diff --git a/src/Hydrators/Base.php b/src/Hydrators/Base.php
index 1bd6d4d..7be44c6 100644
--- a/src/Hydrators/Base.php
+++ b/src/Hydrators/Base.php
@@ -9,6 +9,8 @@
 use Respect\Data\Hydrator;
 use SplObjectStorage;
 
+use function is_object;
+
 /** Base hydrator providing FK-to-entity wiring shared by all strategies */
 abstract class Base implements Hydrator
 {
@@ -25,6 +27,10 @@ protected function wireRelationships(SplObjectStorage $entities, EntityFactory $
                 }
 
                 foreach ($entitiesClone as $sub) {
+                    if ($sub === $instance) {
+                        continue;
+                    }
+
                     $tableName = (string) $entities[$sub]->name;
                     $primaryName = $style->identifier($tableName);
 
@@ -38,7 +44,16 @@ protected function wireRelationships(SplObjectStorage $entities, EntityFactory $
                     $v = $sub;
                 }
 
-                $entityFactory->set($instance, $field, $v);
+                if (!is_object($v)) {
+                    continue;
+                }
+
+                $relationName = $style->relationProperty($field);
+                if ($relationName === null) {
+                    continue;
+                }
+
+                $entityFactory->set($instance, $relationName, $v);
             }
         }
     }
diff --git a/src/Hydrators/Flat.php b/src/Hydrators/Flat.php
index 4b9e218..e2877cc 100644
--- a/src/Hydrators/Flat.php
+++ b/src/Hydrators/Flat.php
@@ -56,7 +56,7 @@ public function hydrate(
                 $value,
             );
 
-            if ($primaryName != $columnName) {
+            if ($primaryName != $columnName && !$this->isEntityBoundary($col, $raw)) {
                 continue;
             }
 
@@ -75,6 +75,12 @@ public function hydrate(
     /** Resolve the column name for a given reference (numeric index, namespaced key, etc.) */
     abstract protected function resolveColumnName(mixed $reference, mixed $raw): string;
 
+    /** Check if this column is the last one for the current entity (table boundary without PK) */
+    protected function isEntityBoundary(mixed $col, mixed $raw): bool
+    {
+        return false;
+    }
+
     /**
      * @param SplObjectStorage<object, Collection> $entities
      *
diff --git a/src/Styles/NorthWind.php b/src/Styles/NorthWind.php
index 562f376..da9c052 100644
--- a/src/Styles/NorthWind.php
+++ b/src/Styles/NorthWind.php
@@ -44,4 +44,14 @@ public function remoteFromIdentifier(string $name): string|null
     {
         return $this->isRemoteIdentifier($name) ? $this->singularToPlural(substr($name, 0, -2)) : null;
     }
+
+    public function relationProperty(string $field): string|null
+    {
+        return $this->isRemoteIdentifier($field) ? substr($field, 0, -2) : null;
+    }
+
+    public function isRelationProperty(string $name): bool
+    {
+        return !$this->isRemoteIdentifier($name) && $this->isRemoteIdentifier($name . 'ID');
+    }
 }
diff --git a/src/Styles/Standard.php b/src/Styles/Standard.php
index 87bb7fe..d278721 100644
--- a/src/Styles/Standard.php
+++ b/src/Styles/Standard.php
@@ -56,4 +56,14 @@ public function remoteFromIdentifier(string $name): string|null
     {
         return $this->isRemoteIdentifier($name) ? substr($name, 0, -3) : null;
     }
+
+    public function relationProperty(string $field): string|null
+    {
+        return $this->isRemoteIdentifier($field) ? substr($field, 0, -3) : null;
+    }
+
+    public function isRelationProperty(string $name): bool
+    {
+        return !$this->isRemoteIdentifier($name) && $this->isRemoteIdentifier($name . '_id');
+    }
 }
diff --git a/src/Styles/Stylable.php b/src/Styles/Stylable.php
index 9ef73bf..e135a03 100644
--- a/src/Styles/Stylable.php
+++ b/src/Styles/Stylable.php
@@ -22,5 +22,9 @@ public function remoteFromIdentifier(string $name): string|null;
 
     public function isRemoteIdentifier(string $name): bool;
 
