Query parameters in Wordpress - Step-by-Step Execution

Concept Flow - Query parameters

User visits URL with query parameters

↓

WordPress reads URL

↓

Extract query parameters

↓

Modify WP_Query arguments

↓

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.

Practice

1. What is the main purpose of query parameters in WordPress when used with WP_Query?

easy

A. To create new user accounts automatically

B. To change the WordPress theme dynamically

C. To add custom CSS styles to posts

D. To filter and retrieve specific posts based on conditions like category or author

Solution

1. Step 1: Understand the role of query parameters

   Query parameters are used to specify conditions for retrieving posts, such as filtering by category or author.

2. Step 2: Identify the correct purpose in WordPress context

   They do not change themes, add styles, or create users; they filter content queries.

3. Final Answer:

   To filter and retrieve specific posts based on conditions like category or author -> Option D

4. Quick Check:

   Query parameters filter posts = D [OK]

Hint: Query parameters filter posts by conditions like category or author [OK]

Common Mistakes:

• Thinking query parameters change themes
• Confusing query parameters with styling or user management
• Assuming query parameters create new content

2. Which of the following is the correct way to query posts from category with ID 5 using WP_Query?

easy

A. $query = new WP_Query(array('category' => 5));

B. $query = new WP_Query(array('cat' => 5));

C. $query = new WP_Query(array('category_name' => 5));

D. $query = new WP_Query(array('category_id' => 5));

Solution

1. Step 1: Recall correct parameter for category ID

   The correct parameter to filter by category ID is 'cat', not 'category', 'category_name', or 'category_id'.

2. Step 2: Verify syntax correctness

   $query = new WP_Query(array('cat' => 5)); uses 'cat' with the ID 5 correctly in an array for WP_Query.

3. Final Answer:

   $query = new WP_Query(array('cat' => 5)); -> Option B

4. Quick Check:

   Category ID filter uses 'cat' = C [OK]

Hint: Use 'cat' key for category ID in WP_Query parameters [OK]

Common Mistakes:

• Using 'category' instead of 'cat' for category ID
• Passing category ID as 'category_name'
• Using 'category_id' which is invalid

3. What will be the result of this code snippet?

$args = array('author' => 3, 'posts_per_page' => 2);
$query = new WP_Query($args);
while ($query->have_posts()) {
  $query->the_post();
  echo get_the_title() . ', ';
}

medium

A. It will display the titles of the latest 2 posts by author with ID 3

B. It will display all posts by author with ID 3

C. It will cause a syntax error because 'author' is invalid

D. It will display 2 posts from any author

Solution

1. Step 1: Analyze query parameters

   'author' => 3 filters posts by author ID 3, 'posts_per_page' => 2 limits results to 2 posts.

2. Step 2: Understand loop output

   The loop outputs the titles of these posts separated by commas.

3. Final Answer:

   It will display the titles of the latest 2 posts by author with ID 3 -> Option A

4. Quick Check:

   Author filter + limit 2 posts = B [OK]

Hint: Author ID filters posts; posts_per_page limits number shown [OK]

Common Mistakes:

• Assuming 'author' is invalid parameter
• Thinking it shows all posts by author ignoring limit
• Believing it shows posts from any author

4. Identify the error in this query parameter usage:

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

medium

A. 'category' should be 'category_name' to filter by category slug

B. 'posts_per_page' must be a string, not a number

C. 'category' should be 'cat' with category slug

D. No error, this code works correctly

Solution

1. Step 1: Check parameter for category slug

   To filter by category slug (like 'news'), the correct parameter is 'category_name', not 'category'.

2. Step 2: Validate other parameters

   'posts_per_page' accepts a number, so that part is correct.

3. Final Answer:

   'category' should be 'category_name' to filter by category slug -> Option A

4. Quick Check:

   Category slug filter uses 'category_name' = A [OK]

Hint: Use 'category_name' for slug, 'cat' for ID in queries [OK]

Common Mistakes:

• Using 'category' instead of 'category_name' for slug
• Thinking 'posts_per_page' must be string
• Confusing 'cat' with slug instead of ID

5. You want to display posts that belong to category ID 4 or category ID 7 using WP_Query. Which query parameter array will correctly achieve this?

hard

A. array('category_name' => '4,7')

B. array('cat' => '4,7')

C. array('category__in' => array(4, 7))

D. array('cat' => array(4, 7))

Solution

1. Step 1: Understand how to query multiple categories

   To query posts in multiple categories by ID, use 'category__in' with an array of IDs.

2. Step 2: Evaluate each option

   array('cat' => '4,7') uses a string with comma which is invalid for 'cat'. array('category_name' => '4,7') uses 'category_name' with numbers which expects slugs. array('cat' => array(4, 7)) uses 'cat' with an array which is invalid.

3. Final Answer:

   array('category__in' => array(4, 7)) -> Option C

4. Quick Check:

   Multiple category IDs use 'category__in' with array = A [OK]

Hint: Use 'category__in' with array for multiple category IDs [OK]

Common Mistakes:

• Passing multiple IDs as comma string to 'cat'
• Using 'category_name' with numeric IDs
• Passing array to 'cat' which expects single ID