How do I create a way for users to assign categories to a post from the frontend?

2 comments

1. I wanted to provide you with a few ideas but once I started I couldn’t stop myself and wrote this little plugin with an obscure name to get you started.

   <?php 
   /*
   Plugin Name: WPSE Crowded Cats
   Plugin URI: http://wordpress.stackexchange.com/questions/43419/how-do-i-create-a-way-for-users-to-assign-categories-to-a-post-from-the-frontend
   Description: Allow visitors to change categories of posts. Ready to use with custom taxonomies and post types. 
   Version: 0.1
   Author: WPSE
   Author URI: http://wordpress.stackexchange.com/users/2110/maugly
   License: GPL2
   */
   
   
   add_action('plugins_loaded','wpse_init_crowd_cats_class');
   function wpse_init_crowd_cats_class(){
       new WPSECrowdCatsClass();
   }
   
   
   class WPSECrowdCatsClass { 
   
       function __construct() {
   
           // APPEND THE FORM AUTOMATICALLY TO EVERY POST
           add_filter( 'the_content', array( $this,'append_form' ) );
   
           // TEMPLATE ACTION TAG TO BE USED IN THEME
           // Usage: do_action('wpse_crowd_cats_form');
           // Usage: do_action('wpse_crowd_cats_form', $post_id, $taxonomy );
           add_action( 'wpse_crowd_cats_form', array( $this,'wpse_crowd_cats_form' ), 10, 2 );
   
           // FORM PROCESSING
           add_action( 'template_redirect', array( $this,'process_request' ) );
   
       }
   
       function process_request(){
   
           // check submission
           if ( ! isset($_POST['crowd-cat-radio']) || ! is_array($_POST['crowd-cat-radio']) )
               return;
   
           //TODO: check nonce
   
           // sanitize and check the input
           $suggested_terms = array_map( 'absint', $_POST['crowd-cat-radio'] );
           $post_id = absint( $_POST['crowd-cats-pid'] );
           $tax = $_POST['crowd-cats-tax'];
           if ( ! taxonomy_exists($tax) )
               return;
   
           // Allow only existing terms. Not sure if this is needed.
           $args = array( 'hide_empty' => false );
           $args = apply_filters( 'mcc_allowed_terms_args', $args, $post_id, $tax );
           $args['fields'] = 'ids';
           $allowed_terms = get_terms( $tax, $args );
           foreach ( $suggested_terms as $key => $term_id )
               if ( ! in_array( $term_id, $allowed_terms ) )
                   unset( $suggested_terms[$key] );
   
           // Add terms to taxonomy
           $affected_terms = wp_set_object_terms( $post_id, $suggested_terms, $tax, false );
           update_term_cache($affected_terms);
           return $affected_terms;
   
       }
   
   
       function get_form( $post_id=null, $tax='category' ) {
   
           if ( is_null($post_id) || ! taxonomy_exists($tax) )
               return false;
   
           $args = array( 'hide_empty' => false );
           $args = apply_filters( 'mcc_get_terms_args', $args, $post_id, $tax );
           $all_terms = get_terms( $tax, $args );
   
           if ( ! $all_terms )
               return false;
   
           $post_terms = wp_get_object_terms( $post_id, $tax, array( 'fields' => 'ids' ) );
   
           $permalink = get_permalink( $post_id );
   
           $out = "<form id='crowd-cats' action='$permalink' method='POST' >
               <ul >";
   
           foreach ( $all_terms as $t ) :
   
               $checked = in_array( $t->term_id, $post_terms) ? 'checked' : '';
               $out .= "<li>
                           <input type='checkbox' id='crowd-cat-$t->term_id' name='crowd-cat-radio[]' value='$t->term_id' $checked /> 
                           <label for='crowd-cat-$t->term_id' >".esc_attr($t->name)."</label>
                        </li>";
   
           endforeach;
   
           $out .= "</ul>
                   <input type='submit' value='Submit' name='crowd-cats-submit'/>
                   <input type='hidden' value='".esc_attr($tax)."' name='crowd-cats-tax'/>
                   <input type='hidden' value='$post_id' name='crowd-cats-pid'/>";
   
           //TODO: set nonce
   
           $out .= "</form>";
   
           return $out;
   
       }
   
   
   
       function append_form($content){
   
           global $post;
   
           if ( 'post' != $post->post_type )
               return $content;
   
           $form = $this->get_form( $post->ID );
   
           if ( ! $form )
               return $content;
   
           return "$content n $form";
       }
   
   
       function wpse_crowd_cats_form( $post_id=null, $taxonomy='category' ) {
   
           if ( is_null($post_id) ) {
               global $post;
               $post_id = $post->ID;
           }
   
           echo $this->get_form( $post_id, $taxonomy );
       }
   
   
   } // end of class               
   ?>
   

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2. The approach I would use would be update post and using in_array to see if the category has already been added.

   global $post; //define global of post
   $category_array = $post->post_category;
   
   //check if the new category or item is in the array already:
   
   foreach($_POST['category_checkbox'] as $value){
   if(!in_array($value,$category_array)){//not in array yet, add it
   $new_category = get_cat_ID( $value ) ;//turn the name into category ID
   array_push($category_array,$new_category);
   }
   }
   //update the post
   wp_update_post( array($post->ID,$category_array) );
   

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