+    public function relationProperty(string $remoteIdentifierField): string|null;
+
+    public function isRelationProperty(string $name): bool;
+
     public function composed(string $left, string $right): string;
 }
diff --git a/tests/AbstractMapperTest.php b/tests/AbstractMapperTest.php
index bca34d4..827dc43 100644
--- a/tests/AbstractMapperTest.php
+++ b/tests/AbstractMapperTest.php
@@ -243,12 +243,48 @@ public function hydrationWiresFkWithMatchingEntity(): void
 
         $comment = $mapper->comment->post->fetch();
         $this->assertIsObject($comment);
-        $post = $mapper->entityFactory->get($comment, 'post_id');
+        // FK stays as its original scalar value, never overwritten with an object
+        $fk = $mapper->entityFactory->get($comment, 'post_id');
+        $this->assertIsNotObject($fk);
+        $this->assertEquals(5, $fk);
+
+        // Related entity goes to the derived relation property
+        $post = $mapper->entityFactory->get($comment, 'post');
         $this->assertIsObject($post);
         $this->assertEquals(5, $mapper->entityFactory->get($post, 'id'));
         $this->assertEquals('Post', $mapper->entityFactory->get($post, 'title'));
     }
 
+    #[Test]
+    public function persistAfterHydrationPreservesFkAndIgnoresRelation(): void
+    {
+        $mapper = new InMemoryMapper();
+        $mapper->seed('comment', [
+            ['id' => 1, 'text' => 'Hello', 'post_id' => 5],
+        ]);
+        $mapper->seed('post', [
+            ['id' => 5, 'title' => 'Post'],
+        ]);
+
+        // Fetch with relationship — hydrates $comment->post
+        $comment = $mapper->comment->post->fetch();
+        $this->assertIsObject($mapper->entityFactory->get($comment, 'post'));
+
+        // Modify and persist
+        $mapper->entityFactory->set($comment, 'text', 'Updated');
+        $mapper->comment->persist($comment);
+        $mapper->flush();
+
+        // Re-fetch without relationship
+        $updated = $mapper->comment[1]->fetch();
+        $this->assertEquals('Updated', $mapper->entityFactory->get($updated, 'text'));
+
+        // FK stayed as scalar
+        $fk = $mapper->entityFactory->get($updated, 'post_id');
+        $this->assertIsNotObject($fk);
+        $this->assertEquals(5, $fk);
+    }
+
     #[Test]
     public function hydrationLeavesFkUnchangedWhenNoMatch(): void
     {
@@ -278,7 +314,9 @@ public function hydrationMatchesIntFkToStringPk(): void
 
         $comment = $mapper->comment->post->fetch();
         $this->assertIsObject($comment);
-        $post = $mapper->entityFactory->get($comment, 'post_id');
+        // FK stays as int, relation goes to derived property
+        $this->assertEquals(5, $mapper->entityFactory->get($comment, 'post_id'));
+        $post = $mapper->entityFactory->get($comment, 'post');
         $this->assertIsObject($post);
         $this->assertEquals('5', $mapper->entityFactory->get($post, 'id'));
     }
diff --git a/tests/Styles/AbstractStyleTest.php b/tests/Styles/AbstractStyleTest.php
index e962f96..a589a97 100644
--- a/tests/Styles/AbstractStyleTest.php
+++ b/tests/Styles/AbstractStyleTest.php
@@ -61,6 +61,16 @@ public function remoteFromIdentifier(string $name): string|null
             {
                 return null;
             }
+
+            public function relationProperty(string $field): string|null
+            {
+                return null;
+            }
+
+            public function isRelationProperty(string $name): bool
+            {
+                return false;
+            }
         };
     }
 
diff --git a/tests/Styles/CakePHP/CakePHPIntegrationTest.php b/tests/Styles/CakePHP/CakePHPIntegrationTest.php
index f0591bd..22de5b5 100644
--- a/tests/Styles/CakePHP/CakePHPIntegrationTest.php
+++ b/tests/Styles/CakePHP/CakePHPIntegrationTest.php
@@ -59,7 +59,7 @@ public function testFetchingAllEntityTyped(): void
 
