Troubleshooting WordPress Custom Meta Query Ordering

What is a Meta Query in WordPress?

A meta query in WordPress allows developers to filter WordPress content based on custom fields and metadata associated with posts, pages, or other WordPress objects. Meta queries are a powerful way to query content beyond the default content fields like title and content.

For example, a meta query could find all posts that have a certain author specified in a custom “post_author” field, or filter products on an ecommerce site based on details stored in post meta fields. Meta queries extend the basic capabilities of WP_Query and the query variables it accepts.

Meta queries allow passing an array of parameters to filter by specific metadata keys or values attached to content. Some key parts of a meta query array include:

• key – the meta key or custom field to filter by
• value – the meta value to match
• compare – comparison operator (Equals, Not Equals, Exists, etc)

Here is a basic example of using a meta query to find posts by an “author_name” custom field:

$query = new WP_Query(array(
    'meta_query' => array(
        array(
            'key' => 'author_name',
            'value' => 'John Smith',        
        )
    )
));

Problems with Meta Query Ordering

The order that meta queries are defined in the array matters greatly in terms of the filtering logic used. But the default handling of meta query ordering in WordPress can lead to unexpected results if not properly understood.

By default, nested meta queries use an “AND” relation to combine their logic. So all nested queries and conditions must match for a post to be included in results. However, this means query order dictates the logic flow.

For example, consider this meta query with improper order:

$query = new WP_Query(array(
  'meta_query' => array(
     array(
        'key' => 'color',
        'value' => 'blue',
     ),
     array(
        'key' => 'size',
        'value' => 'large',
     ),
  ),        
));

Logically, this query intends to find posts where the color is blue OR the size is large. However, due to the default AND relation, these nested conditions are evaluated as:

color = blue AND size = large

As you can see, the ordering incorrectly requires posts to match both conditions, rather than matching either condition as intended.

Controlling Meta Query Ordering

Luckily, the relation parameter provides control over default ordering and logic flow of meta queries in WordPress.

The supported values for relation are:

• AND – All conditions must be met (default). Order matters.
• OR – Only one condition needs to match. Order does not matter.

So for example, we can fix the ordering of our example query by setting relation to OR:

$query = new WP_Query(array(
  'meta_query' => array(
     'relation' => 'OR',
     array(
        'key' => 'color',
        'value' => 'blue',
     ),
     array(
        'key' => 'size',
        'value' => 'large',
     ),
  ),  
)); 

Now results will contain posts where either the color OR size condition matches, fixing our query logic.

Troubleshooting Workflow

When dealing with issues around custom meta query logic and ordering, there is a solid workflow to identify and diagnose issues:

1. Examine the raw meta query array – Check if ordering looks correct for the intended logic flow.
2. Check relation parameters – See if AND vs OR is set properly based on order needs.
3. Print full queries – Use print_r($query) to output full query details and ensure proper syntax.
4. Try reorder queries – Experiment with different query structures to compare output/behavior.

Tools like Query Monitor and Debug Bar can also help view the constructed database queries and measure performance.

Pay particular attention to any warnings or errors shown – WP_Query will often reveal issues with bad meta query syntax preventing expected filter behavior.

Fixing Meta Query Ordering

When facing incorrect results due to meta query order, the main solutions are:

1. Reorganize Order – Rearrange queries for correct AND/OR logic as needed.
2. Update Relation Parameter – Change to OR if order should not matter.
3. Nest Queries – For more complex logic, break queries into nested chunks.

For example, we could fix the earlier incorrect query by either swapping the order:

  
 
$query = new WP_Query(array(
  'meta_query' => array(
     array(
        'key' => 'size',
        'value' => 'large',
     ),
    array(
       'key' => 'color',
       'value' => 'blue',
     ),
 )));

Or by introducing relation OR and leaving order intact:

$query = new WP_Query(array(
  'meta_query' => array(
     'relation' => 'OR',
     array(
        'key' => 'color',
        'value' => 'blue',
     ),  
     array(
        'key' => 'size',
        'value' => 'large',
     ),
 )));
 

With complex logic, nested queries may be needed:

 
$query = new WP_Query(array(
   'meta_query' => array(
      'relation' => 'OR',
        array(
           'key' => 'color',
           'value' => 'blue'
        ),
	array(
	   'relation' => 'AND',  
           array(
              'key'   => 'size',
              'value' => 'large',
	   ),
	   array(
              'key' 	 => 'brand',
	      'value' => 'Acme',
	   )
        ),
    ),    
));

Hopefully these examples give a solid grasp on methods for controlling meta query logic flow in WordPress queries!