
  id: z.coerce.number().int().positive(),
});

One important detail: coercion and validation are different things. Converting a value to a number doesn't automatically make it a valid ID.

My Takeaway

When debugging a problem, I shouldn't immediately assume the database or query is broken. I should inspect the data, check its type, and follow it through the application.

I'm learning to solve problems by understanding their causes instead of just fixing their symptoms.

typescript #zod #nextjs #beginners