How to "group" (categorize) the Pages together?

Question

I have a lot of Pages which can be (need to be) grouped under a number of different Categories. ** Then the more important thing is, i need to control those pages (of different groups) programatically via functions.php.

Lets say, i would have:

• Page A (Categorized as: Fruits)
• Page B (Categorized as: Vehicles)
• Page C (Categorized as: Vehicles)
• Page D (Categorized as: Fruits)
• Page E (Categorized as: Technology)

Then from functions.php, there would be some logics, like:

• If Page is under Fruits Category, then echo "This is related to Fruits.";.
• If Page is under Vehicles Category, then echo "This is related to Vehicles.";.
• If Page is under Technology Category, then echo "This is related to Technologies.";.

I dont know this is about Taxonomy or Tagging or Custom Field or something. But:

• What is the ideal way to do it please? (Especially to be able to control from backend coding.)

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And again please let me repeat, "Pages". (Not about Posts or any other)

Answer 1

You can use categories with pages by registering the category taxonomy for the page object type:

function categories_for_pages(){
    register_taxonomy_for_object_type( 'category', 'page' );
}
add_action( 'init', 'categories_for_pages' );

If you want to use a separate taxonomy for this, you can register your own taxonomy for pages.

Answer 2

1. First thing you need to do is to enable categories for pages, quite simple:

   function enable_categories_for_pages() {
       register_taxonomy_for_object_type('category', 'page');  
   }
   add_action( 'init', 'enable_categories_for_pages' );
   

Note that in WordPress, categories are shared between different post types

2. To register the categories in advance:

   $wp_insert_category(array(
       'cat_name' => 'Fruit',
       'category_description' => 'My Fruit posts',
       'category_nicename' => 'Fruit'
   ));
   

3. You can add categories to posts programmatically:

   wp_set_post_categories($post->ID, get_cat_ID( 'Fruit' ));
   

4. When displaying the page (named in Wordpress $post):

   if ($post->post_type == 'page'){
       if (has_category( 'Fruits', $post)){
           echo "This is related to Fruits.";
       }
   }