         $categories = $mapper->post_categories->categories->fetch();
         $this->assertInstanceOf(PostCategory::class, $categories);
-        $this->assertInstanceOf(Category::class, $categories->category_id);
+        $this->assertInstanceOf(Category::class, $categories->category);
     }
 
     public function testFetchingAllEntityTypedNested(): void
@@ -67,8 +67,8 @@ public function testFetchingAllEntityTypedNested(): void
         $mapper = $this->mapper;
         $comment = $mapper->comments->posts->authors->fetchAll();
         $this->assertInstanceOf(Comment::class, $comment[0]);
-        $this->assertInstanceOf(Post::class, $comment[0]->post_id);
-        $this->assertInstanceOf(Author::class, $comment[0]->post_id->author_id);
+        $this->assertInstanceOf(Post::class, $comment[0]->post);
+        $this->assertInstanceOf(Author::class, $comment[0]->post->author);
     }
 
     public function testPersistingEntityTyped(): void
diff --git a/tests/Styles/CakePHP/Comment.php b/tests/Styles/CakePHP/Comment.php
index 2833d77..503d9f1 100644
--- a/tests/Styles/CakePHP/Comment.php
+++ b/tests/Styles/CakePHP/Comment.php
@@ -10,5 +10,7 @@ class Comment
 
     public mixed $post_id = null;
 
+    public mixed $post = null;
+
     public string|null $text = null;
 }
diff --git a/tests/Styles/CakePHP/Post.php b/tests/Styles/CakePHP/Post.php
index c5a76cb..a454e41 100644
--- a/tests/Styles/CakePHP/Post.php
+++ b/tests/Styles/CakePHP/Post.php
@@ -13,4 +13,6 @@ class Post
     public string|null $text = null;
 
     public mixed $author_id = null;
+
+    public mixed $author = null;
 }
diff --git a/tests/Styles/CakePHP/PostCategory.php b/tests/Styles/CakePHP/PostCategory.php
index 825dc62..6046004 100644
--- a/tests/Styles/CakePHP/PostCategory.php
+++ b/tests/Styles/CakePHP/PostCategory.php
@@ -11,4 +11,6 @@ class PostCategory
     public mixed $post_id = null;
 
     public mixed $category_id = null;
+
+    public mixed $category = null;
 }
diff --git a/tests/Styles/NorthWind/Comments.php b/tests/Styles/NorthWind/Comments.php
index 0d3fa47..2f93800 100644
--- a/tests/Styles/NorthWind/Comments.php
+++ b/tests/Styles/NorthWind/Comments.php
@@ -10,5 +10,7 @@ class Comments
 
     public mixed $PostID = null;
 
+    public mixed $Post = null;
+
     public string|null $Text = null;
 }
diff --git a/tests/Styles/NorthWind/NorthWindIntegrationTest.php b/tests/Styles/NorthWind/NorthWindIntegrationTest.php
index 19ff9d8..dbed67e 100644
--- a/tests/Styles/NorthWind/NorthWindIntegrationTest.php
+++ b/tests/Styles/NorthWind/NorthWindIntegrationTest.php
@@ -59,7 +59,7 @@ public function testFetchingAllEntityTyped(): void
 
         $categories = $mapper->PostCategories->Categories->fetch();
         $this->assertInstanceOf(PostCategories::class, $categories);
-        $this->assertInstanceOf(Categories::class, $categories->CategoryID);
+        $this->assertInstanceOf(Categories::class, $categories->Category);
     }
 
     public function testFetchingAllEntityTypedNested(): void
@@ -67,8 +67,8 @@ public function testFetchingAllEntityTypedNested(): void
         $mapper = $this->mapper;
         $comment = $mapper->Comments->Posts->Authors->fetchAll();
         $this->assertInstanceOf(Comments::class, $comment[0]);
-        $this->assertInstanceOf(Posts::class, $comment[0]->PostID);
-        $this->assertInstanceOf(Authors::class, $comment[0]->PostID->AuthorID);
+        $this->assertInstanceOf(Posts::class, $comment[0]->Post);
+        $this->assertInstanceOf(Authors::class, $comment[0]->Post->Author);
     }
 
     public function testPersistingEntityTyped(): void
diff --git a/tests/Styles/NorthWind/PostCategories.php b/tests/Styles/NorthWind/PostCategories.php
index 87421df..27cd528 100644
--- a/tests/Styles/NorthWind/PostCategories.php
+++ b/tests/Styles/NorthWind/PostCategories.php
@@ -11,4 +11,6 @@ class PostCategories
     public mixed $PostID = null;
 
