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get_adjacent_post: Fix adjacent post navigation for posts with identical dates #10394

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get_adjacent_post: Fix adjacent post navigation for posts with identical dates #10394

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f8ffa69
Enhancement: Add ID-based fallback for adjacent post queries with ide…
ramonjd Oct 22, 2025
53ce5cc
Add periods to comments.
ramonjd Oct 22, 2025
790581b
Refactor: Prepare WHERE clause for adjacent post queries in `get_adja…
ramonjd Oct 22, 2025
9ce3cee
Update tests/phpunit/tests/url.php
ramonjd Oct 23, 2025
6f5a0ed
Update tests/phpunit/tests/url.php
ramonjd Oct 23, 2025
06ab623
Refactor: Rename variable for comparison operator in `get_adjacent_po…
ramonjd Oct 23, 2025
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13 changes: 9 additions & 4 deletions src/wp-includes/link-template.php
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Original file line number Diff line number Diff line change
Expand Up @@ -1939,8 +1939,8 @@ function get_adjacent_post( $in_same_term = false, $excluded_terms = '', $previo
$where .= " AND p.post_status = 'publish'";
}

$op = $previous ? '<' : '>';
$order = $previous ? 'DESC' : 'ASC';
$comparison_operator = $previous ? '<' : '>';
$order = $previous ? 'DESC' : 'ASC';

/**
* Filters the JOIN clause in the SQL for an adjacent post query.
Expand All @@ -1964,6 +1964,9 @@ function get_adjacent_post( $in_same_term = false, $excluded_terms = '', $previo
*/
$join = apply_filters( "get_{$adjacent}_post_join", $join, $in_same_term, $excluded_terms, $taxonomy, $post );

// Prepare the where clause for the adjacent post query.
$where_prepared = $wpdb->prepare( "WHERE (p.post_date $comparison_operator %s OR (p.post_date = %s AND p.ID $comparison_operator %d)) AND p.post_type = %s $where", $current_post_date, $current_post_date, $post->ID, $post->post_type ); // phpcs:ignore WordPress.DB.PreparedSQL.InterpolatedNotPrepared -- $comparison_operator is a string literal, either '<' or '>'.

/**
* Filters the WHERE clause in the SQL for an adjacent post query.
*
Expand All @@ -1977,14 +1980,15 @@ function get_adjacent_post( $in_same_term = false, $excluded_terms = '', $previo
*
* @since 2.5.0
* @since 4.4.0 Added the `$taxonomy` and `$post` parameters.
* @since 6.9.0 Adds ID-based fallback for posts with identical dates in adjacent post queries.
*
* @param string $where The `WHERE` clause in the SQL.
* @param bool $in_same_term Whether post should be in the same taxonomy term.
* @param int[]|string $excluded_terms Array of excluded term IDs. Empty string if none were provided.
* @param string $taxonomy Taxonomy. Used to identify the term used when `$in_same_term` is true.
* @param WP_Post $post WP_Post object.
*/
$where = apply_filters( "get_{$adjacent}_post_where", $wpdb->prepare( "WHERE p.post_date $op %s AND p.post_type = %s $where", $current_post_date, $post->post_type ), $in_same_term, $excluded_terms, $taxonomy, $post );
$where = apply_filters( "get_{$adjacent}_post_where", $where_prepared, $in_same_term, $excluded_terms, $taxonomy, $post );

/**
* Filters the ORDER BY clause in the SQL for an adjacent post query.
Expand All @@ -2000,12 +2004,13 @@ function get_adjacent_post( $in_same_term = false, $excluded_terms = '', $previo
* @since 2.5.0
* @since 4.4.0 Added the `$post` parameter.
* @since 4.9.0 Added the `$order` parameter.
* @since 6.9.0 Adds ID sort to ensure deterministic ordering for posts with identical dates.
*
* @param string $order_by The `ORDER BY` clause in the SQL.
* @param WP_Post $post WP_Post object.
* @param string $order Sort order. 'DESC' for previous post, 'ASC' for next.
*/
$sort = apply_filters( "get_{$adjacent}_post_sort", "ORDER BY p.post_date $order LIMIT 1", $post, $order );
$sort = apply_filters( "get_{$adjacent}_post_sort", "ORDER BY p.post_date $order, p.ID $order LIMIT 1", $post, $order );

