PHP Catchable fatal error: Object of class WP_Error could not be converted to string

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I need help with this:

PHP Catchable fatal error: Object of class WP_Error could not be
converted to string in
/hosting/www/ortopediairati.es/public/wp-content/themes/irati/rt-framework/functions/rt_breadcrumb.php
on line 58

I´ve updated to WordPress 4.8 and the web is not working well.

The full file is here:

<?php

/* RT-Breadcrumb Function */
function rt_breadcrumb(){
global $taxonomy,$term_slug,$post,$delimiter;

if(!get_option('rttheme_breadcrumb_menus')){
    return false;
}

//Markup 
$before="<div class="breadcrumb">".wpml_t(THEMESLUG, 'Breadcrumb Menu Text', get_option(THEMESLUG.'_breadcrumb_text')).' ';
$after="</div>";
$delimiter=" | ";

/*  WooCommerce Breadcrumb */ 
if ( function_exists( 'woocommerce_breadcrumb' ) ) {
    if( is_woocommerce() ){
        $defaults = array(
            'delimiter'  => $delimiter,
            'wrap_before'  => $before,
            'wrap_after' => $after,
            'before'   => '',
            'after'   => '',
            'home'    => null
        );

        woocommerce_breadcrumb($defaults); 
        return false;
    }
} 


echo $before;

//Home Page
echo "<a href=\"". BLOGURL ."\" title=\"". get_bloginfo('name')."\">".__( 'Home', 'rt_theme' )."</a>";

// page parents function
function page_parents($parent_page_id,$child_pages){
    global $delimiter;

    $parent_page = get_page($parent_page_id);
    $page_parents = $delimiter."<a href=\"".get_permalink($parent_page->ID)."\" title=\"". get_the_title($parent_page->ID) ."\" >". get_the_title($parent_page->ID) ."</a>" .$child_pages;

    if ($parent_page->post_parent) page_parents($parent_page->post_parent,$page_parents);

    else echo $page_parents;

}


// term parents function
function term_parents($term_id,$child_terms){
    global $taxonomy,$delimiter;

    $parent_term = get_term_by('ID',$term_id, $taxonomy);
    $term_parents = $delimiter."<a href=\"".get_term_link($parent_term->slug,$taxonomy)."\" title=\"". $parent_term->name ."\" >". $parent_term->name ."</a>" .$child_terms;

    if ($parent_term->parent) term_parents($parent_term -> parent,$term_parents);

    else echo $term_parents;

}

//get start page
function get_start_page($start_page){
    global $delimiter;

    //start page parents
    $get_start_page=get_page($start_page);
    if ($get_start_page -> post_parent){
        page_parents( $get_start_page -> post_parent,''); 
    }

    //start page
    if ($start_page && !get_query_var('lang')) {
        echo  $delimiter."<a href=\"".get_permalink($start_page)."\" title=\"". get_the_title($start_page) ."\" >". get_the_title($start_page) ."</a>";
    }
}

//terms
function term_links(){
    global $taxonomy,$post_type,$term_slug,$delimiter;

    //Find start page and define taxonomy names
    if($taxonomy=="product_categories"){
        $start_page=get_option('rttheme_product_list');
    }elseif($taxonomy=="portfolio_categories"){
        $start_page=get_option('rttheme_portf_page');
    }   

    //get start page
    if ($start_page) get_start_page($start_page);


    $term=get_term_by('slug',$term_slug, $taxonomy);

    //parent terms
    if (is_object($term) && $term -> parent){
        echo term_parents($term -> parent,'');   
    } 

    //current term
    if(is_object($term) && $term->slug) echo  $delimiter."<a href=\"".get_term_link($term->slug,$taxonomy)."\" title=\"". $term->name ."\" >". $term->name ."</a>";
}



//Pages
if ( is_page() ){
    //parent pages
    if ($post -> post_parent){
        page_parents( $post -> post_parent,''); 
    } 

    //current page
    echo  $delimiter ."". $post->post_title;
}

//Single
elseif (is_single() && !is_attachment()){ 
    // Get post type
    $post_type = get_post_type();

    //Taxonomies
    if($post_type == 'products' || $post_type == 'portfolio'){

        term_links();
        //current page
        echo  $delimiter."<a href=\"".get_permalink()."\" title=\"". get_the_title() ."\" >". get_the_title() ."</a>";

    }else{
    //Categories

    //start page
    $start_page=get_option('rttheme_blog_page');

    //get start page
    if ($start_page) get_start_page($start_page);

        $category_id = get_the_category();
        $category_id = $category_id[0]->cat_ID;//only one category can be show in the list  - the first one
        echo $delimiter;
        if($category_id){
            echo get_category_parents($category_id, TRUE, $delimiter, FALSE );
        }
        echo $post->post_title;
    }

//Category
}elseif (is_category()){
    //start page
    $start_page=get_option('rttheme_blog_page');

    //get start page
    if ($start_page) get_start_page($start_page);

        echo $delimiter."".get_category_parents(get_query_var('cat'), TRUE, $delimiter, FALSE);

//Taxonomy
}elseif (is_tax()){
    term_links();
} else {
    echo  $delimiter."";
    wp_title('');
}

echo $after;

wp_reset_query(); 
}
?>

Could someone help me?

1
1

Line 58 as the error indicates is this line:

$parent_term = get_term_by('ID',$term_id, $taxonomy);
$term_parents = $delimiter."<a href=\"".get_term_link($parent_term->slug,$taxonomy)."\" title=\"". $parent_term->name ."\" >". $parent_term->name ."</a>" .$child_terms;

And our error is:

Object of class WP_Error could not be converted to string

Which means that one of those things being appended is not a "string", but actually a WP_Error object.

I would cast suspicion on get_term_link, which is probably what’s returning the error object, which suggests either that the:

  • term doesn’t exist
  • the taxonomy isn’t registered or valid
  • the values being passed are unexpectedly blank
  • $parent_term isn’t a term, but an error object

Which leads us to the lesson here:

Sometimes functions return error objects and you have to check for that, don’t just assume it succeeded

How to Check for Errors

Lets take an example that will always fail:

$value = get_term_link( "not a real term","fake taxonomy" );
if ( is_wp_error( $value ) ) {
    // something went wrong
}

is_wp_error will be true if $value is an error object. Some functions may return false or null, so !empty( $value ) is also a useful check

Error objects can contain error codes and messages, and you can use the get_error_message() method to display them:

$value = get_term_link( "not a real term","fake taxonomy" );
if ( is_wp_error( $value ) ) {
    // something went wrong
    echo $value->get_error_message();
}

You could also set $value manually to a default value instead

A final note on globals

The code makes use of global variables, but these variables have super generic names such as $taxonomy. Other plugins may also use these, and they can clash. The same is true of function names.

Better

Prefix them:

// term parents function
function sergi_term_parents( $term_id, $child_terms ) {
    global $sergi_taxonomy, $sergi_delimiter;

Best

Use dependency injection and eliminate the globals entirely:

// term parents function
function sergi_term_parents( $term_id, $child_terms, $taxonomy, $delimeter ){

Now your term_parents function will never clash, and works for any taxonomy or delimeter

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