How to get next previous category in same taxonomy?

Question

Like WP get_adjacent_post function gives the next and previous post data based on the parameters i want to get the next/previous category data is there any WP built in function which does the right job or i have to write a custom query for that.

// Next/previous post example
$in_same_cat = false;
$excluded_categories = '';
$previous = true;
$previous_post = get_adjacent_post($in_same_cat,$excluded_categories,$previous);

i want next category by category slug or by category id

Any help would be appreciated

Answer 1

Is there any WP built in function which does the right job?

No.

[Do I] have to write a custom query for that?

No. Use get_terms(). Here is an example.

---

Add the wpse_99513_adjacent_category class to the functions.php theme file and call it like this:

$category_ids = new wpse_99513_adjacent_category( 'category', 'id', false );

-- 'category' is the taxonomy,
-- 'id' is the field to order the database query by and
-- false shows empty categories.

To get the next taxonomy use this:

$next_category = $category_ids->next( $category );

-- $category is the id of the category you are checking,
-- $next_category is set to false if there is an error and the next ID otherwise.

Previous works the same way:

$previous_category = $category_ids->previous( $category );

-- $category is the id of the category you are checking,
-- $previous_category is set to false if there is an error and the previous ID otherwise.

For slugs which skips empty categories use:

$category_ids = new wpse_99513_adjacent_category( 'category', 'slug' );

class wpse_99513_adjacent_category {

    public $sorted_taxonomies;

    /**
     * @param string Taxonomy name. Defaults to 'category'.
     * @param string Sort key. Defaults to 'id'.
     * @param boolean Whether to show empty (no posts) taxonomies.
     */
    public function __construct( $taxonomy = 'category', $order_by = 'id', $skip_empty = true ) {

        $this->sorted_taxonomies = get_terms(
            $taxonomy,
            array(
                'get'          => $skip_empty ? '' : 'all',
                'fields'       => 'ids',
                'hierarchical' => false,
                'order'        => 'ASC',
                'orderby'      => $order_by,
            )
        );
    }

    /**
     * @param int Taxonomy ID.
     * @return int|bool Next taxonomy ID or false if this ID is last one. False if this ID is not in the list.
     */
    public function next( $taxonomy_id ) {

        $current_index = array_search( $taxonomy_id, $this->sorted_taxonomies );

        if ( false !== $current_index && isset( $this->sorted_taxonomies[ $current_index + 1 ] ) )
            return $this->sorted_taxonomies[ $current_index + 1 ];

        return false;
    }

    /**
     * @param int Taxonomy ID.
     * @return int|bool Previous taxonomy ID or false if this ID is last one. False if this ID is not in the list.
     */
    public function previous( $taxonomy_id ) {

        $current_index = array_search( $taxonomy_id, $this->sorted_taxonomies );

        if ( false !== $current_index && isset( $this->sorted_taxonomies[ $current_index - 1 ] ) )
            return $this->sorted_taxonomies[ $current_index - 1 ];

        return false;
    }
}

Answer 2

This is what I came up with. Maybe not the best but works :)

Assuming we are on a custom taxonomy category page, and we want to go to the next

// get the term used on this current taxonomy page
$term = get_term_by( 'slug', get_query_var('term'), get_query_var('taxonomy') );

//set your arguments
$args = array(
     'hide_empty' => 0,
     'orderby' => 'name',
     'order' => 'DESC',
);

    //set your vars
$cycletaxonomy = 'author';
    // get all terms in a custom taxonomy

$cycleterms = get_terms($taxonomy, $args);

    // A for loop to cycle through all terms
for ($x=0; $x<count($cycleterms); $x++){
            // assign current cycled category slug - i could have used id too actually
    $thisslug = $cycleterms[$x]->slug;

    if ($curslug == $thisslug) {
        $nextslug = $cycleterms[$x+1]->slug;
        $prevslug = $cycleterms[$x-1]->slug;
        echo $nextslug;
        echo $prevslug;
                    // now do what you want with this slug - like putting it into a link tag
    }
};

Answer 3

I am not sure about bulit-in functions in WordPress but you can

Get Next and Previous Pages and than their category using next and previous post ID.