$query = "SELECT p.ID FROM $wpdb->posts AS p $join $where $sort";
$key = md5( $query );
Expand Down
192 changes: 192 additions & 0 deletions tests/phpunit/tests/link/getAdjacentPost.php
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Expand Up @@ -587,4 +587,196 @@ public function test_get_adjacent_post_cache() {
$this->assertEquals( $post_four, get_adjacent_post( true, '', false ), 'Result of function call is wrong after after adding new term' );
$this->assertSame( get_num_queries() - $num_queries, 2, 'Number of queries run was not two after adding new term' );
}

/**
* Test get_adjacent_post with posts having identical post_date.
*
* @ticket 8107
*/
public function test_get_adjacent_post_with_identical_dates() {
$identical_date = '2024-01-01 12:00:00';

// Create posts with identical dates but different IDs.
$post_ids = array();
for ( $i = 1; $i <= 5; $i++ ) {
$post_ids[] = self::factory()->post->create(
array(
'post_title' => "Post $i",
'post_date' => $identical_date,
)
);
}

// Test navigation from the middle post (ID: 3rd post).
$current_post_id = $post_ids[2]; // 3rd post
$this->go_to( get_permalink( $current_post_id ) );

// Previous post should be the 2nd post (lower ID, same date).
$previous = get_adjacent_post( false, '', true );
$this->assertInstanceOf( 'WP_Post', $previous );
$this->assertEquals( $post_ids[1], $previous->ID );

// Next post should be the 4th post (higher ID, same date).
$next = get_adjacent_post( false, '', false );
$this->assertInstanceOf( 'WP_Post', $next );
$this->assertEquals( $post_ids[3], $next->ID );
}

/**
* Test get_adjacent_post with mixed dates and identical dates.
*
* @ticket 8107
*/
public function test_get_adjacent_post_mixed_dates_with_identical_groups() {
// Create posts with different dates.
$post_early = self::factory()->post->create(
array(
'post_title' => 'Early Post',
'post_date' => '2024-01-01 10:00:00',
)
);

// Create multiple posts with identical date.
$identical_date = '2024-01-01 12:00:00';
$post_ids = array();
for ( $i = 1; $i <= 3; $i++ ) {
$post_ids[] = self::factory()->post->create(
array(
'post_title' => "Identical Post $i",
'post_date' => $identical_date,
)
);
}

$post_late = self::factory()->post->create(
array(
'post_title' => 'Late Post',
'post_date' => '2024-01-01 14:00:00',
)
);

// Test from first identical post.
$this->go_to( get_permalink( $post_ids[0] ) );

// Previous should be the early post (different date).
$previous = get_adjacent_post( false, '', true );
$this->assertInstanceOf( 'WP_Post', $previous );
$this->assertEquals( $post_early, $previous->ID );

// Next should be the second identical post (same date, higher ID).
$next = get_adjacent_post( false, '', false );
$this->assertInstanceOf( 'WP_Post', $next );
$this->assertEquals( $post_ids[1], $next->ID );

// Test from middle identical post.
$this->go_to( get_permalink( $post_ids[1] ) );

// Previous should be the first identical post (same date, lower ID).
$previous = get_adjacent_post( false, '', true );
$this->assertInstanceOf( 'WP_Post', $previous );
$this->assertEquals( $post_ids[0], $previous->ID );

// Next should be the third identical post (same date, higher ID).
$next = get_adjacent_post( false, '', false );
$this->assertInstanceOf( 'WP_Post', $next );
$this->assertEquals( $post_ids[2], $next->ID );

// Test from last identical post.
$this->go_to( get_permalink( $post_ids[2] ) );

// Previous should be the second identical post (same date, lower ID).
$previous = get_adjacent_post( false, '', true );
$this->assertInstanceOf( 'WP_Post', $previous );
$this->assertEquals( $post_ids[1], $previous->ID );

// Next should be the late post (different date).
$next = get_adjacent_post( false, '', false );
$this->assertInstanceOf( 'WP_Post', $next );
$this->assertEquals( $post_late, $next->ID );
}

/**
* Test get_adjacent_post navigation through all posts with identical dates.
*
* @ticket 8107
*/
public function test_get_adjacent_post_navigation_through_identical_dates() {
$identical_date = '2024-01-01 12:00:00';

// Create 4 posts with identical dates.
$post_ids = array();
for ( $i = 1; $i <= 4; $i++ ) {
$post_ids[] = self::factory()->post->create(
array(
'post_title' => "Post $i",
'post_date' => $identical_date,
)
);
}

// Test navigation sequence: 1 -> 2 -> 3 -> 4.
$this->go_to( get_permalink( $post_ids[0] ) );

