How To Fix PHP Error Using WordPress Function get_terms()

We’ll analyze a common PHP error that occurs when using the WordPress function get_terms() and explain how to resolve it. The error you’re encountering stems from passing incorrect arguments or misusing the data returned by the get_terms() function. Let’s dive into the issue, the cause of the error, and how to fix it with better practices.

Error Code:

You are setting a variable like this:

$args = array('parent' => 2818, 'hide_empty' => false);
$best_of_cat_child_terms = get_terms($args);
$best_of_cat = $best_of_cat_child_terms;

And you encounter the following PHP warning:

Warning:

argument supplied for foreach()

Location:
wp-includes/class-wp-term-query.php:373

Call Stack:

WP_Term_Query->get_terms()
wp-includes/class-wp-term-query.php:287
WP_Term_Query->query()
wp-includes/taxonomy.php:1217
get_terms()
wp-content/themes/theme-child/functions.php:26 (-> functions.php line 26 marked above)

Explanation of the Error:

The error message, “Invalid argument supplied for foreach()”, occurs when you attempt to loop through a variable that is not an array or an object that can be iterated over. In this case, you’re trying to use foreach() on $best_of_cat_child_terms — which is the result of the get_terms() function.

Why the Error Happens:

1. Incorrect Usage of get_terms(): The get_terms() function returns an array of terms, or an empty array if no terms are found. However, in some cases, it might return WP_Error instead of an array if something goes wrong in retrieving the terms.
2. Expecting an Array: You’re likely expecting $best_of_cat_child_terms to always be an array of terms, but the error suggests that the value returned is either null, an empty string, or a WP_Error object — none of which are valid to loop through with foreach().

How to Fix the Error:

To resolve this issue, you need to ensure that the result of get_terms() is an array before passing it to foreach(). You can add validation to check if the result is a valid array.

Updated Code:

Here’s an updated version of your code with added error checking:

$args = array(
    'parent' => 2818,
    'hide_empty' => false
);

// Get the child terms
$best_of_cat_child_terms = get_terms($args);

// Check if the result is an array and not a WP_Error
if (is_array($best_of_cat_child_terms) && !is_wp_error($best_of_cat_child_terms)) {
    $best_of_cat = $best_of_cat_child_terms;

    // Loop through the terms
    foreach ($best_of_cat as $term) {
        // Process each term here
        echo $term->name;
    }
} else {
    // Handle the case where get_terms() did not return a valid array
    echo "No terms found or an error occurred.";
}

Explanation of the Fix:

1. is_array($best_of_cat_child_terms): This checks whether the value returned by get_terms() is an array. If get_terms() fails, it might return a WP_Error object or null instead of an array, which causes the foreach() loop to fail.
2. !is_wp_error($best_of_cat_child_terms): This checks whether the result is not a WP_Error object. The get_terms() function may return a WP_Error if there is a problem with the query (e.g., invalid arguments, database issues, etc.).
3. foreach(): The loop runs only if $best_of_cat_child_terms is a valid array. If the check fails, it outputs an error message saying “No terms found or an error occurred.”

Additional Practice Functionality:

To improve your code further and handle edge cases, you can:

1. Validate Parent Term Existence: Before fetching terms, check if the parent term actually exists. This can help you avoid unnecessary queries for non-existent terms.
2. Default Fallback for Empty Results: If no terms are found, you might want to provide a default set of terms or handle the empty state gracefully.

Here’s an updated version with these features:

$args = array(
    'parent' => 2818,
    'hide_empty' => false
);

// Check if the parent term exists first
$parent_term = get_term(2818);
if (is_wp_error($parent_term)) {
    echo "Parent term not found.";
} else {
    // Get the child terms
    $best_of_cat_child_terms = get_terms($args);

    // Check if the result is an array and not a WP_Error
    if (is_array($best_of_cat_child_terms) && !is_wp_error($best_of_cat_child_terms)) {
        $best_of_cat = $best_of_cat_child_terms;

        // Loop through the terms
        foreach ($best_of_cat as $term) {
            // Process each term here
            echo $term->name . "<br>";
        }
    } else {
        // Handle the case where no child terms were found
        echo "No child terms found for the parent term.";
    }
}

Explanation of the Additional Features:

1. Parent Term Validation (get_term()): Before querying for child terms, we validate that the parent term exists. This prevents querying for child terms of a non-existent term.
2. Fallback for Empty Terms: Instead of just outputting a generic message when no terms are found, you could also consider showing alternative content or offering a default set of terms if appropriate.

Final Thoughts:

In WordPress, when working with get_terms(), it’s essential to check the return value before processing it. get_terms() might return a WP_Error or an empty array, and trying to loop through such results will cause issues. By validating the return value and checking for errors, you can avoid common pitfalls and ensure that your code runs smoothly.