How To Retrieve Posts with Multiple Taxonomies

Get Posts with Multiple Taxonomies

I think that one of the more underestimated aspects of building solutions with WordPress comes with leveraging custom post types and custom taxonomies.

For those who are currently building products for others – be it plugins, custom themes, or web applications – then you’re likely familiar with how powerful these two features can be.

Specifically, if you’re used to the ideas of models and views, or data objects and a presentation layer (or whatever language your framework of choice uses to describe this information), you can think of custom post types as a bit of a hybrid of models and views.

Similarly, you can think of taxonomies as an easy way to stamp your data – in WordPress, we think of these as categories and tags – but sometimes, I think the terminology may limit us in thinking how we can leverage the features.

Nonetheless, if you’re used to working with WordPress, custom post types, and custom taxonomies, then you’ve likely faced a time when you’ve needed to query information based on a combination of the two.

And though there are a variety of different ways to retrieve custom post types and how they are tagged, here’s one way to grab information that’s stamped with multiple taxonomies.

Get Posts with Multiple Taxonomies

I’ll share more about this particular strategy at the end of the article, but suffice it to say that the general use case behind this is as follows:

  • You have a custom post type, say acme_post_type
  • You’re attempting to retrieve all of the posts of acme_post_type that are stamped with both dangerous and toxic.
  • Let’s say that each of these terms have the ID of 100 and 200, respectively.

To do this, you’ll need to understand two things:

  1. tax_query
  2. The relation argument for taxonomies.

The Codex has a lot of information on this, and in future posts, I’ll likely talk a bit more about this, but in order to actually perform this, you need the following information:

  • The custom post type ID (in our case, acme_post_type)
  • The various IDs of the custom taxonomy term – in our case, acme_labels – that you want to retrieve (in our case 100 and 200).

At this point, it’s a simple matter of basically filling in the information for this query. See the following gist:

Looks easy enough, right?

But for those of you who are new to custom post types, custom taxonomies, and/or custom queries, there are some key things to understand.

Getting The Gist

When it comes to writing code – be it application-level code, database queries, or whatever – I don’t ever think it’s safe to assume that the code makes sense (after all, it is called “code,” right? :).

And although people who have been writing code for quite a while may have an easier time deciphering what’s going on, that’s not always the case especially if this is your first foray into programming or into a new area of a platform or framework.

So, here’s an attempt to break down the above code into plain English:

  • The main query is made up of an associative array that consists of the custom post followed by a second array which is identified by the tax_query ID which contains a value of an array of arrays.
  • The tax_query array (or, technically, array of arrays) consists of three arguments: the relationship between the taxonomies being specified, and the terms themselves.
  • Because we’re looking for a custom post type that’s stamped with two taxonomy terms, we specify AND. If we wanted posts that were tagged with one or the either, then we could specified OR. Make sense? There are other operators, as well.
  • Next, we provide two arrays – one for each of our custom taxonomy term. Each array consists of three arguments: the ID of the custom taxonomy term (such as acme_labels, which field – or attribute – on which we’re querying, which is the term_ID, and the value for the term which is 100 and 200.

An attempt to make it even simpler: We’re instructing WordPress to get all of the acme_post_type posts that are stamped with both dangerous and the toxic.

From this point, you’d then perform the normal Loop operations to check to see if posts exist, and, if so, then iterate through them and render the information to the screen.

Again, there are endless ways in which data can be stored, represented, and stamped using custom post types and taxonomies, and this is but one way to retrieve posts that are stamped with two taxonomies.

There is much more than can be done with these two features that I’ll likely cover in future posts.

9 Replies to “How To Retrieve Posts with Multiple Taxonomies”

  1. Thank you for this…I have been (slowly) learning a lot from your tutorials as I am pretty much a beginner with the php side of things. I notice in several instances where you use the word “taxonomy” e.g. “Because we’re looking for a custom post type that’s stamped with two taxonomies…” Did you really mean “terms”?

    1. Ah, yes. This is a mistake that came from a lack of sleep and drafting a post when I should’ve been, y’know, catching up on said sleep. The post has been updated.

      Thanks for pointing those out ;).

  2. Hi Tom,

    thanks for a great tutorial. You explained how to show posts with both of taxonomies or terms selected – but what if you want to filter result just by taxonomy-one, or by taxonomy-two, or by taxonomy-one and taxonomy-two?

    1. As of now – and this may change in WordPress 4.3, though I can’t be certain – you’d have to execute separate queries. Kind of a pain, I know, and I may be totally wrong, but that’s what I can recall off the top of my head at the moment.

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