Throw exception if using unsupported callback

src/Exceptions/SingleCallbackNotAllowed.php

@@ -0,0 +1,11 @@
+<?php
+
+namespace Kirschbaum\PowerJoins\Exceptions;
+
+use Exception;
+
+class SingleCallbackNotAllowed extends Exception
+{
+    /** The error message */
+    protected $message = 'Single callback is not allowed here.';
+}

src/Mixins/RelationshipsExtraMethods.php

@@ -16,6 +16,7 @@
 use Illuminate\Database\Eloquent\SoftDeletingScope;
 use Illuminate\Database\MySqlConnection;
 use Illuminate\Support\Str;
+use Kirschbaum\PowerJoins\Exceptions\SingleCallbackNotAllowed;
 use Kirschbaum\PowerJoins\PowerJoinClause;
 use Kirschbaum\PowerJoins\StaticCache;
 
@@ -129,6 +130,8 @@ protected function performJoinForEloquentPowerJoinsForBelongsToMany()
 
                 if (is_array($callback) && isset($callback[$this->getTable()])) {
                     $callback[$this->getTable()]($join);
+                } elseif ($callback && is_callable($callback)) {
+                    throw new SingleCallbackNotAllowed();
                 }
             });
 

tests/JoinRelationshipTest.php

@@ -3,6 +3,7 @@
 namespace Kirschbaum\PowerJoins\Tests;
 
 use Exception;
+use Kirschbaum\PowerJoins\Exceptions\SingleCallbackNotAllowed;
 use Kirschbaum\PowerJoins\PowerJoinClause;
 use Kirschbaum\PowerJoins\Tests\Models\Category;
 use Kirschbaum\PowerJoins\Tests\Models\Comment;
@@ -271,6 +272,14 @@ public function test_join_belongs_to_many_with_callback()
         );
     }
 
+    /** @test */
+    public function test_single_callback_in_belongs_to_many_should_throw_exception()
+    {
+        $this->expectException(SingleCallbackNotAllowed::class);
+
+        User::query()->joinRelationship('groups', fn ($join) => $join->where('groups.name', 'Test'));
+    }
+
     /** @test */
     public function test_it_doesnt_join_the_same_relationship_twice()
     {