diff --git a/src/Behaviours/Cacheable.php b/src/Behaviours/Cacheable.php
index 5d908f8..cfbc0f5 100644
--- a/src/Behaviours/Cacheable.php
+++ b/src/Behaviours/Cacheable.php
@@ -3,8 +3,6 @@
 
 use Closure;
 use Illuminate\Database\Eloquent\Model;
-use Illuminate\Support\Facades\DB;
-use Illuminate\Support\Str;
 
 /**
  * The cacheable trait is concerned with the related models.
diff --git a/src/Behaviours/CountCache/CountCache.php b/src/Behaviours/CountCache/CountCache.php
index 8e324ee..5da735b 100644
--- a/src/Behaviours/CountCache/CountCache.php
+++ b/src/Behaviours/CountCache/CountCache.php
@@ -28,7 +28,8 @@ public function update(): void
         $this->apply(function(CacheConfig $config) {
             $foreignKey = $config->foreignKeyName($this->model);
 
-            if (!$this->model->getOriginal($foreignKey) || $this->model->$foreignKey === $this->model->getOriginal($foreignKey)) return;
+            // We only need to do anything if the foreign key was changed.
+            if (!$this->model->wasChanged($foreignKey)) return;
 
             // for the minus operation, we first have to get the model that is no longer associated with this one.
             $originalRelatedModel = $config->emptyRelatedModel($this->model)->find($this->model->getOriginal($foreignKey));
diff --git a/src/Behaviours/SumCache/SumCache.php b/src/Behaviours/SumCache/SumCache.php
index 6fb9e99..d708669 100644
--- a/src/Behaviours/SumCache/SumCache.php
+++ b/src/Behaviours/SumCache/SumCache.php
@@ -31,14 +31,14 @@ public function rebuild(): void
     public function increase(): void
     {
         $this->apply(function(CacheConfig $config) {
-            $this->updateCacheValue($config->relatedModel($this->model), $config, $this->model->{$config->sourceField});
+            $this->updateCacheValue($config->relatedModel($this->model), $config, (int) $this->model->{$config->sourceField});
         });
     }
 
     public function decrease(): void
     {
         $this->apply(function(CacheConfig $config) {
-            $this->updateCacheValue($config->relatedModel($this->model), $config, -$this->model->{$config->sourceField});
+            $this->updateCacheValue($config->relatedModel($this->model), $config, -(int) $this->model->{$config->sourceField});
         });
     }
 
diff --git a/src/Behaviours/SumCache/Summable.php b/src/Behaviours/SumCache/Summable.php
index 007f503..607f9f9 100644
--- a/src/Behaviours/SumCache/Summable.php
+++ b/src/Behaviours/SumCache/Summable.php
@@ -13,7 +13,11 @@ interface Summable
      *
      * Of course, if you want to customise the field saving the total as well, you can do that too:
      *
-     * ['order' => ['amount' => 'total_amount']].
+     * ['relationshp' => ['aggregate_field' => 'source_field']]
+     *
+     * In real-world terms:
+     *
+     * ['order' => ['total_amount' => 'amount']]
      *
      * By default, the sum cache will take the source field, and add "_total" to it on the related model.
      *
diff --git a/tests/Acceptance/AcceptanceTestCase.php b/tests/Acceptance/AcceptanceTestCase.php
index 6c6dca1..939f5d4 100644
--- a/tests/Acceptance/AcceptanceTestCase.php
+++ b/tests/Acceptance/AcceptanceTestCase.php
@@ -33,8 +33,8 @@ private function migrate()
     {
         Schema::create('users', function (Blueprint $table) {
             $table->increments('id');
-            $table->string('first_name');
-            $table->string('last_name');
+            $table->string('first_name')->nullable();
+            $table->string('last_name')->nullable();
             $table->string('slug')->nullable();
             $table->integer('comment_count')->default(0);
             $table->integer('post_count')->default(0);
@@ -43,6 +43,7 @@ private function migrate()
 
