How WordPress attaches its Featured Images with posts?

You can upload images in 2 places:

Media page (uploads.php) or from Add Media button in a post/page edit page.

When you upload images from the post edit screen, 'post_parent' for all images uploaded is set to current post.

When you upload images from the Media page, 'post_parent' is set to 0.

When an image you have uploaded on media page is first inserted in the content of a post, or is included in a gallery inside the post, the 'post_parent' field is changed to the current post, just like it was uploaded using Add Media button of post edit screen.

As you noticed this does not happen for featured images, when an image uploaded on media page is used as featured image for a post, its post_parent stay unchanged.

Only thing that change is that a meta field '_thumbnail_id' is created for the post and its value is setted to the id of attachement post.

enter image description here

So if your post id is 10, get_post_meta(10, '_thumbnail_id', true); will return the ID of the post thumbnail.

Note that an image with post_parent setted to a post id does not mean that it’s inserted in the content of the post, it can be uploaded using the post Add Media button, but never inserted in the post content.

Also the countrary is true, an image inserted in the content of a post can have a post_parent setted to another post id.

Related Posts:

  1. Retrieve featured image (thumbnail) url from multiple posts with one query
  2. Query posts only with featured image
  3. Ignoring initial articles (like ‘a’, ‘an’ or ‘the’) when sorting queries?
  4. Should I use Transients with W3 Total Cache APC Caching? [closed]
  5. Add indexing to meta_value in wp_postmeta
  6. Get posts by menu ID
  7. Slow SQL_CALC_FOUND_ROWS Query
  8. In loop: posts have thumbnail AND other variables
  9. What is an efficient way to query based on post_meta?
  10. WP_Query Performance Issues with meta_query
  11. post thumb nail
  12. Trying to check and see if a post has a featured image outside of the main loop
  13. Should close $wpdb via $wpdb->close()
  14. Get the post permalink within the loop but without additional DB query
  15. Filter WordPress posts by between parameter
  16. Query sticky posts with thumbnails
  17. Get image of latest post from taxonomies/categories
  18. Multiple instances of Featured Image Query
  19. How To Get Some Data From WordPress Database Using WordPress $wpdb Query?
  20. post thumbnail not showing up with shortcode
  21. What’s faster? One big query, or several smaller ones?
  22. Order by custom table and multiplication
  23. why update and delete query not worked in custom table?
  24. getting post thumbnail within loop causes an error
  25. WP_Query condition affects posts_per_page count
  26. Site not getting correct featured image from my query
  27. How to implement a new row_count method in WordPress?
  28. querying data via $wpdb and get_row
  29. wp_Qwery works to slow
  30. Show all data in database table and make it into an interactive table
  31. Retrieve posts using thumbnail id as meta key
  32. No results found from a $wpdb->get_results() query when trying to join more than one meta key query
  33. WP Query – Post Thumbnail
  34. database query with more than a couple meta hangs and doesn’t complete
  35. How to access custom WordPress database tables
  36. How can I check for a thumbnail in WordPress?
  37. Is it possible to query from external database? [duplicate]
  38. how would i change post->ID to work correctly when querying pages?
  39. WP User Query with Custom Fields and Search Results
  40. How to display the featured image for each post?
  41. Query posts only without featured image
  42. List of ways to access WordPress database?
  43. Specify strict ‘order by’ in WordPress query
  44. How to set up hierarchical relationships without using plugins / meta query
  45. how to get Nearby zipcode
  46. Does WordPress have something like Drupal’s DB API?
  47. Using Transients
  48. Slow Query On Search
  49. how to write wordpress query for multiple metakeys checking?
  50. Wpdb->query result show 1 but is not an integer
  51. Why having more than 10 clauses in WP_Query results in some outputs being dropped?
  52. Storing an array of objects related to each user
  53. Retrieve data from wordpress db via input and put those result in dropdown
  54. WP Query – filtering terms with regex
  55. WP_Query with page_ids in arguments without a result
  56. Function to retrieve IDs of posts, cache results, and improve wp_query
  57. Issue with data array format
  58. the_post_thumbnail do 2 queries. How to optimize
  59. Featured images loop for Orbit Slider
  60. how to put thumbnail below category’s title?
  61. Why last row deleted when refresh page
  62. Query a database based on form input then output to another page [closed]
  63. wp query search multi terms
  64. How to get meta key list efficiently?
  65. How to get user avatar via WPDB
  66. How to extend WP_query to a specific table?
  67. Fix wp_term_relationships slow query in get_posts
  68. Translating WP query into to SQL query
  69. update_post_meta performance in a loop woocommerce
  70. update_post_meta performance in a loop woocommerce
  71. WP_Query how to add a thumbnail to the first post from the last 5 posts?
  72. WP_Term_Query->get_terms() very slow query for WordPress filter
  73. Separate by Category Post Type
  74. I removed the “wp_rm_logs” table and am constantly getting this error
  75. Track write actions to the database
  76. Featured Image as Background with Offset
  77. Trying to use “Medium” featured image for custom post type on home page
  78. wp_get_attachment_image not to get the post_thumbnaill
  79. Include post_status check within $wpdb query
  80. wpdb get_results() returns only 2 rows
  81. Website goes slow down after importing long database
  82. WP_Query always returning the last custom post
  83. option select form always deleting the sql query
  84. Optimising amount of calls to custom fields
  85. Featured image not showing on page
  86. Display First posts without the default featured image
  87. 294 Queries on Mainpage of WordPress
  88. how to add limit records in wordpress query
  89. Custom WP_query in Jnews theme returns thousands of posts
  90. WP_Query by meta key not returning any posts
  91. SQL query into to WP query
  92. Display only posts with thumbnails
  93. How to prevent writing duplicate loops?
  94. Meta box dropdown of custom posts
  95. Combining categories (Query posts with multiple taxonomy terms)
  96. wp_update_post not working
  97. How to create custom query by keyword in post title?
  98. How can I comment comma-separated array values?
  99. 3 wp_query on one page with pagination for last query
  100. Randomly display posts on a site hosted by WPEngine? [closed]
tech