Use API to update a "select" field

[nathan]

I have a page that has a field that contains a page.

How do I use the API to update a page select field in the page's page?

Example:

User page has field "member" which points to a member page.

Member page has field "gender" which points to page for selecting gender.

How do I change the page the gender points to from the user page?

I've tried 

$user->member->gender = 123;

 where 123 is the new page ID.

Also, 

$user->member->set("gender", 123);

Both of these seem not to work.

[adrian]

This works for me:

$user->of(false);
$user->member->gender = 123;
$user->member->save("gender");

EDIT: or for something even simpler using the new method introduced in 2.6.9 (https://processwire.com/blog/posts/processwire-2.6.9-core-updates-and-new-procache-version/#new-page-gt-setandsave-method):

$user->member->setAndSave('gender', 123);

[LostKobrakai]

As adrian's answer shows you'll need to save the member page, not the user. The user page just holds the reference to the member page, but the fielddata of both pages are fully unrelated to one another.

[nathan]

Ah yes, now it works.

I didn't realize you had to save the other page.

Thanks!