         Schema::create('posts', function (Blueprint $table) {
             $table->increments('id');
+            $table->integer('category_id')->nullable();
             $table->integer('user_id')->nullable();
             $table->string('slug')->nullable();
             $table->integer('comment_count')->default(0);
@@ -69,5 +70,12 @@ private function migrate()
             $table->integer('amount');
             $table->timestamps();
         });
+
+        Schema::create('categories', function (Blueprint $table) {
+            $table->increments('id');
+            $table->integer('post_count')->default(0);
+            $table->integer('total_comments')->default(0);
+            $table->timestamps();
+        });
     }
 }
diff --git a/tests/Acceptance/ChainedAggregatesTest.php b/tests/Acceptance/ChainedAggregatesTest.php
new file mode 100644
index 0000000..6a6d65a
--- /dev/null
+++ b/tests/Acceptance/ChainedAggregatesTest.php
@@ -0,0 +1,18 @@
+<?php
+
+namespace Tests\Acceptance;
+
+use Tests\Acceptance\Models\Category;
+use Tests\Acceptance\Models\Comment;
+
+class ChainedAggregatesTest extends AcceptanceTestCase
+{
+    function test_aggregateDependentsAreUpdated()
+    {
+        // Comment will create a user, and a post - the post created will bubble up to category and update it as well.
+        Comment::factory()->create();
+
+        $this->assertSame(1, Category::first()->postCount);
+        $this->assertSame(1, Category::first()->totalComments);
+    }
+}
\ No newline at end of file
diff --git a/tests/Acceptance/CountCacheTest.php b/tests/Acceptance/CountCacheTest.php
index a296aab..e246c48 100644
--- a/tests/Acceptance/CountCacheTest.php
+++ b/tests/Acceptance/CountCacheTest.php
@@ -1,76 +1,49 @@
 <?php
 namespace Tests\Acceptance;
 
+use Tests\Acceptance\Models\Category;
 use Tests\Acceptance\Models\Comment;
 use Tests\Acceptance\Models\Post;
 use Tests\Acceptance\Models\User;
 
 class CountCacheTest extends AcceptanceTestCase
 {
-    private $data = [];
-
-    public function init()
-    {
-        $this->data = $this->setupUserAndPost();
-    }
-
     function test_userHasASinglePostCount()
     {
-        $user = User::first();
+        $user = User::factory()->create();
 
-        $this->assertEquals(1, $user->postCount);
+        Post::factory()->for($user)->create();
+
+        $this->assertEquals(1, $user->fresh()->postCount);
     }
 
     function test_whenRelatedModelsAreSwitchedBothCountCachesAreUpdated()
     {
-        $post = new Post;
-        $post->userId = $this->data['user']->id;
-        $post->save();
-
-        $comment = new Comment;
-        $comment->userId = $this->data['user']->id;
-        $comment->postId = $this->data['post']->id;
-        $comment->save();
+        $user1 = User::factory()->create();
+        $user2 = User::factory()->create();
+        $posts = Post::factory()->count(2)->for($user1)->create();
+        $comment = Comment::factory()->for($user1)->for($posts->first())->create();
 
-        $this->assertEquals(2, User::first()->postCount);
-        $this->assertEquals(1, User::first()->commentCount);
-        $this->assertEquals(1, Post::first()->commentCount);
+        $this->assertEquals(2, $user1->fresh()->postCount);
+        $this->assertEquals(1, $user1->fresh()->commentCount);
+        $this->assertEquals(1, $posts->first()->fresh()->commentCount);
 
         $comment = $comment->fresh();
-        $comment->postId = $post->id;
+        $comment->userId = $user2->id;
         $comment->save();
 
-        $this->assertEquals(0, $this->data['post']->fresh()->commentCount);
-        $this->assertEquals(1, $post->fresh()->commentCount);
+        $this->assertEquals(0, $user1->fresh()->commentCount);
+        $this->assertEquals(1, $user2->fresh()->commentCount);
     }
 
-    public function testItCanHandleNegativeCounts()
+    public function testItCanHandleModelRestoration()
     {
-        $post = new Post;
-        $post->userId = $this->data['user']->id;
-        $post->save();
+        $post = Post::factory()->create();
 
-        $comment = new Comment;
-        $comment->userId = $this->data['user']->id;
-        $comment->postId = $this->data['post']->id;
-        $comment->save();
+        $comment = Comment::factory()->for($post)->create();
         $comment->delete();
         $comment->restore();
 
