Automatically assign a category to all posts

Question

How to automatically add/assign a category to ALL posts?

For a blog with 1000 recipe posts, how would you automatically add a category called "recipe" to all posts? (Without replacing current categories already assigned to a post. In other words, each post will still retain categories already assigned such as "chicken" "pork" and "beef" categories).

I could manually tick/check off the "recipe" category in WordPress dashboard but I am looking for an alternative method, maybe some code I can put in functions.php ?

If there is a method that can achieve this...

Will this method add the category "recipe" to both new and old posts, or just new posts?

Also, if I already have some posts in the category "recipe"
will this method add the "recipe" category TWICE to the post,
therefore causing this post to appear twice in the category "recipe" ?

Answer 1

You can totally create a category, get its ID from URL or database by looking into it. Then create a function, use $wpdb, write the MySQL query as you see fit adding the ID that you just got from URL or database.

Here may be some information to help you: http://codex.wordpress.org/Class_Reference/wpdb

There are 3 or 4 tables that you want to look on your database:

wp_posts - looking for ID and post_type columns;

wp_terms - looking for term_id and name, to see which category's ID is your new one, 'recipe' on this case.

wp_term_taxonomy - looking for the term_id and the taxonomy, just to make sure you'll use a category.

and where all the magic happens:

wp_terms_relationship - where object_id, is your Post's ID, and term_taxonomy_id is the term_taxonomy_id from wp_term_taxonomy.

Careful: Do not assume that the term_id from wp_terms is the same term_taxonomy_id from wp_term_taxonomy. There is a column for each of these and it surely has a good reason for that.

What you want to do is insert here, wp_posts.object_id and wp_term_taxonomy.term_taxonomy_id.

---

You can run something like:

INSERT INTO wp_term_relationships (object_id, term_taxonomy_id) (SELECT DISTINCT ID, your_new_category_id FROM wp_posts WHERE post_type = "your_post_type")

Replacing:

your_new_category_id = by your new category term_taxonomy_id, from wp_term_taxonomy

your_post_type = between those quotes, the post_type, if wordpress defaults, replace by "post"

Eg, assuming your new category has taxonomy_id 7 and your posts are recipe_post:

INSERT IGNORE INTO wp_term_relationships (object_id, term_taxonomy_id) (SELECT DISTINCT ID, 7 FROM wp_posts WHERE post_type = "recipe_post")

---

"Yeah dude, but OP wants to run something in functions.php".

That's ok:

function update_categories(){
    global $wpdb;

    if ($_GET['updateall'] == 'banana'){
        echo "updating";
        $wpdb->query("INSERT IGNORE INTO wp_term_relationships (object_id, term_taxonomy_id) (SELECT DISTINCT ID, 7 FROM wp_posts WHERE post_type = 'recipe_post')");   
    }

}
add_action('wp_loaded', 'update_categories');

This will hook at everytime WordPress is loaded (usually each page), checking if you're sending a GETvalue equals to something that only you want to run, and want to run it once only. So replace 'banana' with something you see easy to remember and access: http://www.yourdomain.com/?updateall=banana

and done !

Of course, remove that hook and the function as soon as you end this update.

---

Your questions:

Will this method add the category "recipe" to both new and old posts, or just new posts?

Your call, if you want to select a range of posts, you may add more conditionals to WHERE like:

WHERE post_type = 'recipe_post' AND something = 'something something' AND date = 'some-good-date'

Also, if I already have some posts in the category "recipe" will this method add the "recipe" category TWICE to the post, therefore causing this post to appear twice in the category "recipe" ?

No, that's why IGNORE keyword is right after INSERT.

Answer 2

Check this out

http://wordpress-code-snippets.blogspot.in/2014/05/how-to-assing-category-to-post.html

Copy and Paste the Below code in you theme functions.php.

 function auto_add_category ($post_id = 0) {
 if (!$post_id) return;
 $tag_categories = array ( //  add multiple items as shown 'Tag Name' => 'Categroy Name'
   'toys' => 'Kids',
   'apple' => 'Fruits',
 );
 $post_tags = get_the_tags($post_id);
 foreach ($post_tags as $tag) {
   if ($tag_categories[$tag->name] ) {
     $cat_id = get_cat_ID($tag_categories[$tag->name]);
     if ($cat_id) {
       $result =  wp_set_post_terms( $post_id, $tags = $cat_id, $taxonomy = 'category', $append = true );
     }
   }
    }
  }
   add_action('publish_post','auto_add_category');
  ?>