违反完整性约束：1452 无法添加或更新子行：外键约束失败（Laravel 应用程序）

Question

我的 laravel 应用程序出现此错误。

这些是表格：

Post

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

类别

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();
});

外键

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');
});

这是我的模型

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';
}

这里是控制器

商店类别：

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

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

商店post

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!');
    }

有这个错误

SQLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails (the_film_corner.tfc_categories, CONSTRAINT categories_id_foreign FOREIGN KEY (id) REFERENCES tfc_post_category (cat_id) ON DELETE CASCADE) (SQL: insert into tfc_categories (name, updated_at, created_at) values (News, 2017-02-26 14:51:15, 2017-02-26 14:51:15))

谢谢

Answer 1

你添加的外键有误table:

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');
});

那么...

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');
    }
}

您可以按照 Laravel 的官方指南找到更多信息：

https://laravel.com/docs/5.4/eloquent-relationships#one-to-many

Answer 2

错误说明了一切。使用此设置，在将行插入 tfc_categories 之前，列 id 的值必须存在于 table tfc_post_category 的列 cat_id 中。如果不是，则您违反了失败消息中提到的约束。

但我猜您希望一列引用另一列，反之亦然。

违反完整性约束：1452 无法添加或更新子行：外键约束失败（Laravel 应用程序）

Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails (Laravel Application)

mysql

foreign-keys

laravel

laravel-5.4