laravel 8 (errno: 150“外键约束不正确”)

Question

我试着在最后一个php和laravel 8中创建论坛。我在udemy购买了laravel 8的课程，我跟随他的视频，但在我的电脑中有错误，在视频中没有。

2021_11_13_000535_create_posts_table

use Illuminate\Database\Migrations\Migration;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Support\Facades\Schema;

class CreatePostsTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('posts', function (Blueprint $table) {
            $table->id();
            $table->string('title');
            $table->integer('is_deleted');
            $table->integer('is_approved');
            $table->string('image');
            $table->unsignedBigInteger('discussion_id');
            $table->foreign('discussion_id')->references('id')->on('discussions')->onDelete('cascade');
            $table->unsignedBigInteger('user_id');
            $table->foreign('user_id')->references('id')->on('users')->onDelete('cascade');
            $table->string('slug');
            $table->timestamps();
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::dropIfExists('posts');
    }
}

2021_11_19_165302_create_discussions_table

<?php

use Illuminate\Database\Migrations\Migration;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Support\Facades\Schema;

class CreateDiscussionsTable extends Migration
{
   /**
    * Run the migrations.
    *
    * @return void
    */
   public function up()
   {
       Schema::create('discussions', function (Blueprint $table) {
           $table->id();
           $table->string('title');
           $table->string('desc');
           $table->unsignedBigInteger('forum_id');
           $table->foreign('forum_id')->references('id')->on('forums')->onDelete('cascade');
           $table->integer('is_deleted')->default(0);
           $table->string('image')->nullable();
           $table->integer('notify')->default(0);
           $table->unsignedBigInteger('user_id');
           $table->foreign('user_id')->references('id')->on('users')->onDelete('cascade');

           $table->timestamps();
       });
   }

   /**
    * Reverse the migrations.
    *
    * @return void
    */
   public function down()
   {
       Schema::dropIfExists('discussions');
   }
}

当我尝试迁移表时，我有以下错误：

Migrated:  2014_10_12_000000_create_users_table (1,399.45ms)
Migrating: 2014_10_12_100000_create_password_resets_table
Migrated:  2014_10_12_100000_create_password_resets_table (2,117.91ms)
Migrating: 2019_08_19_000000_create_failed_jobs_table
Migrated:  2019_08_19_000000_create_failed_jobs_table (1,592.76ms)
Migrating: 2019_12_14_000001_create_personal_access_tokens_table
Migrated:  2019_12_14_000001_create_personal_access_tokens_table (2,125.96ms)
Migrating: 2021_11_12_234608_create_categories_table
Migrated:  2021_11_12_234608_create_categories_table (2,452.77ms)
Migrating: 2021_11_12_235039_create_forums_table
Migrated:  2021_11_12_235039_create_forums_table (2,849.71ms)
Migrating: 2021_11_13_000340_create_tags_table
Migrated:  2021_11_13_000340_create_tags_table (526.62ms)
Migrating: 2021_11_13_000535_create_posts_table

   Illuminate\Database\QueryException 

  SQLSTATE[HY000]: General error: 1005 Can't create table `stsdb`.`posts` (errno: 150 "Foreign key constraint is incorrectly formed") (SQL: alter table `posts` add constraint `posts_discussion_id_foreign` foreign key (`discussion_id`) references `discussions` (`id`) on delete cascade)

  at vendor/laravel/framework/src/Illuminate/Database/Connection.php:703
    699▕         // If an exception occurs when attempting to run a query, we'll format the error
    700▕         // message to include the bindings with SQL, which will make this exception a
    701▕         // lot more helpful to the developer instead of just the database's errors.
    702▕         catch (Exception $e) {
  ➜ 703▕             throw new QueryException(
    704▕                 $query, $this->prepareBindings($bindings), $e
    705▕             );
    706▕         }
    707▕     }

      +9 vendor frames 
  10  database/migrations/2021_11_13_000535_create_posts_table.php:28
      Illuminate\Support\Facades\Facade::__callStatic()

      +21 vendor frames 
  32  artisan:37
      Illuminate\Foundation\Console\Kernel::handle()

有人可以解释为什么会有这个错误，以及如何解决这个问题？因为我不明白，我跟在我的个人电脑的视频中有错误，而在视频中没有。有人能帮我解决这个问题吗？我已经在谷歌上注册了，但是我没有找到解决这个问题的方法，我用电报通知了tuts构建论坛laravel 8。

Answer 1

问题是，对于posts表的迁移是在讨论迁移之前运行的。

这是因为Laravel运行迁移文件名中的时间戳命令的迁移：

2021_11_13_000535_create_posts_table -> 13. November
2021_11_19_165302_create_discussions_table -> 19. November

因此，还没有像我的评论所建议的那样创建dicsussions表！

解决方案很简单，请将文件名更改为：

2021_11_20_000535_create_posts_table -> 20. November

下一次，请按照我前面的建议查看一下您的DB。

来自他们的文档：

生成移动

您可以使用make:migration命令来生成数据库迁移。新的迁移将放在数据库/迁移目录中。每个迁移文件名都包含一个时间戳，允许Laravel确定迁移的顺序：

https://laravel.com/docs/8.x/migrations#generating-migrations