-        $this->assertEquals(1, Post::first()->commentCount);
-    }
-
-    private function setupUserAndPost()
-    {
-        $user = new User;
-        $user->firstName = 'Kirk';
-        $user->lastName = 'Bushell';
-        $user->save();
-
-        $post = new Post;
-        $post->userId = $user->id;
-        $post->save();
-
-        return compact('user', 'post');
+        $this->assertEquals(1, $post->fresh()->commentCount);
     }
 }
diff --git a/tests/Acceptance/Models/Category.php b/tests/Acceptance/Models/Category.php
new file mode 100644
index 0000000..cf0c985
--- /dev/null
+++ b/tests/Acceptance/Models/Category.php
@@ -0,0 +1,19 @@
+<?php
+
+namespace Tests\Acceptance\Models;
+
+use Eloquence\Behaviours\CamelCased;
+use Illuminate\Database\Eloquent\Factories\Factory;
+use Illuminate\Database\Eloquent\Factories\HasFactory;
+use Illuminate\Database\Eloquent\Model;
+
+class Category extends Model
+{
+    use CamelCased;
+    use HasFactory;
+
+    protected static function newFactory(): Factory
+    {
+        return CategoryFactory::new();
+    }
+}
diff --git a/tests/Acceptance/Models/CategoryFactory.php b/tests/Acceptance/Models/CategoryFactory.php
new file mode 100644
index 0000000..1dff59c
--- /dev/null
+++ b/tests/Acceptance/Models/CategoryFactory.php
@@ -0,0 +1,15 @@
+<?php
+
+namespace Tests\Acceptance\Models;
+
+use Illuminate\Database\Eloquent\Factories\Factory;
+
+class CategoryFactory extends Factory
+{
+    protected $model = Category::class;
+
+    public function definition()
+    {
+        return [];
+    }
+}
\ No newline at end of file
diff --git a/tests/Acceptance/Models/Comment.php b/tests/Acceptance/Models/Comment.php
index ae4a4c7..e534aac 100644
--- a/tests/Acceptance/Models/Comment.php
+++ b/tests/Acceptance/Models/Comment.php
@@ -4,6 +4,8 @@
 use Eloquence\Behaviours\CountCache\Countable;
 use Eloquence\Behaviours\CountCache\HasCounts;
 use Eloquence\Behaviours\CamelCased;
+use Illuminate\Database\Eloquent\Factories\Factory;
+use Illuminate\Database\Eloquent\Factories\HasFactory;
 use Illuminate\Database\Eloquent\Model;
 use Illuminate\Database\Eloquent\Relations\BelongsTo;
 use Illuminate\Database\Eloquent\SoftDeletes;
@@ -12,8 +14,14 @@ class Comment extends Model implements Countable
 {
     use CamelCased;
     use HasCounts;
+    use HasFactory;
     use SoftDeletes;
 
+    protected $fillable = [
+        'user_id',
+        'post_id',
+    ];
+
     public function post(): BelongsTo
     {
         return $this->belongsTo(Post::class);
@@ -28,4 +36,9 @@ public function countedBy(): array
     {
         return ['post', 'user'];
     }
+
+    protected static function newFactory(): Factory
+    {
+        return CommentFactory::new();
+    }
 }
diff --git a/tests/Acceptance/Models/CommentFactory.php b/tests/Acceptance/Models/CommentFactory.php
new file mode 100644
index 0000000..8337cf2
--- /dev/null
+++ b/tests/Acceptance/Models/CommentFactory.php
@@ -0,0 +1,18 @@
+<?php
+
+namespace Tests\Acceptance\Models;
+
+use Illuminate\Database\Eloquent\Factories\Factory;
+
+class CommentFactory extends Factory
+{
+    protected $model = Comment::class;
+
+    public function definition()
+    {
+        return [
+            'post_id' => Post::factory(),
+            'user_id' => User::factory(),
+        ];
+    }
+}
\ No newline at end of file
diff --git a/tests/Acceptance/Models/Item.php b/tests/Acceptance/Models/Item.php
index 41f9f02..4658e98 100644
--- a/tests/Acceptance/Models/Item.php
+++ b/tests/Acceptance/Models/Item.php
@@ -4,12 +4,15 @@
 use Eloquence\Behaviours\SumCache\HasSums;
 use Eloquence\Behaviours\CamelCased;
 use Eloquence\Behaviours\SumCache\Summable;
+use Illuminate\Database\Eloquent\Factories\Factory;
+use Illuminate\Database\Eloquent\Factories\HasFactory;
 use Illuminate\Database\Eloquent\Model;
 
