Create basic field data in template like node for custom entities {{ custom_entity.id }}

Question

I see node preprocess does this

$variables['node'] = $variables['elements']['#node'];

and then in the template one can do this

{{ node.id }}

but when I create a custom entity and do the same, I never get past all the the errors like

Exception: Object of type Drupal\Core\Field\FieldItemList cannot be printed. in Drupal\Core\Template\TwigExtension->escapeFilter() (line 476 of core/lib/Drupal/Core/Template/TwigExtension.php).

What are they doing special for node?

Answer 1

Why does {{ custom_entity.id }} produce this error message?

Exception: Object of type Drupal\Core\Field\FieldItemList cannot be printed.

If your entity defines id for the entity ID then {{ custom_entity.id }} is ambiguous. It can mean the object property (the ID field) or the method EntityInterface::id().

So use parentheses to make it clear it is a method:

{{ custom_entity.id() }}

Or retrieve the field value when you have already a field as the error message shows:

{{ custom_entity.id.value }}

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What are they doing special for node?

The node entity is using nid as ID field, so id and nid are unambigious.

Method id():

{{ node.id }}

Field nid:

{{ node.nid.value }}