Laravel：使用工厂作为外键时出错答案

【问题标题】：Laravel: Error When Using a Factory for a Foreign KeyLaravel：使用工厂作为外键时出错
【发布时间】：2020-03-31 10:46:20
【问题描述】：

我有以下迁移（对于数据透视表）：

        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');
        });

我想在该表中植入一些虚拟数据——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)
  ];

});

但是，当我运行以下命令时：php artisan migrate:fresh --seed，我收到以下错误：

 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()

知道为什么以及我需要做些什么来修复它吗？

谢谢。

【问题讨论】：

标签： laravel laravel-6

【解决方案1】：

我想通了——我必须重新排序我的DatabaseSeeder.php 文件才能调用NewsTableSeeder 文件在我调用CategoryNewsTableSeeder 文件之前。

【讨论】：

【解决方案2】：

您正在尝试添加新记录 category_news，其中 category_id=16 虽然您没有 id = 16 的类别，但约束将引发错误... 您不能使用 random int 将其分配给您的外键引用... 你可以简单地做这样的事情：

$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方式： https://stackoverflow.com/a/44102531/10573560

【讨论】：