// From post 1, next should be post 2.
$next = get_adjacent_post( false, '', false );
$this->assertEquals( $post_ids[1], $next->ID );

// From post 2, previous should be post 1, next should be post 3.
$this->go_to( get_permalink( $post_ids[1] ) );
$previous = get_adjacent_post( false, '', true );
$this->assertEquals( $post_ids[0], $previous->ID );
$next = get_adjacent_post( false, '', false );
$this->assertEquals( $post_ids[2], $next->ID );

// From post 3, previous should be post 2, next should be post 4.
$this->go_to( get_permalink( $post_ids[2] ) );
$previous = get_adjacent_post( false, '', true );
$this->assertEquals( $post_ids[1], $previous->ID );
$next = get_adjacent_post( false, '', false );
$this->assertEquals( $post_ids[3], $next->ID );

// From post 4, previous should be post 3.
$this->go_to( get_permalink( $post_ids[3] ) );
$previous = get_adjacent_post( false, '', true );
$this->assertEquals( $post_ids[2], $previous->ID );
}

/**
* Test get_adjacent_post with identical dates and category filtering.
*
* @ticket 8107
*/
public function test_get_adjacent_post_identical_dates_with_category() {
$identical_date = '2024-01-01 12:00:00';
$category_id = self::factory()->category->create( array( 'name' => 'Test Category' ) );

// Create posts with identical dates, some in category.
$post_ids = array();
for ( $i = 1; $i <= 4; $i++ ) {
$post_id = self::factory()->post->create(
array(
'post_title' => "Post $i",
'post_date' => $identical_date,
)
);

// Add every other post to the category.
if ( 0 === $i % 2 ) {
wp_set_post_categories( $post_id, array( $category_id ) );
}

$post_ids[] = $post_id;
}

// Test from post 2 (in category).
$this->go_to( get_permalink( $post_ids[1] ) );

// With category filtering, should only see posts in same category.
$previous = get_adjacent_post( true, '', true, 'category' );
$this->assertSame( '', $previous ); // No previous post in category

$next = get_adjacent_post( true, '', false, 'category' );
$this->assertInstanceOf( 'WP_Post', $next );
$this->assertEquals( $post_ids[3], $next->ID ); // Post 4 (in category)
}
}
58 changes: 58 additions & 0 deletions tests/phpunit/tests/url.php
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Original file line number Diff line number Diff line change
Expand Up @@ -569,4 +569,62 @@ public function test_url_functions_for_dots_in_paths() {
);
}
}

/**
* Test get_adjacent_post with posts having identical post_date.
*
* @ticket 8107
* @covers ::get_adjacent_post
*/
public function test_get_adjacent_post_with_identical_dates() {
$identical_date = gmdate( 'Y-m-d H:i:s', time() );

// Create 3 posts with identical dates but different IDs.
$post_ids = array();
for ( $i = 1; $i <= 3; $i++ ) {
$post_ids[] = self::factory()->post->create(
array(
'post_title' => "Identical Post $i",
'post_date' => $identical_date,
)
);
}

// Test from the middle post (2nd post).
$GLOBALS['post'] = get_post( $post_ids[1] );

// Previous post should be the 1st post (lower ID, same date).
$previous = get_adjacent_post( false, '', true );
$this->assertInstanceOf( 'WP_Post', $previous );
$this->assertSame( $post_ids[0], $previous->ID );

// Next post should be the 3rd post (higher ID, same date).
$next = get_adjacent_post( false, '', false );
$this->assertInstanceOf( 'WP_Post', $next );
$this->assertSame( $post_ids[2], $next->ID );

// Test from the first post.
$GLOBALS['post'] = get_post( $post_ids[0] );

// Previous should be empty (no earlier posts).
$previous = get_adjacent_post( false, '', true );
$this->assertSame( '', $previous );

// Next should be the 2nd post.
$next = get_adjacent_post( false, '', false );
$this->assertInstanceOf( 'WP_Post', $next );
$this->assertSame( $post_ids[1], $next->ID );

// Test from the last post.
$GLOBALS['post'] = get_post( $post_ids[2] );

// Previous should be the 2nd post.
$previous = get_adjacent_post( false, '', true );
$this->assertInstanceOf( 'WP_Post', $previous );
$this->assertSame( $post_ids[1], $previous->ID );

// Next should be empty (no later posts).
$next = get_adjacent_post( false, '', false );
$this->assertSame( '', $next );
}
}
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