Query parameters in Wordpress - Step-by-Step Execution

Concept Flow - Query parameters

User visits URL with query parameters

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WordPress reads URL

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Extract query parameters

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Modify WP_Query arguments

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Run WP_Query with parameters

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Display filtered posts or content

WordPress reads the URL query parameters, uses them to adjust the WP_Query arguments, then fetches and shows the filtered content.

Execution Sample

Wordpress

<?php
$args = array('category_name' => $_GET['cat'] ?? '', 'posts_per_page' => 5);
$query = new WP_Query($args);
while ($query->have_posts()) {
  $query->the_post();
  the_title();
}
wp_reset_postdata();

This code reads the 'cat' query parameter from the URL and shows 5 posts from that category.

Execution Table

Step	Action	Query Parameter 'cat'	WP_Query Args	Posts Fetched
1	User visits URL with ?cat=technology	technology	category_name='technology', posts_per_page=5	Not fetched yet
2	PHP reads $_GET['cat']	technology	category_name='technology', posts_per_page=5	Not fetched yet
3	Create WP_Query with args	technology	category_name='technology', posts_per_page=5	Query prepared
4	Run have_posts() loop	technology	category_name='technology', posts_per_page=5	Posts from 'technology' category fetched
5	Display post titles	technology	category_name='technology', posts_per_page=5	Titles shown on page
6	Reset post data	technology	category_name='technology', posts_per_page=5	Post data reset
7	End of script	technology	category_name='technology', posts_per_page=5	Execution complete

💡 All posts matching category 'technology' displayed, loop ends when no more posts.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
$_GET['cat']	undefined	technology	technology	technology	technology
$args	empty array	array('category_name' => 'technology', 'posts_per_page' => 5)	same	same	same
$query	undefined	undefined	WP_Query object created	WP_Query object with posts	WP_Query object reset

Key Moments - 2 Insights

Why does $_GET['cat'] sometimes cause an error if the URL has no 'cat' parameter?

Because $_GET['cat'] is undefined if the parameter is missing. Using the null coalescing operator (?? '') avoids this by providing a default empty string, as shown in execution_table step 2.

Why do we call wp_reset_postdata() after the loop?

Because WP_Query changes global post data during the loop. Resetting it restores the original state, preventing side effects on other parts of the page, as seen in execution_table step 6.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of $args after step 3?

A empty array

B array('category_name' => 'technology', 'posts_per_page' => 5)

C undefined

D array('category_name' => '', 'posts_per_page' => 5)

💡 Hint

Check the 'WP_Query Args' column at step 3 in the execution_table.

At which step does WordPress fetch posts from the database?

A Step 6

B Step 2

C Step 4

D Step 1

💡 Hint

Look at the 'Posts Fetched' column in the execution_table.

If the URL has no 'cat' parameter, what would $args['category_name'] be?

A empty string ''

B null

C undefined

D the string 'cat'

💡 Hint

Refer to the code sample where $_GET['cat'] uses ?? '' to provide a default.

Concept Snapshot

Query parameters in WordPress are read from the URL using $_GET.
Use these parameters to build WP_Query arguments.
Run WP_Query to fetch posts matching those parameters.
Always handle missing parameters safely with ?? operator.
Reset post data after custom queries with wp_reset_postdata().

Full Transcript

When a user visits a WordPress site with query parameters in the URL, WordPress reads these parameters using PHP's $_GET array. For example, if the URL has ?cat=technology, the code reads $_GET['cat'] to get 'technology'. This value is used to build arguments for WP_Query, such as setting 'category_name' to 'technology' and limiting posts to 5. WP_Query then fetches posts matching these arguments. The loop runs to display the post titles. After the loop, wp_reset_postdata() is called to restore the original global post data. This process allows WordPress to dynamically filter and display content based on URL query parameters.