Handle through-self-relation existence queries

src/HasManyDeep.php

@@ -2,6 +2,7 @@
 
 namespace Staudenmeir\EloquentHasManyDeep;
 
+use Exception;
 use Illuminate\Contracts\Pagination\Paginator;
 use Illuminate\Database\Eloquent\Builder;
 use Illuminate\Database\Eloquent\Model;
@@ -288,6 +289,28 @@ public function chunk($count, callable $callback)
      */
     public function getRelationExistenceQuery(Builder $query, Builder $parentQuery, $columns = ['*'])
     {
+        foreach ($this->throughParents as $throughParent) {
+            if ($throughParent->getTable() === $parentQuery->getQuery()->from) {
+                if (!in_array(HasTableAlias::class, class_uses_recursive($throughParent))) {
+                    $traitClass = HasTableAlias::class;
+                    $throughParentClass = get_class($throughParent);
+
+                    throw new Exception(
+                        <<<EOT
+This query requires an additional trait. Please add the $traitClass trait to $throughParentClass.
+See https://github.com/staudenmeir/eloquent-has-many-deep/issues/137 for details.
+EOT
+                    );
+                }
+
+                $table = $throughParent->getTable() . ' as ' . $this->getRelationCountHash();
+
+                $throughParent->setTable($table);
+
+                break;
+            }
+        }
+
         $query = parent::getRelationExistenceQuery($query, $parentQuery, $columns);
 
         if (is_array($this->foreignKeys[0])) {
@@ -309,7 +332,9 @@ public function getRelationExistenceQuery(Builder $query, Builder $parentQuery,
      */
     public function getRelationExistenceQueryForSelfRelation(Builder $query, Builder $parentQuery, $columns = ['*'])
     {
-        $query->from($query->getModel()->getTable().' as '.$hash = $this->getRelationCountHash());
+        $hash = $this->getRelationCountHash();
+
+        $query->from($query->getModel()->getTable().' as '.$hash);
 
         $this->performJoin($query);
 

tests/HasManyDeepTest.php

@@ -10,6 +10,7 @@
 use Tests\Models\RoleUser;
 use Tests\Models\Tag;
 use Tests\Models\User;
+use Tests\Models\UserWithAliasTrait;
 
 class HasManyDeepTest extends TestCase
 {
@@ -174,6 +175,20 @@ public function testExistenceQueryForSelfRelationWithLeadingMorphMany()
         $this->assertEquals([21, 23], $posts->pluck('id')->all());
     }
 
+    public function testExistenceQueryForThroughSelfRelation()
+    {
+        $users = UserWithAliasTrait::withCount('teamPosts')->get();
+
+        $this->assertEquals([2, 2, 1], $users->pluck('team_posts_count')->all());
+    }
+
+    public function testExistenceQueryForThroughSelfRelationWithoutAliasTrait()
+    {
+        $this->expectExceptionMessageMatches('/' . preg_quote(User::class) . '/');
+
+        User::withCount('teamPosts')->get();
+    }
+
     public function testPaginate()
     {
         $comments = Country::first()->comments()

tests/Models/User.php

@@ -42,4 +42,9 @@ public function tagsFromRelations()
     {
         return $this->hasManyDeepFromRelations($this->posts(), (new Post())->tags());
     }
+
+    public function teamPosts()
+    {
+        return $this->hasManyDeep(Post::class, [Team::class, static::class], ['id', null, 'user_id'], ['team_id']);
+    }
 }

tests/Models/UserWithAliasTrait.php

@@ -0,0 +1,12 @@
+<?php
+
+namespace Tests\Models;
+
+use Staudenmeir\EloquentHasManyDeep\HasTableAlias;
+
+class UserWithAliasTrait extends User
+{
+    use HasTableAlias;
+
+    protected $table = 'users';
+}