Fix #1959 do not join same association twice

Author: abluchet

features/main/circular_reference.feature

@@ -61,10 +61,29 @@ Feature: Circular references handling
           "@type": "CircularReference",
           "parent": "/circular_references/1",
           "children": [
-              "/circular_references/1",
-              "/circular_references/2"
+              "/circular_references/1"
           ]
       },
       "children": []
     }
     """
+    And I send a "GET" request to "/circular_references/1"
+    Then the response status code should be 200
+    And the JSON should be equal to:
+    """
+    {
+        "@context": "/contexts/CircularReference",
+        "@id": "/circular_references/1",
+        "@type": "CircularReference",
+        "parent": "/circular_references/1",
+        "children": [
+            "/circular_references/1",
+            {
+                "@id": "/circular_references/2",
+                "@type": "CircularReference",
+                "parent": "/circular_references/1",
+                "children": []
+            }
+        ]
+    }
+    """

src/Bridge/Doctrine/Orm/Extension/EagerLoadingExtension.php

@@ -200,9 +200,13 @@ private function joinRelations(QueryBuilder $queryBuilder, QueryNameGeneratorInt
                 $queryBuilder->addSelect($associationAlias);
             }
 
-            // Avoid recursion
+            // Avoid recursive joins
             if ($mapping['targetEntity'] === $resourceClass) {
-                $queryBuilder->addSelect($associationAlias);
+                // Avoid joining the same association twice (see #1959)
+                if (!\in_array($associationAlias, $queryBuilder->getAllAliases(), true)) {
+                    $queryBuilder->addSelect($associationAlias);
+                }
+
                 continue;
             }