[9.x] Add firstOr methods to relationship classes

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

@@ -2,6 +2,7 @@
 
 namespace Illuminate\Database\Eloquent\Relations;
 
+use Closure;
 use Illuminate\Contracts\Support\Arrayable;
 use Illuminate\Database\Eloquent\Builder;
 use Illuminate\Database\Eloquent\Collection;
@@ -754,6 +755,28 @@ public function firstOrFail($columns = ['*'])
         throw (new ModelNotFoundException)->setModel(get_class($this->related));
     }
 
+    /**
+     * Execute the query and get the first result or call a callback.
+     *
+     * @param  \Closure|array  $columns
+     * @param  \Closure|null  $callback
+     * @return \Illuminate\Database\Eloquent\Model|static|mixed
+     */
+    public function firstOr($columns = ['*'], Closure $callback = null)
+    {
+        if ($columns instanceof Closure) {
+            $callback = $columns;
+
+            $columns = ['*'];
+        }
+
+        if (! is_null($model = $this->first($columns))) {
+            return $model;
+        }
+
+        return $callback();
+    }
+
     /**
      * Get the results of the relationship.
      *

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

@@ -2,6 +2,7 @@
 
 namespace Illuminate\Database\Eloquent\Relations;
 
+use Closure;
 use Illuminate\Contracts\Support\Arrayable;
 use Illuminate\Database\Eloquent\Builder;
 use Illuminate\Database\Eloquent\Collection;
@@ -301,6 +302,28 @@ public function firstOrFail($columns = ['*'])
         throw (new ModelNotFoundException)->setModel(get_class($this->related));
     }
 
+    /**
+     * Execute the query and get the first result or call a callback.
+     *
+     * @param  \Closure|array  $columns
+     * @param  \Closure|null  $callback
+     * @return \Illuminate\Database\Eloquent\Model|static|mixed
+     */
+    public function firstOr($columns = ['*'], Closure $callback = null)
+    {
+        if ($columns instanceof Closure) {
+            $callback = $columns;
+
+            $columns = ['*'];
+        }
+
+        if (! is_null($model = $this->first($columns))) {
+            return $model;
+        }
+
+        return $callback();
+    }
+
     /**
      * Find a related model by its primary key.
      *