How to create a generic zod parser factory that gives a picked schema with types?

[zakia98]

Hi all,

I'm trying to create a generic zod parser factory that takes a schema and a list of fields that transforms that schema into a picked schema, but I am having an issue where the return type information is filtered out to any.

Here's what I have so far:

    const parseFactory = (schema: z.AnyZodObject) =>  { 
        return <T extends keyof z.infer<typeof schema>>({item, fields}: {item: unknown, fields: T[]}): Pick<z.infer<typeof schema>, T> | undefined=> {
          try {
            const pickedSchema = schema.pick(Object.fromEntries(fields.map(field => [field, true])))
            return pickedSchema.parse(item)
          } catch (error) {
            // error handling
          }
        }
    }

However, in the above, the type of the return is :

    {
        [x: string]: any;
        [x: number]: any;
    }

Any help would be appreciated!

[zakia98]

Sorry, just wondering if I could bump this?

[snigdha920]

I think the [x: string]: any; type is coming from the Object.fromEntries method, which does not type the keys of the object: https://github.com/microsoft/TypeScript/blob/8da951cbb629b648753454872df4e1754982aef1/src/lib/es2019.object.d.ts#L8

Related issue: microsoft/TypeScript#35745

Here's what works for me:

export type UserSchemaType = z.infer<typeof UserSchema>;

export function validateUserSchemaFields(
  fields: (keyof UserSchemaType)[],
  data: Partial<UserSchemaType>
) {
  try {
    UserSchema.pick(getMask(fields)).parse(data);
    return true;
  } catch {
    return false;
  }
}

function getMask<Schema extends z.AnyZodObject, Fields extends keyof z.TypeOf<Schema>>(arr: Fields[]) {
  return arr.reduce(
    (acc, item) => {
      acc[item] = true;
      return acc;
    },
    {} as { [k in Fields]?: true }
  );
}

This is not a factory because you can't pass the schema as a parameter, but once you have the schema this works.