Afform - Do not set LocBlock id if exposed to the form

ext/afform/core/Civi/Api4/Action/Afform/Submit.php

@@ -460,8 +460,8 @@ class Submit extends AbstractProcessor {
       // Forward FK e.g. Event.loc_block_id => LocBlock
       $forwardFkField = self::getFkField($mainEntity['type'], $joinEntityName);
       if ($forwardFkField && $values) {
-        // Add id to values for update op
-        if ($whereClause) {
+        // Add id to values for update op, but only if id is not already on the form
+        if ($whereClause && empty($mainEntity['joins'][$joinEntityName]['fields'][$joinIdField])) {
           $values[0][$joinIdField] = $whereClause[0][2];
         }
         $result = civicrm_api4($joinEntityName, 'save', [

ext/afform/mock/tests/phpunit/api/v4/Afform/AfformEventUsageTest.php

@@ -2,13 +2,14 @@
 namespace api\v4\Afform;
 
 use Civi\Api4\Afform;
+use Civi\Test\TransactionalInterface;
 
 /**
  * Test case for Afform.prefill and Afform.submit with Event records.
  *
  * @group headless
  */
-class AfformEventUsageTest extends AfformUsageTestCase {
+class AfformEventUsageTest extends AfformUsageTestCase implements TransactionalInterface {
   use \Civi\Test\Api4TestTrait;
 
   /**
@@ -75,4 +76,110 @@ EOHTML;
     $this->assertSame('2234567', $prefill['values'][0]['joins']['LocBlock'][0]['phone_id.phone']);
   }
 
+  /**
+   * Test saving & updating
+   */
+  public function testEventLocationUpdate(): void {
+    $layout = <<<EOHTML
+<af-form ctrl="afform">
+  <af-entity actions="{create: true, update: true}" type="Event" name="Event1" label="Event 1" security="FBAC" />
+  <fieldset af-fieldset="Event1" class="af-container" af-title="Event 1">
+    <af-field name="id" />
+    <af-field name="title" />
+    <af-field name="start_date" />
+    <af-field name="event_type_id" />
+    <div af-join="LocBlock">
+      <af-field name="id" />
+      <af-field name="email_id.email" />
+      <af-field name="address_id.street_address" />
+    </div>
+  </fieldset>
+  <button class="af-button btn btn-primary" crm-icon="fa-check" ng-click="afform.submit()">Submit</button>
+</af-form>
+EOHTML;
+
+    $this->useValues([
+      'layout' => $layout,
+      'permission' => \CRM_Core_Permission::ALWAYS_ALLOW_PERMISSION,
+    ]);
+
+    // Create a new event with a new location
+    $submit = Afform::submit()
+      ->setName($this->formName)
+      ->setValues([
+        'Event1' => [
+          [
+            'fields' => [
+              'title' => 'Event Title 1',
+              'start_date' => '2021-01-01 00:00:00',
+              'event_type_id' => 1,
+            ],
+            'joins' => [
+              'LocBlock' => [
+                [
+                  'email_id.email' => 'test1@te.st',
+                  'address_id.street_address' => '12345',
+                ],
+              ],
+            ],
+          ],
+        ],
+      ])->execute();
+
+    $event1 = $submit[0]['Event1'][0]['id'];
+    $loc1 = $submit[0]['Event1'][0]['joins']['LocBlock'][0]['id'];
+
+    // Create a 2nd new event with a new location
+    $submit = Afform::submit()
+      ->setName($this->formName)
+      ->setValues([
+        'Event1' => [
+          [
+            'fields' => [
+              'title' => 'Event Title 2',
+              'start_date' => '2022-01-01 00:00:00',
+              'event_type_id' => 1,
+            ],
+            'joins' => [
+              'LocBlock' => [
+                [
+                  'id' => $loc1,
+                ],
+              ],
+            ],
+          ],
+        ],
+      ])->execute();
+
+    $event2 = $submit[0]['Event1'][0]['id'];
+    $this->assertGreaterThan($event1, $event2);
+    $this->assertSame($loc1, $submit[0]['Event1'][0]['joins']['LocBlock'][0]['id']);
+
+    // Update event 1 with a new location
+    $submit = Afform::submit()
+      ->setName($this->formName)
+      ->setValues([
+        'Event1' => [
+          [
+            'fields' => [
+              'id' => $event1,
+              'title' => 'Event Title 1 Updated',
+            ],
+            'joins' => [
+              'LocBlock' => [
+                [
+                  'id' => NULL,
+                  'address_id.street_address' => '12345',
+                ],
+              ],
+            ],
+          ],
+        ],
+      ])->execute();
+
+    $this->assertSame($event1, $submit[0]['Event1'][0]['id']);
+    $this->assertGreaterThan($loc1, $submit[0]['Event1'][0]['joins']['LocBlock'][0]['id']);
+
+  }
+
 }