functions - Automatically set the featured image

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How would I change every post so that they had the same, hard-coded featured image?! Say this cigar:

.jpeg

(I don't actually want to do this - but it's a stumbling block in something more complex.)

I think it ought to be this:

function set_post_thumbnail( $post, $thumbnail_id ) {
    $thumbnail_id = ".jpeg";
    update_post_meta( $post->ID, '_thumbnail_id', $thumbnail_id );

}

add_action( 'save_post', 'set_post_thumbnail' );

... but no cigar. What am I missing? Thanks!

How would I change every post so that they had the same, hard-coded featured image?! Say this cigar:

https://www.cigarsofcuba.co.uk/acatalog/slide1.jpeg

(I don't actually want to do this - but it's a stumbling block in something more complex.)

I think it ought to be this:

function set_post_thumbnail( $post, $thumbnail_id ) {
    $thumbnail_id = "https://www.cigarsofcuba.co.uk/acatalog/slide1.jpeg";
    update_post_meta( $post->ID, '_thumbnail_id', $thumbnail_id );

}

add_action( 'save_post', 'set_post_thumbnail' );

... but no cigar. What am I missing? Thanks!

• functions
• post-thumbnails

Share Improve this question asked Feb 26, 2018 at 18:39 JohnGJohnG 34433 silver badges1717 bronze badges 2

• Thumbnail id is supposed to be an ID, not a URL - it has to be something that's already in the Media Library. Upload the file to the library, then when you view the attachment details you can see its ID. Set that number as $thumbnail_id. – WebElaine Commented Feb 26, 2018 at 19:13
• Thanks Elaine - useful info to know for the future... It's not solving my current problem though. – JohnG Commented Feb 27, 2018 at 9:36

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3 Answers 3

Sorted by: Reset to default 4

Method 1: Using the publish_post hook* and media_sideload_image()

Here we will upload an image from a URL, attach it to the post, and set it as the featured image when the post is published.

*Actually, we're using the dynamic hook {$new_status}_{$post->post_type}, which refers transitioning a post post type to the publish status. See wp-includes/post.php for details.

This example code applies when publishing the post type post. A check is in place so that we do not automatically assign the featured image if one has been manually set. Feel free to customize this as desired.

/**
 * Download image, attach it to the current post, and assign it as featured image
 * upon publishing the post.
 *
 * The dynamic portions of the hook name, `$new_status` and `$post->post_type`,
 * refer to the new post status and post type, respectively.
 *
 * Please note: When this action is hooked using a particular post status (like
 * 'publish', as `publish_{$post->post_type}`), it will fire both when a post is
 * first transitioned to that status from something else, as well as upon
 * subsequent post updates (old and new status are both the same).
 *
 * @param int     $post_id Post ID.
 * @param WP_Post $post    Post object.
 */
add_action( 'publish_post', 'wpse_default_featured_image', 10, 2 );
function wpse_default_featured_image( $post_id, $post ) {
    // Bail if there is already a post thumbnail set.
    $current_post_thumbnail = get_post_thumbnail_id( $post_id );
    if ( '' !== $current_post_thumbnail ) {
        return;
    }

    $url = 'https://www.cigarsofcuba.co.uk/acatalog/slide1.jpeg';
    $title = "The default featured image.";

    $image = media_sideload_image( $url, $post_id, $title, 'id' );
    set_post_thumbnail( $post_id, $image );
}

Method 2: Applying a filter to the post thumbnail.

By using a filter, we can "virtually" set the post thumbnail. This method makes it easier to change the post thumbnail on the fly for all posts.

Filter 1: post_thumbnail_html

The post_thumbnail_html filter can be used to override the HTML output for the post thumbnail:

/**
 * Filters the post thumbnail HTML.
 *
 * @param string       $html              The post thumbnail HTML.
 * @param int          $post_id           The post ID.
 * @param string       $post_thumbnail_id The post thumbnail ID.
 * @param string|array $size              The post thumbnail size. Image size or array of width and height
 *                                        values (in that order). Default 'post-thumbnail'.
 * @param string       $attr              Query string of attributes.
 */
add_filter( 'post_thumbnail_html', 'wpse_post_thumbnail_html', 10, 5 );
function wpse_post_thumbnail_html( $html, $post_id, $post_thumbnail_id, $size, $attr ) {
    return '<img src="https://www.cigarsofcuba.co.uk/acatalog/slide1.jpeg" alt="Have a cigar">';
}

Filter 2: Using get_post_metadata on the _thumbnail_id meta key.

Here's another approach that overrides each post's thumbnail ID with a different ID.

I'd suggest implementing a Customizer setting or options page that allows the special thumbnail image to be uploaded/selected (locally, from a URL, or from the medial library). Then you can use the get_post_metadata filter to modify the value associated with each post thumbnail's meta key _thumbnail_id:

/**
 * Dynamic hook: "get_{$meta_type}_metadata"
 * 
 * Filters whether to retrieve metadata of a specific type.
 * 
 * The dynamic portion of the hook, `$meta_type`, refers to the meta
 * object type (comment, post, or user). Returning a non-null value
 * will effectively short-circuit the function.
 *
 * @param null|array|string $value     The value get_metadata() should return - a single metadata value,
 *                                     or an array of values.
 * @param int               $object_id Object ID.
 * @param string            $meta_key  Meta key.
 * @param bool              $single    Whether to return only the first value of the specified $meta_key.
 */
add_filter( 'get_post_metadata', 'wpse_featured_image_id_override', 100, 4 );
function wpse_featured_image_id_override( $value, $object_id, $meta_key, $single ) {
    $thumbnail_id_key = '_thumbnail_id';

    // Bail if this is not the correct meta key. Return the original value  immediately.
    if ( ! isset( $meta_key ) || $thumbnail_id_key !== $meta_key ) {
        return $value;
    }

    // Add additional guard clauses if necessary... (check post type, etc.)

    // Get the id for an image uploaded elsewhere.
    // This could be pulled from the customizer or a plugin options page.
    return 807;  // Example ID
}

You could simply overwrite the featured image (whether one is set or not) on saving the page / post with this:

//this is called on saving page/post
add_action('save_post', 'force_featured_image');

function force_featured_image( $post_id ){
   //set the featured image
   set_post_thumbnail( $post_id, [image_id] );
}

NOTE Replace '[image_id]' with your image id.

function wpb_autolink_featured_images( $html, $post_id, $post_image_id ) {
    if (! is_singular()) {
        $html = '<a href="' . get_permalink( $post_id ) . '" title="' 
                . esc_attr( get_the_title( $post_id ) ) . '">' . $html . '</a>';
        return $html;
    } else {
        return $html;
    }
}
add_filter( 'post_thumbnail_html', 'wpb_autolink_featured_images', 10, 3 );

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