When clicking "Save" in Mercury Editor, if a Paragraph type has a field which references another Paragraph type, the .theme preprocess function is not able to access the the Target IDs contained within the field. This causes the Mercury editor preview to fail to render the Paragraph type content.
1.
Create a Paragraph type, "testing".
In this PT, create a field, ex: "field_paragraphs".
Have "field_paragraphs" reference another Paragraph Type:
2.
In your .theme file, create a paragraph preprocess function. Within this function, attempt to get the target IDs of the "field_paragraphs" field:
function my_theme_preprocess_paragraph(&$variables) {
$paragraph = $variables['paragraph'];
$paragraph_type = $paragraph->bundle();
$field_paragraphs = $paragraph->get('field_paragraphs')->getValue();
foreach ($field_paragraphs as $key=>$field_paragraph) {
$field_paragraph_data[$key] = $field_paragraph['target_id'];
}
$variables['field_paragraph_data'] = implode(" ", $field_paragraph_data);
Have your template reference the data, ex: {{ field_paragraph_data }}
3.
Using Mercury Editor, create a new "testing" paragraph type.
Fill its 'field_paragraphs' sub-fields with several values.
Upon saving, the Mercury Editor preview page will not display the values.
Closed: works as designed
2.1
Code
@jim_b Assuming by "Upon saving" you mean "Upon saving the 'testing' paragraph by clicking the save button in the dialog", the issue is that the nested paragraphs don't have a target ID yet. They won't acquire an ID until you save the entity by clicking save in the top right.
I'm going to close this, but please reopen if I am misunderstanding.