set required_string on object after schema creation

[gruni1992]

Is it possible to set required_string after the schema has been created?

so instead of this:

const mySchema = z.object({someProperty: z.string()}, {required_string: 'this field is required'})

I would like to do something like this:

const mySchema = z.object({someProperty: z.string()})
const mySchemaWithCustomRequiredMessage = mySchema.withRequiredString('this field is required')

[dosubot[bot]]

Hi @gruni1992! I'm Dosu and I’m helping the zod team.

Zod doesn't support updating the required field error message (like required_string) after schema creation—there's no .withRequiredString() or similar method. Custom error messages for required fields must be set when you create the schema. If you need to customize error messages after creation, your options are to use a per-parse error map (by passing an error function to .parse() or .safeParse()) or set a global error map with z.config()—see the error customization docs for details.

Schema-level error messages always take precedence, so if you want a different required message, you'll need to recreate the schema with the new message. Zod schemas are intentionally immutable after creation, and this is by design. More on error precedence and customization here: error customization.

If you have a specific use case or need more tailored advice, let me know your Zod version. If this answers your question, feel free to close the issue!

To reply, just mention @dosu.

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[BrendanC23]

You can't specifically set the required_string property after defining a schema, but you can use refine to add an additional validation step and set a custom error message.

const mySchema = z.object({someProperty: z.string()})
const mySchemaWithCustomRequiredMessage = mySchema.refine((val) => val === "", { 
  error: "this field is required" 
});

[gruni1992]

I think this works on a string, but I actually want to make the whole object required, with a custom error message. In that case, it seems like it never even evaluates the refine stage, when the object is already null/undefined.

[gruni1992]

I just found a solution that works for me:

    supplierContact: z.object(supplierContactSchema.shape, {
      required_error: 'custom error',
    }).required(),