1/*
  2This is what I entered into ChatGPT if you ever want to expand on this.
  3 
  4"How can I add three custom fields to Wordpress Posts without a Plugin.
  5 
  6The custom fields are Reading Time, Level, and Source.
  7 
  8The Reading Time field will be numeric.
  9The Level field will be a drop down field with the following entries; Basic, Intermediate, and Advanced.
 10The Source field is a text field."
 11 
 12*/
 13 
 14 
 15 
 16 
 17function add_custom_fields() {
 18    // Add custom field: Reading Time
 19    add_meta_box(
 20        'reading_time',                 // Unique ID
 21        'Reading Time',                 // Title
 22        'display_reading_time_callback', // Callback function to display the field
 23        'post',                         // Post type
 24        'normal',                       // Context
 25        'high'                          // Priority
 26    );
 27 
 28    // Add custom field: Level
 29    add_meta_box(
 30        'level',                        // Unique ID
 31        'Level',                        // Title
 32        'display_level_callback',       // Callback function to display the field
 33        'post',                         // Post type
 34        'normal',                       // Context
 35        'high'                          // Priority
 36    );
 37 
 38    // Add custom field: Source
 39    add_meta_box(
 40        'source',                       // Unique ID
 41        'Source',                       // Title
 42        'display_source_callback',      // Callback function to display the field
 43        'post',                         // Post type
 44        'normal',                       // Context
 45        'high'                          // Priority
 46    );
 47}
 48 
 49function display_reading_time_callback($post) {
 50    // Retrieve the current value of the field
 51    $reading_time = get_post_meta($post->ID, 'reading_time', true);
 52 
 53    // Output the field HTML
 54    echo '<label for="reading_time">Reading Time (minutes):</label>';
 55    echo '<input type="number" id="reading_time" name="reading_time" value="' . esc_attr($reading_time) . '" />';
 56}
 57 
 58function display_level_callback($post) {
 59    // Retrieve the current value of the field
 60    $level = get_post_meta($post->ID, 'level', true);
 61 
 62    // Output the field HTML
 63    echo '<label for="level">Level:</label>';
 64    echo '<select id="level" name="level">';
 65    echo '<option value="Basic" ' . selected($level, 'Basic', false) . '>Basic</option>';
 66    echo '<option value="Intermediate" ' . selected($level, 'Intermediate', false) . '>Intermediate</option>';
 67    echo '<option value="Advanced" ' . selected($level, 'Advanced', false) . '>Advanced</option>';
 68    echo '</select>';
 69}
 70 
 71function display_source_callback($post) {
 72    // Retrieve the current value of the field
 73    $source = get_post_meta($post->ID, 'source', true);
 74 
 75    // Output the field HTML
 76    echo '<label for="source">Source:</label>';
 77    echo '<input type="text" id="source" name="source" value="' . esc_attr($source) . '" />';
 78}
 79 
 80function save_custom_field_data($post_id) {
 81    // Save the custom field data: Reading Time
 82    if (isset($_POST['reading_time'])) {
 83        $reading_time = sanitize_text_field($_POST['reading_time']);
 84        update_post_meta($post_id, 'reading_time', $reading_time);
 85    }
 86 
 87    // Save the custom field data: Level
 88    if (isset($_POST['level'])) {
 89        $level = sanitize_text_field($_POST['level']);
 90        update_post_meta($post_id, 'level', $level);
 91    }
 92 
 93    // Save the custom field data: Source
 94    if (isset($_POST['source'])) {
 95        $source = sanitize_text_field($_POST['source']);
 96        update_post_meta($post_id, 'source', $source);
 97    }
 98}
 99 
100add_action('add_meta_boxes', 'add_custom_fields');
101add_action('save_post', 'save_custom_field_data');