     public mixed $CategoryID = null;
+
+    public mixed $Category = null;
 }
diff --git a/tests/Styles/NorthWind/Posts.php b/tests/Styles/NorthWind/Posts.php
index 2153ca6..a933e38 100644
--- a/tests/Styles/NorthWind/Posts.php
+++ b/tests/Styles/NorthWind/Posts.php
@@ -13,4 +13,6 @@ class Posts
     public string|null $Text = null;
 
     public mixed $AuthorID = null;
+
+    public mixed $Author = null;
 }
diff --git a/tests/Styles/NorthWindTest.php b/tests/Styles/NorthWindTest.php
index cbc448c..de3d2ec 100644
--- a/tests/Styles/NorthWindTest.php
+++ b/tests/Styles/NorthWindTest.php
@@ -93,4 +93,35 @@ public function testKeys(string $table, string $foreign): void
         $this->assertEquals($foreign, $this->style->identifier($table));
         $this->assertEquals($foreign, $this->style->remoteIdentifier($table));
     }
+
+    /** @return array<int, array<int, string>> */
+    public static function relationProvider(): array
+    {
+        return [
+            ['Post',   'PostID'],
+            ['Author', 'AuthorID'],
+            ['Tag',    'TagID'],
+            ['User',   'UserID'],
+        ];
+    }
+
+    #[DataProvider('relationProvider')]
+    public function testRelationProperty(string $relation, string $foreign): void
+    {
+        $this->assertEquals($relation, $this->style->relationProperty($foreign));
+        $this->assertNull($this->style->relationProperty($relation));
+    }
+
+    #[DataProvider('relationProvider')]
+    public function testIsRelationProperty(string $relation, string $foreign): void
+    {
+        $this->assertTrue($this->style->isRelationProperty($relation));
+        $this->assertFalse($this->style->isRelationProperty($foreign));
+    }
+
+    #[DataProvider('relationProvider')]
+    public function testForeignKeyIsNotRelationProperty(string $relation, string $foreign): void
+    {
+        $this->assertFalse($this->style->isRelationProperty($foreign));
+    }
 }
diff --git a/tests/Styles/Plural/Comment.php b/tests/Styles/Plural/Comment.php
index 1f70592..a70022d 100644
--- a/tests/Styles/Plural/Comment.php
+++ b/tests/Styles/Plural/Comment.php
@@ -10,5 +10,7 @@ class Comment
 
     public mixed $post_id = null;
 
+    public mixed $post = null;
+
     public string|null $text = null;
 }
diff --git a/tests/Styles/Plural/PluralIntegrationTest.php b/tests/Styles/Plural/PluralIntegrationTest.php
index 8e2bf39..8e7b148 100644
--- a/tests/Styles/Plural/PluralIntegrationTest.php
+++ b/tests/Styles/Plural/PluralIntegrationTest.php
@@ -59,7 +59,7 @@ public function testFetchingAllEntityTyped(): void
 
         $categories = $mapper->posts_categories->categories->fetch();
         $this->assertInstanceOf(PostCategory::class, $categories);
-        $this->assertInstanceOf(Category::class, $categories->category_id);
+        $this->assertInstanceOf(Category::class, $categories->category);
     }
 
     public function testFetchingAllEntityTypedNested(): void
@@ -67,8 +67,8 @@ public function testFetchingAllEntityTypedNested(): void
         $mapper = $this->mapper;
         $comment = $mapper->comments->posts->authors->fetchAll();
         $this->assertInstanceOf(Comment::class, $comment[0]);
-        $this->assertInstanceOf(Post::class, $comment[0]->post_id);
-        $this->assertInstanceOf(Author::class, $comment[0]->post_id->author_id);
+        $this->assertInstanceOf(Post::class, $comment[0]->post);
+        $this->assertInstanceOf(Author::class, $comment[0]->post->author);
     }
 
     public function testPersistingEntityTyped(): void
diff --git a/tests/Styles/Plural/Post.php b/tests/Styles/Plural/Post.php
index d8789ab..a29b5e7 100644
--- a/tests/Styles/Plural/Post.php
+++ b/tests/Styles/Plural/Post.php
@@ -13,4 +13,6 @@ class Post
     public string|null $text = null;
 