Answer 4

This is what i came up with a custom query solution hope it help others i wrote a custom function for this it works for all post type categories (post,custom post types)

function get_adjacent_category($category_slug,$taxonomy,$type){
    global $wpdb;
    if($type=="next"){
        $operater=" > ";
        $orderby=" ORDER BY tt.`term_id` ASC ";
    }else{
        $operater=" < ";
        $orderby=" ORDER BY tt.`term_id` DESC ";
    }
    $query="SELECT *,(SELECT `term_id` FROM wp_terms WHERE `slug`='".$category_slug."') AS given_term_id,
        (SELECT parent FROM wp_term_taxonomy WHERE `term_id`=given_term_id) AS parent_id
        FROM  `wp_terms` t
        INNER JOIN `wp_term_taxonomy` tt ON (`t`.`term_id` = `tt`.`term_id`)
        HAVING  tt.taxonomy='".$taxonomy."' AND tt.`parent`=parent_id AND tt.`term_id` $operater given_term_id $orderby LIMIT 1";
    return $wpdb->get_row($query);
}

$next_category =  get_adjacent_category($slug,$taxonomy,"next");
$previous_category =  get_adjacent_category($slug,$taxonomy,"previous");

Answer 5

Little update based on Akmur answer

$term = get_term_by('slug', get_query_var('term'), get_query_var('taxonomy'));
$curslug = $term->name;
$args = array(
    'hide_empty' => 0,
);
$cycletaxonomy = 'YOUR_TERM';
// get all terms in a custom taxonomy
$cycleterms = get_terms($taxonomy, $args);
// A for loop to cycle through all terms
for ($x = 0; $x < count($cycleterms); $x++) {
    // assign current cycled category slug - i could have used id too actually
    $thisslug = $cycleterms[$x]->name;

    if ($curslug == $thisslug) {
        $nextslug = $cycleterms[$x + 1]->name;
        $prevslug = $cycleterms[$x - 1]->name;
        echo '<ul class="post-nav">';
        if (!empty($nextslug)) {
            echo '<li class="next"><a href="' . get_term_link(intval($cycleterms[$x + 1]->term_id), 'YOUR_TERM') . '">' . $nextslug . '</a><li>';
        }
        if (!empty($prevslug)) {
            echo '<li class="previous"><a href="' . get_term_link(intval($cycleterms[$x - 1]->term_id), 'YOUR_TERM') . '">' . $prevslug . '</a><li>';
        }
        echo '</ul>';
        // now do what you want with this slug - like putting it into a link tag
    }
}

Answer 6

Place this function in your functions.php:

function adjacent_post_by_category( $category, $direction, $content ) {

    // Info
    $postIDs = array();
    $currentPost = get_the_ID();


    // Get posts based on category
    $postArray = get_posts( array(

        'category' => $category,
        'orderby'=>'post_date',
        'order'=> 'DESC'

    ) );


    // Get post IDs
    foreach ( $postArray as $thepost ):

        $postIDs[] = $thepost->ID;

    endforeach;


    // Get prev and next post ID
    $currentIndex = array_search( $currentPost, $postIDs );
    $prevID = $postIDs[ $currentIndex - 1 ];
    $nextID = $postIDs[ $currentIndex + 1 ];


    // Return information
    if( $direction == 'next' AND $nextID ):

        return '<a rel="next" href="' . get_permalink( $nextID ) . '">' . $content . '</a>';

    elseif( $direction == 'prev' AND $prevID ):

        return '<a rel="prev" href="' . get_permalink( $prevID ) . '">' . $content . '</a>';

    else:

        return false;

    endif;

}

And this as your prev/next links (function parameters are examples):

<?php echo adjacent_post_by_category( 10, 'prev', 'Show previous post' ); ?>

<?php echo adjacent_post_by_category( 10, 'next', 'Show next post' ); ?>