I am passing a variable $category to category__and, and it works unless $category = 0;

'category__and' => array(4) // works
'category__and' => array($category, 4) // works if category > 1
'category__and' => array(0, 4) // does not work.

I originally tried to just use cat, but if the post has cat 4 and NOT cat 6, it will still show it. This is why I went to category__and.

'cat' => '4,6' // will show a post with category 4 even if 6 isn't present

I could write a conditional to check the value of $category but that seems unnecessary and I think I'm overlooking something.

  • under what conditions would you end up with a category ID of 0? IDs start at 1, 0 can never be a valid category ID.
    – Milo
    Feb 4 '15 at 20:53
  • @Milo I wrote a post handler that has defaults set to 0. Would it better to have $category = '' as the default? Feb 4 '15 at 21:15
  • it would be better to just verify that it's a valid value before trying to do anything with it.
    – Milo
    Feb 4 '15 at 21:16
  • @Milo ah, I could create that array before running the query. that does work. good call :) Feb 4 '15 at 21:30
  • That is normal. You are saying "get me posts that are in category 0 and 4", so it works but you have not any post taht mathc the condition. Checking the value of $category before you use it on the query is the only way I can imagine.
    – cybmeta
    Feb 5 '15 at 9:25

You could use tax_query to solve this problem.

I assume 4 and 6 are only categories, so you'll probably need to construct the queries within the $tax_query array rather than declare it, but let us know if that is a problem. Just remember that relation => 'AND' must be included.

$tax_query = array(
    relation => 'AND',
        'taxonomy'          => 'category',
        'field'             => 'term_id',   // 'term_id' by default, so just here as an example
        'terms'             => $cat,
        'include_children'  => false,       // true by defualt
        'operator'          => 'IN'         // 'IN' by default, so just here as an example
        'taxonomy'          => 'category',
        'terms'             => $cat2,
        'include_children'  => false,       // true by defualt

Once you've set $tax_query up as you require, just add it to the query, along with any other arguments you desire, like so -

'tax_query' => $tax_query

Check out the Class Reference for WP_Query for more details - http://codex.wordpress.org/Class_Reference/WP_Query#Taxonomy_Parameters


The OP has suggested that $cat may actually contain multiple categories as opposed to just one, so the code below (untested) should allow for this while still using the `tax_query' parameter of the query.

/** Ensure that '$cat' is cast as an array */
if(!is_array($cat) && !empty($cat))
    $cat = explode(',', $cat);
/** Ensure that '$cat2' is cast as an array */
if(!is_array($cat2) && !empty($cat2))
    $cat2 = explode(',', $cat2);
/** Create a single array of all categories */  
$cats_array = $cat + $cat2

/** Create the '$tax_query' variable and cast it as an array */
$tax_query = array();

/** Add each category to the 'tax_query' */
if(!empty($cats_array)) : foreach($cats_array as $single_cat) :

        $tax_query[] = array(
            'taxonomy'          => 'category',
            'terms'             => $single_cat,
            'include_children'  => false,       // true by defualt

/** Check to see if there is more than one category within the 'tax_query' and if so set the relation to 'AND' */
if(count($tax_query) > 1)
    $tax_query['relation'] = 'AND';

The only thing to note here is that you should check if(!empty($tax_query)) before adding it to your query.

You can use this method for custom taxonomies as well.

  • I have two variables I'd have to pass into this - $cat and $cat2. I already wrote the conditional to check the $category value but if I get a chance I'll test this out, and definitely remember in the future. I've never thought about using tax query. thanks! Feb 5 '15 at 15:03
  • You're welcome. If it's only every $cat and $cat2 you can use the example as modified above. However if you have say an array of category ID's you can use a foreach loop to construct the tax_query.
    – David Gard
    Feb 5 '15 at 15:27
  • Yup, only ever 2. The problem though is $cat could technically be "1,2,3,5,6" so I would need to check it's properties and split into an array. This is sidetracking from the actual issue above though, which your solution does like solve. I feel bad that I may never test it because it currently works, but I know that when updates come I'll have to try this. Feb 5 '15 at 17:12
  • Ok, you can still use the method above if $cat contains a list of categories, as opposed to just one. I'll see if I get time today and update the answer (if not for you then for others in the future).
    – David Gard
    Feb 6 '15 at 9:50
  • I've now updated my answer to take in to account your comments.
    – David Gard
    Feb 6 '15 at 10:18

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