SQL Query Modification

To ensure privacy at the database level, this plugin hooks into the WordPress comment retrieval process. Instead of filtering results after they are fetched from the database, it modifies the underlying SQL query to ensure that unauthorized comments are never returned in the result set.

The `comments_clauses` Filter

The plugin utilizes the comments_clauses filter, which intercepts the parts of the SQL query (JOIN, WHERE, GROUP BY, ORDER BY, etc.) before it is executed by WP_Comment_Query.

By modifying the where clause, the plugin injects conditional logic that checks the relationship between the current user and the comment.

Permission Logic

The SQL modification applies different visibility rules based on the current user's role and identity:

Administrators: If the user has the manage_options capability, the query remains unmodified, allowing them to see all comments.
Post Authors: The query is modified to include comments where the comment_post_ID belongs to a post authored by the current user.
Comment Authors: The query is modified to include comments where the user_id matches the current logged-in user's ID.
Logged-out Users: The query is modified to return zero results, as there is no user_id to match.

Impact on Developer Functions

Because the modification happens at the comments_clauses level, it automatically affects standard WordPress template tags and functions. You do not need to update your theme files. The following functions will respect the privacy restrictions:

get_comments()
wp_list_comments()
WP_Comment_Query

Technical Example

When a non-administrator (User ID: 42) views a post, the plugin appends a condition to the WHERE clause of the SQL query. The resulting query structure looks similar to the following:

SELECT * FROM wp_comments 
WHERE (comment_approved = '1') 
AND (
    user_id = 42                                -- The user's own comments
    OR comment_post_ID IN (                     -- Comments on the user's posts
        SELECT ID FROM wp_posts WHERE post_author = 42
    )
)
ORDER BY comment_date_gmt DESC

Compatibility and Bypassing

While the plugin handles standard WordPress queries, it is important to note:

Internal Scope: The filtering logic is handled internally by the filter_comments_by_privacy method. While this is an internal implementation detail, it is triggered globally across the site once the plugin is active.
Bypassing Restrictions: If you are a developer and need to fetch all comments regardless of the plugin's restrictions (e.g., for a custom dashboard widget), you can temporarily remove the filter before running your query:

// Remove the privacy filter
remove_filter('comments_clauses', ['WP_Private_Comments', 'filter_comments_by_privacy']);

// Execute your unrestricted query
$all_comments = get_comments();

// Re-add the filter to maintain site privacy
add_filter('comments_clauses', ['WP_Private_Comments', 'filter_comments_by_privacy'], 10, 2);

SQL Query Modification