 class Item extends Model implements Summable
 {
     use CamelCased;
     use HasSums;
+    use HasFactory;
 
     public function summedBy(): array
     {
@@ -20,4 +23,9 @@ public function order()
     {
         return $this->belongsTo(Order::class);
     }
+
+    protected static function newFactory(): Factory
+    {
+        return ItemFactory::new();
+    }
 }
diff --git a/tests/Acceptance/Models/ItemFactory.php b/tests/Acceptance/Models/ItemFactory.php
new file mode 100644
index 0000000..4bf070e
--- /dev/null
+++ b/tests/Acceptance/Models/ItemFactory.php
@@ -0,0 +1,15 @@
+<?php
+
+namespace Tests\Acceptance\Models;
+
+use Illuminate\Database\Eloquent\Factories\Factory;
+
+class ItemFactory extends Factory
+{
+    protected $model = Item::class;
+    
+    public function definition()
+    {
+        // TODO: Implement definition() method.
+    }
+}
\ No newline at end of file
diff --git a/tests/Acceptance/Models/Order.php b/tests/Acceptance/Models/Order.php
index f652f2d..8250a45 100644
--- a/tests/Acceptance/Models/Order.php
+++ b/tests/Acceptance/Models/Order.php
@@ -2,14 +2,22 @@
 namespace Tests\Acceptance\Models;
 
 use Eloquence\Behaviours\CamelCased;
+use Illuminate\Database\Eloquent\Factories\Factory;
+use Illuminate\Database\Eloquent\Factories\HasFactory;
 use Illuminate\Database\Eloquent\Model;
 
 class Order extends Model
 {
     use CamelCased;
+    use HasFactory;
 
     public function items()
     {
         return $this->hasMany(Item::class);
     }
+
+    protected static function newFactory(): Factory
+    {
+        return OrderFactory::new();
+    }
 }
diff --git a/tests/Acceptance/Models/OrderFactory.php b/tests/Acceptance/Models/OrderFactory.php
new file mode 100644
index 0000000..4e4a04d
--- /dev/null
+++ b/tests/Acceptance/Models/OrderFactory.php
@@ -0,0 +1,15 @@
+<?php
+
+namespace Tests\Acceptance\Models;
+
+use Illuminate\Database\Eloquent\Factories\Factory;
+
+class OrderFactory extends Factory
+{
+    protected $model = Order::class;
+    
+    public function definition()
+    {
+        // TODO: Implement definition() method.
+    }
+}
\ No newline at end of file
diff --git a/tests/Acceptance/Models/Post.php b/tests/Acceptance/Models/Post.php
index a9319f3..9b31378 100644
--- a/tests/Acceptance/Models/Post.php
+++ b/tests/Acceptance/Models/Post.php
@@ -5,14 +5,25 @@
 use Eloquence\Behaviours\CountCache\HasCounts;
 use Eloquence\Behaviours\CamelCased;
 use Eloquence\Behaviours\Sluggable;
+use Eloquence\Behaviours\SumCache\HasSums;
+use Eloquence\Behaviours\SumCache\Summable;
+use Illuminate\Database\Eloquent\Factories\Factory;
+use Illuminate\Database\Eloquent\Factories\HasFactory;
 use Illuminate\Database\Eloquent\Model;
 use Illuminate\Database\Eloquent\Relations\BelongsTo;
 
