Add Validation Rule Depending On Another Schema Value

[knoefel]

I have 2 select fields, the first field lets the user select a group and the second one a subgroup for that selected group.

The validation logic is that it is not guaranteed that a group will have subgroups. So if the user selects a group which won't contain any subgroups there shouldn't be any validation error. If on the other hand the user selects a group which has subgroups the validation rules should change that it is required to select a subgroup.

So what i need is a way to add the required rule to the subGroupSchema depending on the value of the groupSchema. Here is my schema:

const subGroupSchema = z.object({
  id: z.string(),
  name: translationSchema,
});

const groupSchema = z.object(
  {
    id: z.string(),
    name: translationSchema,
    subgroups: z.array(subGroupSchema),
  },
  { errorMap: (issue, ctx) => ({ message: isNil(ctx.data) ? 'core:form.validation.required' : ctx.defaultError }) }
);

export const schema = z.object(
  {
    skill: skillSchema,
    group: groupSchema,
    subGroup: subGroupSchema,
    level: z.number().min(1).max(5),
  }
);

I tried setting an errorMap on the schema object but without any luck as also need to place the error message on the subGroupSchema object.

Is this use case possible while using zod? Thx in advance for any tipp or help!!

[StefanTerdell]

It's a little verbose, but this works and keeps the type inference intact

const subGroupSchema = z.object({
  id: z.string(),
  name: translationSchema,
});

const groupBase = z.object(
  {
    id: z.string(),
    name: translationSchema,
  },
  {
    errorMap: (issue, ctx) => ({
      message: isNil(ctx.data)
        ? "core:form.validation.required"
        : ctx.defaultError,
    }),
  }
);

const groupWithSubgroupsSchema = groupBase.merge(
  z.object({
    subgroups: z.array(subGroupSchema),
  })
);

const groupWithoutSubgroupsSchema = groupBase.merge(
  z.object({
    subgroups: z.null(), // you could also use z.array(z.never()), z.undefined() or simply reuse the base schema for this variant
  })
);

const schemaBase = z.object({
  skill: skillSchema,
  level: z.number().min(1).max(5),
});

export const schema = z.union([
  schemaBase.merge(
    z.object({
      group: groupWithSubgroupsSchema,
      subGroup: subGroupSchema,
    })
  ),
  schemaBase.merge(
    z.object({
      group: groupWithoutSubgroupsSchema,
      subGroup: z.null(), //Once again, use whatever fits here
    })
  ),
]);