完整性約束違規：1452無法添加或更新子行：外鍵約束失敗（Laravel應用程序）

Question

我在我的laravel應用程序中遇到此錯誤。

這些都是表：

後

Schema::create('posts', function (Blueprint $table) { 
     $table->increments('id'); 
     $table->string('title'); 
     $table->text('content'); 
     $table->timestamps(); 
     $table->integer('user_id')->unsigned(); 
}); 

分類

Schema::create('categories', function (Blueprint $table) { 
     $table->increments('id'); 
     $table->string('name'); 
     $table->timestamps(); 
}); 

Post_Category

Schema::create('post_category', function (Blueprint $table) { 
     $table->integer('post_id')->unsigned()->unique()->nullable(); 
     $table->integer('cat_id')->unsigned()->unique()->nullable(); 
     $table->timestamps(); 
}); 

外鍵

Schema::table('posts', function (Blueprint $table) { 
     $table->foreign('id')->references('post_id')->on('post_category')->onDelete('cascade'); 
}); 

Schema::table('categories', function (Blueprint $table) { 
     $table->foreign('id')->references('cat_id')->on('post_category')->onDelete('cascade'); 
}); 

這裏我的模型

class Categorie extends Model 
{ 
    protected $table = 'categories'; 

    public function posts() { 
     return $this->hasMany('App\PostCategory'); 
    } 
} 

...

class Post extends Model 
{ 
    public function author() { 
     return $this->belongsTo('App\User', 'user_id'); 
    } 

    public function featuredImage() { 
     return $this->belongsTo('App\Media', 'media_id'); 
    } 

    public function categories() { 
     return $this->hasMany('App\PostCategory'); 
    } 
} 

...

class PostCategory extends Model 
{ 
    protected $table = 'post_category'; 
} 

這裏控制器

店鋪分類：

public function store(StoreCategory $request) 
    { 
     $category = new Categorie; 
     $category->name = $request->input('name'); 
     $category->save(); 

     return redirect('/admin/categories')->with('status', 'New category created!'); 
    } 

店後

public function store(StorePost $request) 
    { 
     $post = new Post; 
     $post->title = $request->input('title'); 
     $post->content = $request->input('content'); 
     $post->media_id = $request->input('media_id'); 
     $post->user_id = $request->input('user_id'); 
     $post->save(); 

     return redirect('/admin/posts')->with('status', 'New post created!'); 
    } 

有了這個錯誤

SQLSTATE [2300 0]：完整性約束違規：1452無法添加或更新子行：外鍵約束失敗（the_film_corner。 tfc_categories，約束categories_id_foreign外鍵（id）參考文獻tfc_post_category（cat_id）ON DELETE CASCADE）（SQL：插入tfc_categories（name，updated_at，created_at）值（新聞，2017年2月26日14時51分15秒，2017-02- 26 14時51分15秒））

感謝

Answer 1

你在錯誤的表添加外鍵：

Schema::table('post_category', function(Blueprint $table) { 
    $table->foreign('post_id')->references('id')->on('post')->onDelete('cascade'); 
    $table->foreign('category_id')->references('id')->on('category')->onDelete('cascade'); 

}）;

則...

class Categorie extends Model 
{ 
    protected $table = 'categories'; 

    public function posts() { 
     return $this->belongsToMany('App\Category'); 

    // Or more specifically 
    return $this->belongsToMany('App\Category', 'post_category', 'id', 'post_id'); 
    } 
} 

class Post extends Model 
{ 
    // ... 

    public function categories() { 
     return $this->belongsToMany('App\Category'); 

     // Or more specifically 
     return $this->belongsToMany('App\Category', 'post_category', 'id', 'category_id'); 
    } 
} 

您可以找到以下官方指南的詳細信息：https://laravel.com/docs/5.4/eloquent-relationships#one-to-many

Answer 2

錯誤說明了一切。通過此設置，在將行插入tfc_categories之前，id列的值必須存在於表tfc_post_category的列cat_id中。如果沒有，則違反了失敗消息中提到的約束條件。

但我寧願猜你想要一列來引用另一列，反之亦然。