fix: return type of associate, dissociate and getChild methods of BelongsTo relations

CHANGELOG.md

@@ -6,6 +6,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [Unreleased]
 
+### Fixed
+
+- Return type of `associate`, `dissociate` and `getChild` methods of `BelongsTo` relations ([#633](https://github.com/nunomaduro/larastan/pull/633))
+
 ## [0.6.2] - 2020-07-30
 
 ### Fixed

src/Types/ModelRelationsDynamicMethodReturnTypeExtension.php

@@ -5,6 +5,7 @@
 namespace NunoMaduro\Larastan\Types;
 
 use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsTo;
 use Illuminate\Database\Eloquent\Relations\Relation;
 use NunoMaduro\Larastan\Concerns\HasContainer;
 use PhpParser\Node\Expr\MethodCall;
@@ -93,6 +94,15 @@ public function getTypeFromMethodCall(
             ->relationParserHelper
             ->findRelatedModelInRelationMethod($methodReflection);
 
+        $classReflection = $methodReflection->getDeclaringClass();
+
+        if ($returnType->isInstanceOf(BelongsTo::class)->yes()) {
+            return new GenericObjectType($returnType->getClassName(), [
+                new ObjectType($relatedModelClassName),
+                new ObjectType($classReflection->getName()),
+            ]);
+        }
+
         return new GenericObjectType($returnType->getClassName(), [new ObjectType($relatedModelClassName)]);
     }
 }

stubs/BelongsTo.stub

@@ -4,13 +4,20 @@ namespace Illuminate\Database\Eloquent\Relations;
 
 /**
  * @template TRelatedModel of \Illuminate\Database\Eloquent\Model
+ * @template TChildModel of \Illuminate\Database\Eloquent\Model
  * @extends Relation<TRelatedModel>
  */
 class BelongsTo extends Relation
 {
-    /** @phpstan-return TRelatedModel */
+    /** @phpstan-return TChildModel */
     public function associate();
 
+    /** @phpstan-return TChildModel */
+    public function dissociate();
+
+    /** @phpstan-return TChildModel */
+    public function getChild();
+
     /**
      * Get the results of the relationship.
      *

tests/Features/Models/Relations.php

@@ -135,15 +135,15 @@ public function it_doesnt_treat_whereHas_as_dynamic_where(): User
     }
 
     /**
-     * @phpstan-return BelongsTo<User>
+     * @phpstan-return BelongsTo<User, Account>
      */
     public function testRelationWithTrait(Account $account): BelongsTo
     {
         return $account->ownerRelation();
     }
 
     /**
-     * @phpstan-return BelongsTo<Account>
+     * @phpstan-return BelongsTo<Account, Account>
      */
     public function testRelationInTraitWithStaticClass(Account $account): BelongsTo
     {
@@ -156,7 +156,7 @@ public function testSameClassRelation(User $user): HasMany
         return $user->children();
     }
 
-    /** @phpstan-return BelongsTo<User> */
+    /** @phpstan-return BelongsTo<User, User> */
     public function testSameClassRelationWithGetClass(User $user): BelongsTo
     {
         return $user->parent();
@@ -202,3 +202,16 @@ public function testRelationCreateOnExistingModel(): Account
         return $this->user->accounts()->create();
     }
 }
+
+class Post extends Model
+{
+    public function author(): BelongsTo
+    {
+        return $this->belongsTo(User::class);
+    }
+
+    public function addUser(User $user): self
+    {
+        return $this->author()->associate($user);
+    }
+}