     public mixed $author_id = null;
+
+    public mixed $author = null;
 }
diff --git a/tests/Styles/Plural/PostCategory.php b/tests/Styles/Plural/PostCategory.php
index ea5b4fa..2e168de 100644
--- a/tests/Styles/Plural/PostCategory.php
+++ b/tests/Styles/Plural/PostCategory.php
@@ -11,4 +11,6 @@ class PostCategory
     public mixed $post_id = null;
 
     public mixed $category_id = null;
+
+    public mixed $category = null;
 }
diff --git a/tests/Styles/Sakila/Comment.php b/tests/Styles/Sakila/Comment.php
index 337e666..0e4afc1 100644
--- a/tests/Styles/Sakila/Comment.php
+++ b/tests/Styles/Sakila/Comment.php
@@ -10,5 +10,7 @@ class Comment
 
     public mixed $post_id = null;
 
+    public mixed $post = null;
+
     public string|null $text = null;
 }
diff --git a/tests/Styles/Sakila/Post.php b/tests/Styles/Sakila/Post.php
index 65e1473..ffaf836 100644
--- a/tests/Styles/Sakila/Post.php
+++ b/tests/Styles/Sakila/Post.php
@@ -13,4 +13,6 @@ class Post
     public string|null $text = null;
 
     public mixed $author_id = null;
+
+    public mixed $author = null;
 }
diff --git a/tests/Styles/Sakila/PostCategory.php b/tests/Styles/Sakila/PostCategory.php
index 70b6e80..86a1d11 100644
--- a/tests/Styles/Sakila/PostCategory.php
+++ b/tests/Styles/Sakila/PostCategory.php
@@ -11,4 +11,6 @@ class PostCategory
     public mixed $post_id = null;
 
     public mixed $category_id = null;
+
+    public mixed $category = null;
 }
diff --git a/tests/Styles/Sakila/SakilaIntegrationTest.php b/tests/Styles/Sakila/SakilaIntegrationTest.php
index 04645cd..57a391e 100644
--- a/tests/Styles/Sakila/SakilaIntegrationTest.php
+++ b/tests/Styles/Sakila/SakilaIntegrationTest.php
@@ -59,7 +59,7 @@ public function testFetchingAllEntityTyped(): void
 
         $categories = $mapper->post_category->category->fetch();
         $this->assertInstanceOf(PostCategory::class, $categories);
-        $this->assertInstanceOf(Category::class, $categories->category_id);
+        $this->assertInstanceOf(Category::class, $categories->category);
     }
 
     public function testFetchingAllEntityTypedNested(): void
@@ -67,8 +67,8 @@ public function testFetchingAllEntityTypedNested(): void
         $mapper = $this->mapper;
         $comment = $mapper->comment->post->author->fetchAll();
         $this->assertInstanceOf(Comment::class, $comment[0]);
-        $this->assertInstanceOf(Post::class, $comment[0]->post_id);
-        $this->assertInstanceOf(Author::class, $comment[0]->post_id->author_id);
+        $this->assertInstanceOf(Post::class, $comment[0]->post);
+        $this->assertInstanceOf(Author::class, $comment[0]->post->author);
     }
 
     public function testPersistingEntityTyped(): void
diff --git a/tests/Styles/StandardTest.php b/tests/Styles/StandardTest.php
index 2ac49b2..369dc26 100644
--- a/tests/Styles/StandardTest.php
+++ b/tests/Styles/StandardTest.php
@@ -93,4 +93,24 @@ public function testForeign(string $table, string $foreign): void
         $this->assertEquals($table, $this->style->remoteFromIdentifier($foreign));
         $this->assertEquals($foreign, $this->style->remoteIdentifier($table));
     }
+
+    #[DataProvider('foreignProvider')]
+    public function testRelationProperty(string $table, string $foreign): void
+    {
+        $this->assertEquals($table, $this->style->relationProperty($foreign));
+        $this->assertNull($this->style->relationProperty($table));
+    }
+
+    #[DataProvider('foreignProvider')]
+    public function testIsRelationProperty(string $table, string $foreign): void
+    {
+        $this->assertTrue($this->style->isRelationProperty($table));
+        $this->assertFalse($this->style->isRelationProperty($foreign));
+    }
+
+    #[DataProvider('foreignProvider')]
+    public function testForeignKeyIsNotRelationProperty(string $table, string $foreign): void
+    {
+        $this->assertFalse($this->style->isRelationProperty($foreign));
+    }
 }