-class Post extends Model implements Countable
+class Post extends Model implements Countable, Summable
 {
     use CamelCased;
     use Sluggable;
     use HasCounts;
+    use HasFactory;
+    use HasSums;
+
+    protected $fillable = [
+        'user_id',
+        'category_id',
+    ];
 
     public function user(): BelongsTo
     {
@@ -21,11 +32,26 @@ public function user(): BelongsTo
 
     public function countedBy(): array
     {
-        return ['user'];
+        return ['user', 'category'];
     }
 
     public function slugStrategy()
     {
         return 'id';
     }
+
+    public function category(): BelongsTo
+    {
+        return $this->belongsTo(Category::class);
+    }
+
+    public function summedBy(): array
+    {
+        return ['category' => ['total_comments' => 'comment_count']];
+    }
+
+    protected static function newFactory(): Factory
+    {
+        return PostFactory::new();
+    }
 }
diff --git a/tests/Acceptance/Models/PostFactory.php b/tests/Acceptance/Models/PostFactory.php
new file mode 100644
index 0000000..b46c77b
--- /dev/null
+++ b/tests/Acceptance/Models/PostFactory.php
@@ -0,0 +1,18 @@
+<?php
+
+namespace Tests\Acceptance\Models;
+
+use Illuminate\Database\Eloquent\Factories\Factory;
+
+class PostFactory extends Factory
+{
+    protected $model = Post::class;
+    
+    public function definition()
+    {
+        return [
+            'category_id' => Category::factory(),
+            'user_id' => User::factory(),
+        ];
+    }
+}
\ No newline at end of file
diff --git a/tests/Acceptance/Models/User.php b/tests/Acceptance/Models/User.php
index e53295d..0a91b6b 100644
--- a/tests/Acceptance/Models/User.php
+++ b/tests/Acceptance/Models/User.php
@@ -3,15 +3,23 @@
 
 use Eloquence\Behaviours\CamelCased;
 use Eloquence\Behaviours\Sluggable;
+use Illuminate\Database\Eloquent\Factories\Factory;
+use Illuminate\Database\Eloquent\Factories\HasFactory;
 use Illuminate\Database\Eloquent\Model;
 
 class User extends Model
 {
     use CamelCased;
+    use HasFactory;
     use Sluggable;
 
     public function slugStrategy()
     {
         return ['firstName', 'lastName'];
     }
+
+    protected static function newFactory(): Factory
+    {
+        return UserFactory::new();
+    }
 }
diff --git a/tests/Acceptance/Models/UserFactory.php b/tests/Acceptance/Models/UserFactory.php
new file mode 100644
index 0000000..357e7f1
--- /dev/null
+++ b/tests/Acceptance/Models/UserFactory.php
@@ -0,0 +1,18 @@
+<?php
+
+namespace Tests\Acceptance\Models;
+
+use Illuminate\Database\Eloquent\Factories\Factory;
+
+class UserFactory extends Factory
+{
+    protected $model = User::class;
+    
+    public function definition()
+    {
+        return [
+            'firstName' => fake()->firstName(),
+            'lastName' => fake()->lastName(),
+        ];
+    }
+}
\ No newline at end of file
diff --git a/tests/Acceptance/SluggedTest.php b/tests/Acceptance/SluggedTest.php
index 7a4be28..d01a4e8 100644
--- a/tests/Acceptance/SluggedTest.php
+++ b/tests/Acceptance/SluggedTest.php
@@ -8,24 +8,14 @@ class SluggedTest extends AcceptanceTestCase
 {
     function test_slugsCanBeGeneratedWithCustomStrategy()
     {
-        $user = new User;
-        $user->firstName = 'Kirk';
-        $user->lastName = 'Bushell';
-        $user->save();
+        $user = User::factory(['firstName' => 'Kirk', 'lastName' => 'Bushell'])->create();
 
         $this->assertEquals('kirk-bushell', (string) $user->slug);
     }
 
     function test_slugsCanBeGeneratedUsingRandomValues()
     {
-        $user = new User;
-        $user->firstName = 'Kirk';
-        $user->lastName = 'Bushell';
-        $user->save();
-
-        $post = new Post;
-        $post->userId = $user->id;
-        $post->save();
+        $post = Post::factory()->create();
 
         $this->assertMatchesRegularExpression('/^[a-z0-9]{8}$/i', (string) $post->slug);
     }
diff --git a/tests/Acceptance/SumCacheTest.php b/tests/Acceptance/SumCacheTest.php
index 9e80f42..70a1ecf 100644
--- a/tests/Acceptance/SumCacheTest.php
+++ b/tests/Acceptance/SumCacheTest.php
@@ -6,7 +6,7 @@
 
 class SumCacheTest extends AcceptanceTestCase
 {
-    private $data = [];
+    private array $data = [];
 
     public function init()
     {