Adding fields to attachment - only shows when inserting new attachments

Question

I'd like to add two custom text fields for image attachments to posts (images inserted into the content of a post). Second I'd also like to remote some of the default fields like caption and description.

I've managed to add fields like so:

add_filter('attachment_fields_to_edit', array($this, 'applyFilter'), 1, 2);

public function applyFilter( $form_fields, $post = null ) {

    $form_fields['someCustom'] = array(
        'label' => 'Image credit',
        'input'       => 'text',
        'helps'       => 'Photographer / bureau',
        'application' => 'image',
        'exclusions'  => array( 'audio', 'video' ),
        'required'    => true,
        'error_text'  => 'Credit field required',
    );
    return $form_fields;
}

This adds the field within the media library modal, but only when inserting new images - not when editing existing images. Also the required parameter doesn't seem to prevent inserting images even when the field is empty.

No matter how I set the priority of the filter (tried everything from null, to 1, to 100) it seems to run before the default fields are added to form_fields, making it impossible to remove any default fields.

I'd very much appreciate any help in the matter.

Answer 1

Okay I think I have it, you need to add a matching filter to attachment_fields_to_save to save the new field (say as post meta to the attachment.)

add_filter( 'attachment_fields_to_save', 'save_some_custom_field', 10, 2 );
function save_some_custom_field($post, $attachment) {
    $attachid = $post['ID']; // yes this is actually an array here
    update_post_meta($attachid,'someCustom',$attachment['someCustom']);
}

Then you would add to your $form_fields edit filter array something like:

'value' => get_post_meta($post->ID,'someCustom',true),

...remembering to remove the = null from the function arguments.

unset($form_fields['post_excerpt']); and unset($form_fields['post_content']); in the edit filter should remove caption and description fields respectively, not sure on the required part though.