[8.x] Warn if relation's foreign key is not in select list

src/Illuminate/Database/Eloquent/Relations/HasOneOrMany.php

@@ -6,6 +6,7 @@
 use Illuminate\Database\Eloquent\Collection;
 use Illuminate\Database\Eloquent\Model;
 use Illuminate\Database\Eloquent\Relations\Concerns\InteractsWithDictionary;
+use InvalidArgumentException;
 
 abstract class HasOneOrMany extends Relation
 {
@@ -175,13 +176,18 @@ protected function getRelationValue(array $dictionary, $key, $type)
      * Build model dictionary keyed by the relation's foreign key.
      *
      * @param  \Illuminate\Database\Eloquent\Collection  $results
+     * @throws \InvalidArgumentException
      * @return array
      */
     protected function buildDictionary(Collection $results)
     {
         $foreign = $this->getForeignKeyName();
 
         return $results->mapToDictionary(function ($result) use ($foreign) {
+            if (! isset($result->{$foreign})) {
+                throw new InvalidArgumentException('Relation needs foreign key "'.$result->qualifyColumn($foreign).'" to be fetched');
+            }
+
             return [$this->getDictionaryKey($result->{$foreign}) => $result];
         })->all();
     }

src/Illuminate/Database/Eloquent/Relations/Relation.php

@@ -12,6 +12,7 @@
 use Illuminate\Support\Arr;
 use Illuminate\Support\Traits\ForwardsCalls;
 use Illuminate\Support\Traits\Macroable;
+use InvalidArgumentException;
 
 /**
  * @mixin \Illuminate\Database\Eloquent\Builder
@@ -262,11 +263,16 @@ public function getRelationCountHash($incrementJoinCount = true)
      *
      * @param  array  $models
      * @param  string|null  $key
+     * @throws \InvalidArgumentException
      * @return array
      */
     protected function getKeys(array $models, $key = null)
     {
         return collect($models)->map(function ($value) use ($key) {
+            if (! isset($value->{$key})) {
+                throw new InvalidArgumentException('Relation needs parent key "'.$value->qualifyColumn($key).'" to be fetched');
+            }
+
             return $key ? $value->getAttribute($key) : $value->getKey();
         })->values()->unique(null, true)->sort()->all();
     }