EntityInterface::uriRelationships() should document you can't call it on a new entity

Here is the documentation added. Please review. Thanks:)

Thanks for helping to improve our documentation!

+++ b/core/lib/Drupal/Core/Entity/EntityInterface.php
@@ -230,6 +230,9 @@ public function hasLinkTemplate($key);
+   * The entity must have an id already. Content entities usually get their IDs

s/id/ID/

("IDs" later in the sentence gets it right.)

If we're going to document this behaviour couldn't we do it with an @throws?

However thinking about this conceptually should we catch the exception in \Drupal\Core\Entity\Entity::uriRelationships i.e do something like:

      // It's not guaranteed that every link relation type also has a
      // corresponding route. For some, additional modules or configuration may
      // be necessary. The interface demands that we only return supported URI
      // relationships.
      try {
        $this->toUrl($link_relation_type)->toString(TRUE)->getGeneratedUrl();
      }
      catch (RouteNotFoundException $e) {
        return FALSE;
      }
      catch (EntityMalformedException $e) {
        return FALSE;
      }

The text at the top is interesting as it says

The interface demands that we only return supported URI relationships.

and what we're saying is that until the entity has an ID it doesn't support any URI relationships so this returns an empty array - rather than throwing an exception.

Tagging for subsystem maintainer review.

#2924338: Entity::uriRelationships() throws exceptions if an URL cannot be generated because of missing mandatory parameters is a similar issue and even has a patch.

@alexpott, shouldn't the thrown exception here be of type MissingMandatoryParametersException like in the other issue?

However thinking about this conceptually should we catch the exception in \Drupal\Core\Entity\Entity::uriRelationships

Yes, I think we should catch the exceptions that are thrown if we could not generate a URL because of missing parameters. I think the solution for both issues has to be the same, as \Drupal\Core\Entity\Entity::uriRelationships() should not throw exceptions, but instead filter out the URI relationships that couldn't be automatically generated.

If you are fine with this I would close the current issue as a duplicate and move the discussion to the referenced one.

@hchonov yep I agree this is a duplicate of that.

I don't know if this is the right place for this, but the patch commited in #2924338 only catches MissingMandatoryParametersException , but there is also the case where an EntityMalformedException is thrown, so I am reopening this so we can fix it. In the spirit of #2924338, I am attaching a patch that catches that as well.

Looks ok..

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