Why You Should Avoid Query_Posts() And Use Wp_Query In WordPress

Why query_posts() Should Be Avoided

The query_posts() function in WordPress has some significant drawbacks that can cause problems in your WordPress site. Here are some of the main issues with using query_posts():

The Problems With query_posts()

Alters the Main Query

One of the biggest issues with query_posts() is that it changes the main WordPress query that displays posts on archives, single posts, and pages. This can break pagination and have unintended consequences throughout the site. By altering the main query that controls the loop, functionality can be inadvertently broken.

Affects Pagination

By modifying the main loop query, the pagination ends up reflecting the altered query rather than the archives or page you are viewing. This breaks the pagination, where page numbers and posts per page counts will be impacted. It also presents the wrong posts for visitors clicking through numbered page links.

Hurts Performance

Every time query_posts() runs, it performs another database query then has to set up all the post data and related objects. This leads to slower load times. The impact multiplies if query_posts() appears in theme templates like archives or the homepage. Too many expensive queries hurt site speed.

Breaks Caching

Caching plugins store generated site pages to serve faster static page versions and avoid resource-intensive database queries. However, the results of query_posts() depend on the arguments passed. With unpredictable variables, the output changes too often for effective page caching.

Use WP_Query Instead

The WP_Query class gives developers and themers the power to perform customized database queries generating sets of WordPress posts without impacting the main query or site visitors. There are several benefits to embracing WP_Query over risky query_posts() calls.

Creating a Custom WP_Query

Basic WP_Query Syntax

At its simplest, WP_Query requires only a single line to instantiate a new object with the default results matching the main query:

$query = new WP_Query();

Passing an array with query parameters performs a fully customized database query returning posts matching criteria like post type, date, category, tags, custom fields, etc.

Query Arguments Overview

Dozens of options exist to perform selective queries that return specific posts. Key WP_Query arguments include:

• post_type – Custom post types or built-in types like post, page, etc.
• posts_per_page – Number of posts to return.
• order – ASC for oldest first, DESC for newest.
• orderby – Order by date, title, author, etc.
• category__in – Category IDs or slugs.
• tag__in – Tag IDs or slugs.

This only shows a sample of the possible parameter options when querying posts using WP_Query.

Benefits of WP_Query

Employing the flexibility of WP_Query over troublesome query_posts() calls comes with multiple advantages for WordPress developers. Keep these benefits in mind:

Safer and More Flexible

Because custom WP_Query instances do not impact the main query, website functionality and appearance remain unaffected. Developers enjoy greater flexibility and safer database queries through WP_Query.

Custom Queries Without Altering Main Query

Creating custom loops with targeted WP_Query parameters leaves the main WordPress query intact. This means pagination, archives, and all other areas relying on the main query work smoothly without conflicts.

Improved Performance

Performance stays optimized by only querying the database once per page load for what is needed on that specific page. Avoid slow secondary queries triggered by query_posts() everywhere.

Better for Caching

With consistent parameters in WP_Query instances, caching plugins can effectively store full page copies. Pages with query_posts() fail to cache properly since parameters often contain variables.

Example WP_Query Code

When leveraging WP_Query for custom post queries, use parameters appropriate to the desired results. Here are some common examples:

Query Posts by Category

$query = new WP_Query(array(
  'category_name' => 'news',
  'posts_per_page' => 5
));

Query Posts by Custom Field

 
$query = new WP_Query(array(
  'meta_key' => 'priority',
  'meta_value' => 'urgent'
));

Query Posts by Multiple Parameters

$query = new WP_Query(array(
  'tag__in' => array( 14, 183 ),
  'year' => 2022,
  'posts_per_page' => 10 
)); 

This displays the flexibility in querying the database for custom sets of posts using a wide variety of available parameters.

Conclusion

While query_posts() seems like an easy way to display custom post sets, it causes more harm than good in WordPress. Safer and more powerful options exist by embracing WP_Query.

Recap of Issues With query_posts()

In summary, problems caused by query_posts() include:

• Alters main query
• Breaks pagination
• Hurts performance with extra queries
• Fails to work with caching solutions

Summary of WP_Query Benefits

The WP_Query class solves all those issues and offers other advantages like:

• Safer, targeted database queries
• Custom post sets without impacting main query
• Improved performance
• Plays nice with page caching plugins

By avoiding risky query_posts() calls and building custom queries safely using WP_Query parameters, developers unlock greater power and flexibility in WordPress.