Laravel: 使用工厂函数创建外键时出现错误

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Laravel: 使用工厂函数创建外键时出现错误

我有以下迁移（用于一个透视表）：

        Schema::create('category_news', function (Blueprint $table) {
            $table->id();
            $table->timestamps();
            $table->unsignedBigInteger('category_id');
            $table->unsignedBigInteger('news_id');
            $table->unique(['category_id', 'news_id']);
            $table->foreign('news_id')->references('id')->on('news')->onDelete('cascade');
            $table->foreign('category_id')->references('id')->on('categories')->onDelete('cascade');
        });

我想用一些虚拟数据填充该表 - 为此，我创建了以下工厂：

$factory->define(CategoryNews::class, function (Faker $faker) {
  return [
    'category_id' => $faker->numberBetween($min = 1, $max = 35),
    'news_id' => $faker->numberBetween($min = 1, $max = 150)
  ];
});

然而，当我运行以下命令：php artisan migrate:fresh --seed，我得到以下错误：

 Illuminate\Database\QueryException
  SQLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails (`startup-reporter`.`category_news`, CONSTRAINT `category_news_news_id_foreign` FOREIGN KEY (`news_id`) REFERENCES `news` (`id`) ON DELETE CASCADE) (SQL: insert into `category_news` (`category_id`, `news_id`, `updated_at`, `created_at`) values (16, 13, 2020-03-31 10:44:04, 2020-03-31 10:44:04))
  at C:\laragon\www\startup-reporter\vendor\laravel\framework\src\Illuminate\Database\Connection.php:669
    665|         // If an exception occurs when attempting to run a query, we'll format the error
    666|         // message to include the bindings with SQL, which will make this exception a
    667|         // lot more helpful to the developer instead of just the database's errors.
    668|         catch (Exception $e) {
  > 669|             throw new QueryException(
    670|                 $query, $this->prepareBindings($bindings), $e
    671|             );
    672|         }
    673|
  1   C:\laragon\www\startup-reporter\vendor\laravel\framework\src\Illuminate\Database\Connection.php:463
      PDOException::("SQLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails (`startup-reporter`.`category_news`, CONSTRAINT `category_news_news_id_foreign` FOREIGN KEY (`news_id`) REFERENCES `news` (`id`) ON DELETE CASCADE)")
  2   C:\laragon\www\startup-reporter\vendor\laravel\framework\src\Illuminate\Database\Connection.php:463
      PDOStatement::execute()

有什么想法为什么出错以及我需要做什么来修复它吗？

谢谢。

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2 答案

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问题的原因是在调用CategoryNewsTableSeeder文件之前，需要先调用NewsTableSeeder文件。解决方法是重新调整DatabaseSeeder.php文件的顺序。

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在使用工厂为外键生成数据时，出现了"使用工厂为外键生成数据时出现的错误"。这个错误的原因是，当尝试添加一个新的记录category_news，其中category_id=16，而数据库中没有id为16的category，因此约束会抛出一个错误。不能使用随机整数来分配给外键引用。解决方法是，在工厂函数中使用以下代码：

$factory->define(CategoryNews::class, function (Faker $faker) {
  return [
    'category_id' => Category::all()->random()->id,
    'news_id' => News::all()->random()->id,
  ];
});

我在这里找到了这种解决方法：https://stackoverflow.com/a/44102531/10573560

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