Question

136

Zod Schema: How to make a field optional OR have a minimum string contraint?

rated 0 times [ 141] [ 5] / answers: 1 / hits: 15961 / 2 Years ago, fri, september 2, 2022, 12:00:00

I have a field where I want the value to either be optional OR have the field have a minimum length of 4.

I've tried the following:

export const SocialsSchema = z.object({

  myField: z.optional(z.string().min(4, "Please enter a valid value")),

});

This passes if I used a value like: "good", but if I've got an empty value then it fails.

How do I correctly implement a constraint using zod schemas to make an optional value with a minimum constraint if the value is not empty?

Is it possible to do this without using regex or a regex solution the only way?

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markusdamienn

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1 Year ago

answered 2 Years ago daja · Accepted Answer

In your case, you consider "" to be the same as undefined (i.e.: when the string is empty, it's like there's no string at all).

It's implementable in Zod this way:

import { z } from "zod";

import { strict as assert } from "node:assert";



// `myString` is a string that can be either optional (undefined or missing),

// empty, or min 4

const myString = z

  .union([z.string().length(0), z.string().min(4)])

  .optional()

  .transform(e => e === "" ? undefined : e);



const schema = z.object({ test: myString });



assert( schema.parse({}).test === undefined ); // missing string

assert( schema.parse({ test: undefined }).test === undefined ); // string is undefined

assert( schema.parse({ test: "" }).test === undefined ); // string is empty

assert( schema.parse({ test: "1234" }).test === "1234" ); // string is min 4



// these successfully fail

assert( schema.safeParse({ test: "123" }).success !== true );

assert( schema.safeParse({ test: 3.14 }).success !== true );