This article demonstrates how to build a Drupal module enabling users to "like" posts using jQuery AJAX calls for asynchronous data saving.

Key Features:

• Asynchronous liking via jQuery AJAX.
• Database storage of likes (per user, per post).
• Real-time like count updates.
• Clear UI indicating like/unlike status.

Module Creation:

1. Create a likepost folder within your Drupal installation's sites/all/modules/custom directory.
2. Inside likepost, create likepost.info:

<code>name = likepost
description = Allows users to like Drupal posts.
core = 7.x</code>

3. Create likepost.module: (Initial hook_help implementation included below for completeness, but the core functionality is added later)

/**
 * @file
 * Main module file.
 */

/**
 * Implements hook_help().
 */
function likepost_help($path, $arg) {
  if ($path == 'admin/help#likepost') {
    $output = '<h3>' . t('About') . '</h3>';
    $output .= '<p>' . t('This module allows users to like posts in Drupal.') . '</p>';
    return $output;
  }
}

4. Create likepost.install to define the database schema:

<?php
/**
 * Implements hook_schema().
 */
function likepost_schema() {
  $schema['likepost_table_for_likes'] = array(
    'description' => t('Stores post likes.'),
    'fields' => array(
      'userid' => array(
        'type' => 'int',
        'not null' => TRUE,
        'default' => 0,
        'description' => t('User ID'),
      ),
      'nodeid' => array(
        'type' => 'int',
        'unsigned' => TRUE,
        'not null' => TRUE,
        'default' => 0,
        'description' => t('Node ID'),
      ),
    ),
    'primary key' => array('userid', 'nodeid'),
  );
  return $schema;
}

Install the module. The likepost_table_for_likes table will be created.

AJAX Handling (likepost.module):

Add the following functions to likepost.module:

/**
 * Implements hook_menu().
 */
function likepost_menu() {
  $items['likepost/like/%'] = array(
    'title' => 'Like',
    'page callback' => 'likepost_like',
    'page arguments' => array(2),
    'access arguments' => array('access content'),
    'type' => MENU_SUGGESTED_ITEM,
  );
  return $items;
}

function likepost_like($nodeid) {
  $nodeid = (int) $nodeid;
  global $user;

  $like = likepost_get_like($nodeid, $user->uid);

  if ($like) {
    db_delete('likepost_table_for_likes')
      ->condition('userid', $user->uid)
      ->condition('nodeid', $nodeid)
      ->execute();
    $like = 0;
  } else {
    db_insert('likepost_table_for_likes')
      ->fields(array(
        'userid' => $user->uid,
        'nodeid' => $nodeid,
      ))
      ->execute();
    $like = 1;
  }

  $total_count = likepost_get_total_like($nodeid);
  drupal_json_output(array(
    'like_status' => $like,
    'total_count' => $total_count,
  ));
}

function likepost_get_total_like($nid) {
  $total_count = db_query('SELECT COUNT(*) FROM {likepost_table_for_likes} WHERE nodeid = :nodeid', array(':nodeid' => $nid))->fetchField();
  return (int) $total_count;
}

function likepost_get_like($nodeid, $userid) {
  $like = db_query('SELECT COUNT(*) FROM {likepost_table_for_likes} WHERE nodeid = :nodeid AND userid = :userid', array(':nodeid' => $nodeid, ':userid' => $userid))->fetchField();
  return (int) $like;
}

Displaying the Like Button (likepost.module):

/**
 * Implements hook_node_view().
 */
function likepost_node_view($node, $view_mode) {
  if ($view_mode == 'full') {
    $node->content['likepost_display'] = array(
      '#markup' => display_like_post_details($node->nid),
      '#weight' => 100,
    );
    $node->content['#attached']['js'][] = array(
      'data' => drupal_get_path('module', 'likepost') . '/likepost.js',
    );
    $node->content['#attached']['css'][] = array(
      'data' => drupal_get_path('module', 'likepost') . '/likepost.css',
    );
  }
}

function display_like_post_details($nid) {
  global $user;
  $totalLike = likepost_get_total_like($nid);
  $hasCurrentUserLiked = likepost_get_like($nid, $user->uid);
  return theme('like_post', array(
    'nid' => $nid,
    'totalLike' => $totalLike,
    'hasCurrentUserLiked' => $hasCurrentUserLiked,
  ));
}

/**
 * Implements hook_theme().
 */
function likepost_theme() {
  $themes = array(
    'like_post' => array(
      'arguments' => array('nid', 'totalLike', 'hasCurrentUserLiked'),
    ),
  );
  return $themes;
}

function theme_like_post($arguments) {
  $nid = $arguments['nid'];
  $totalLike = $arguments['totalLike'];
  $hasCurrentUserLiked = $arguments['hasCurrentUserLiked'];
  global $base_url;
  $output = '<div>';
  $output .= 'Total number of likes on the post are ';
  $output .= '<div class="total_count">' . $totalLike . '</div>';
  $linkText = ($hasCurrentUserLiked == 0) ? 'Like' : 'Unlike';
  $output .= l($linkText, $base_url . '/likepost/like/' . $nid, array('attributes' => array('class' => 'like-link')));
  $output .= '</div>';
  return $output;
}

Styling (likepost.css):

.likepost {
  border-style: dotted;
  border-color: #98bf21;
  padding: 10px;
}

.total_count {
  font-weight: bold;
}

.like-link {
  color: red;
}

.like-link:hover {
  color: red;
}

jQuery (likepost.js):

jQuery(document).ready(function($) {
  $('a.like-link').click(function(e) {
    e.preventDefault();
    $.ajax({
      type: 'POST',
      url: this.href,
      dataType: 'json',
      success: function(data) {
        $('a.like-link').text(data.like_status ? 'Unlike' : 'Like');
        $('.total_count').text(data.total_count);
      },
    });
  });
});

Remember to clear Drupal's cache after making changes. This detailed explanation should allow for a more robust and understandable implementation of the liking module. The screenshots are placeholders; you'll see the actual module output in your Drupal site.

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