Feed entity validation misses form validation logic

taking

+++ b/core/modules/aggregator/src/Plugin/Validation/Constraint/FeedConstraintValidatorBase.php
@@ -0,0 +1,70 @@
+  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
+    return new static($container->get('entity_manager')->getStorage('aggregator_feed'));
+  }
+
+  /**
+   * Returns the feed storage handler.
+   *
+   * @return \Drupal\aggregator\FeedStorageInterface|\Drupal\Core\Entity\EntityStorageInterface
+   *   The feed storage handler.
+   */
+  protected function feedStorage() {
+    if (!$this->feedStorage) {
+      $this->feedStorage = \Drupal::entityManager()->getStorage('aggregator_feed');
+    }
+    return $this->feedStorage;
+  }

Why do we need both?

Any chance we can find a way to write a generic unique field constraint? I know that for example BlockContent needs that too.

And there's nothing in FeedStorage::getFeedDuplicates() that is feed specific, it's just an entity query?

Why do we need both?

Cause it no-worky. See #2197029: Allow to inject dependencies into validation constraints

Any chance we can find a way to write a generic unique field constraint?

Sure but should we do that as a non-critical follow up?

And there's nothing in FeedStorage::getFeedDuplicates() that is feed specific, it's just an entity query?

yes. relevant: #2228733: Remove getFeedDuplicates - its unused and untested

Should we postpone this on #2197029: Allow to inject dependencies into validation constraints to address comment #4?

Should be able to guide any newcomers through this in today's office hours

Fixes #4 #5 and #10 I think this is pretty close

Great extraction of existing logic.

Now we have worked on moving code around, but nothing actually ensures that the critical is fixed: Validation is executed on an API / REST level,
the test still just deals with forms.

+++ b/core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/UniqueFieldValueValidator.php
@@ -0,0 +1,43 @@
+    $value_taken = (bool) \Drupal::entityQuery($entity_type_id)

We still can't inject things? Too bad.

added a test

rtbc'd the injections issue

getting close now

Cool, thank you!

This issue addresses a critical bug and is allowed per https://www.drupal.org/core/beta-changes. Committed 2a55451 and pushed to 8.0.x. Thanks!

Filed a follow-up here #2483869: Make Unique Field constraints generic