Creating a required 1 out of 2 field schema, #3740

3pleFly · 2024-09-05T14:42:56Z

3pleFly
Sep 5, 2024

Hello

I wanna make a schema where at least 1 field is required. I know I can use refine but I think I can avoid it...
I've tried below a strategy but it's lacking. I've accomplished validating either one. But I am lacking a validation for when the user leaves BOTH empty. Any ideas?

The real complication is that the form consider null or empty string to be as EMPTY values. So, that's where I gotta pass these things through a truthy check to make sure there's a value in either one....

Would love some help :)


export const useCommentSchema = () => {
  return z.object({
    comment: z
      .string()
      .min(
        30,
        translate("General.Validations.MinCharacters").replace("X", "30")
      )
      .max(250, translate("General.Validations.MaxExceeded"))
      .regex(CommentBoxWithEnglish, translate("General.Validations.Regex")),
  });
};

export const useMyFileSchema = () => {
  return z.object({ file: useFileSchema(MAX_FILE_SIZE).nullable() });
};

export const useApplicationSchema = () => {
  return useCommentSchema()
    .merge(useMyFileSchema())  ////// This right has to check that both aren't empty. not empty string, not null.
    .or(useCommentSchema()) // Can do either this
    .or(useMyFileSchema()); // Or this
};

potatohoney-p · 2026-11-03T14:02:02Z

potatohoney-p
Nov 3, 2026

You can do this with a union, but each branch needs to describe both fields. In the original schema, useMyFileSchema() accepts { file: null }, so that branch lets both inputs be empty. The comment-only branch can also accept a valid comment while silently dropping an invalid file, because object schemas strip unknown keys.

Reuse the existing field validators and explicitly describe the empty values:

export const useApplicationSchema = () => {
  const comment = useCommentSchema().shape.comment;
  const file = useFileSchema(MAX_FILE_SIZE); // required file validator, no .nullable()
  const emptyComment = z.literal("").nullish(); // "", null, undefined, or omitted

  return z.union([
    z.object({
      comment,
      file: file.or(z.literal("")).nullish(),
    }),
    z.object({
      comment: emptyComment,
      file,
    }),
  ]);
};

The first branch requires a valid comment and allows a valid file or an empty file input. The second requires a valid file and an empty comment. Together they allow either field or both, while rejecting both-empty inputs. This assumes that a supplied, non-empty value must pass its own validator even when the other field is valid.

I tested this composition on Zod 3.25.76 and 4.6.7, Node 24.22.1. Your useFileSchema and regex implementations weren't included, so I used a bounded { name, size } object as the file validator and a string validator with min/max/regex checks. All 42 combinations per version passed, including:

comment: "", file: null → rejected.
Valid comment with file: "", null, or omitted → accepted.
Empty or omitted comment with a valid file → accepted.
Valid comment + invalid non-empty file → rejected.
Invalid non-empty comment + valid file → rejected.
Both valid → accepted, with both values retained in the parsed result.

Whitespace isn't treated as empty by this example. It keeps your existing comment validation and error messages. Union errors have a different structure from a single object schema, so check how your form resolver displays the branch errors.

Relevant docs: union evaluation, object key stripping, and nullish schemas.

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Creating a required 1 out of 2 field schema, #3740

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Creating a required 1 out of 2 field schema, #3740

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3pleFly Sep 5, 2024

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potatohoney-p Nov 3, 2026

3pleFly
Sep 5, 2024

potatohoney-p
Nov 3, 2026