Breadcrumbs Support

[earthlingdavey]

Hi, this project looks interesting. Thanks for creating it.

I have a question. Let's say I have a page structure with these breadcrumbs:

Home > Post 1 > Post 2

There is an issue, where if I update the title of Post 1, and hit refresh on Post 2

the breadcrumbs are unchanged

Home > Post 1 > Post 2

I want it to show

Home > Post 1 renamed > Post 2

This is because an update to Post 1 doesn't invalidate Post 2's cache.

I looked into adding post:1 to post 2's flags with, millicache_flags_for_request. But that filter is called too early, and I can't see a practical way to programatically add these tags.

Is there a recommended way to do this? Ideally something robust that is a light touch to the codebase.

Could there be a function like millicache_add_flags_for_request, and I can run it in my breadcrumbs template, for each ID?

[ouun]

@earthlingdavey Do you mean that 'Post 2' is a child post of 'Post 1'? Do you use the hierarchy feature for pages here?

[earthlingdavey]

@ouun thanks a lot for your quick reply.

Yes, that's it - WordPress's post hierarchy. On Post 2, the parent is post is Post 1.

---

But, to add en extra degree of complexity, in my example, what if I edit the Home page, and change it's title to 'My Home'.

Now, the desired breadcrumbs on Post 2 would be

My Home > Post 1 > Post 2

but, in-fact, Post 2 cache would not be invalidated, and breadcrumbs would still read:

Home > Post 1 > Post 2

---

I see 1 solution, in the template files, allow developers to call a function like millicache_add_flags_for_request

//breadcrumbs.php

///..

// Add homepage to breadcrumb
// Add homepage to this page's flags with `millicache_add_flags_for_request`

// ..

// Add parent posts to breadcrumns
// Add parent posts to this page's flags with `millicache_add_flags_for_request`

---

Another potential solution, might be to hook into a low level function, so that MilliCache is aware of all the times the posts table is read.

It could extract the post ids, and add them to flags for the current post.

e.g.

• Post 2 is rendered (not from cache)
• MilliCache filter is triggered (IDK if there would be a suitable hook), and knows that Home and Post 1 titles have been accessed.
• Flags are added to Post 2, for the IDs of Home and Post 1.

---

There are probably other approaches, do you have something in mind that would work with the current release of MilliCache, or would this be a feature request?

[ouun]

Thank you so much, @earthlingdavey! This is exactly the kind of situation where one of MilliCache's main features shines: Rules.

It wouldn't make sense to bake a fix into MilliCache itself as that would purge every user's parent pages regardless of whether they actually mention the parent title (e.g. in a breadcrumb). In your case it's easy to solve with a custom rule.

Add the ancestor post: flag to children

The child depends on the parent, so the dependency belongs on the child's cache entry, declared only when the crumb is actually rendered. That's exactly the condition → action shape rules give you:

• Condition = "does this page render breadcrumbs?"
• Action = "tag it with its ancestors' post: flags."

Nothing is baked into core, nothing clears a parent that has no dependents, and it's fully opt-in per site.

millicache()->rules()->create( 'my-rule:breadcrumbs' )
    ->on( 'template_redirect', 25 )
    ->when()
        // Pick whatever identifies your crumb-bearing pages. These are AND-ed,
        // so use ->when_any() instead if you mean "either/or".
        ->is_singular()
        // In WP >6.9 there is a breadcrumbs block
        ->has_block( 'core/breadcrumbs' )
    ->then()
        ->custom( 'add-crumb-flags', function () {
            foreach ( get_post_ancestors( get_queried_object_id() ) as $ancestor_id ) {
                millicache()->flags()->add( 'post:' . $ancestor_id );
            }
        } )
    ->register();

Now the child additionally carries its parent's (and grandparent's) post: flag, so it gets cleared whenever the parent changes.

Also clearing crumb pages when the Home title changes

But, to add an extra degree of complexity, in my example, what if I edit the Home page and change its title to 'My Home'?

If Home is a static front page, just add one more dependency in the same action — the front-page post itself:

->custom( 'add-crumb-flags', function () {
    // Parent / grandparent crumbs
    foreach ( get_post_ancestors( get_queried_object_id() ) as $ancestor_id ) {
        millicache()->flags()->add( 'post:' . $ancestor_id );
    }

    // Home crumb → depend on the front-page post itself
    $front_id = (int) get_option( 'page_on_front' );
    if ( $front_id ) {
        millicache()->flags()->add( 'post:' . $front_id );
    }
} )

Now editing the front page clears post:{front_id}, which cascades to every page carrying the Home crumb.

One thing to note: because this rides on MilliCache's automatic post-update clearing, those pages are purged (rebuilt cold on the next request), not expired. That's perfectly fine for most sites. If you'd rather serve stale-while-revalidate during the rebuild, you'd flip it around to an invalidation-side rule that clears with expire = true on the relevant save hook instead. Happy to share that variant if it's useful.

There are many ways to solve this. You could also come from the other side and invalidate post:* (or a custom crumb:* flag) via a ->clear() action. So this is just one approach; what fits best depends on your setup.

A good starting point for working with Rules is in the MilliCache docs and you can deep-dive in the MilliRules docs, too.

[earthlingdavey]

Thank you for the details. This looks like the right approach for our setup.