Illuminate\Database\QueryException SQLSTATEHY000：一般错误：1215

Question

我目前正在做一个学校项目，我的数据库遇到了这个问题， 我想与视频和类别建立关系，这是我的两个表。 视频表：

<?php

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

class CreateVideosTable extends Migration
{
/**
 * Run the migrations.
 *
 * @return void
 */
public function up()
{
    Schema::create('videos', function (Blueprint $table) {
        $table->increments('id');
        $table->string('name')->default('');
        $table->string('url')->default('');

        $table->integer('category_id')->unsigned()->nullable();
        $table->foreign('category_id')->references('id')->on('categories');

        $table->string('img_url')->default('');
        $table->integer('views')->nullable();
        $table->integer('rating')->nullable();
        $table->timestamps();
    });
}

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

还有分类表：

<?php

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

class CreateCategoriesTable extends Migration
{
/**
 * Run the migrations.
 *
 * @return void
 */
public function up()
{
    Schema::create('categories', function (Blueprint $table) {
        $table->increments('id');
        $table->string('name');
        $table->timestamps();
    });
}

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

当我在控制台中运行 php artisan migrate:refresh 我得到这个错误：

[Illuminate\Database\QueryException] SQLSTATE[HY000]: General error: 1215 
Cannot add foreign key constraint (SQL: alter table `videos` add constraint 
`videos_category_id_foreign` foreign key (`category_id`) references 
`categories` (`id`))

[PDO异常] SQLSTATE[HY000]: 一般错误：1215 无法添加外键约束

我不明白为什么，因为当我改变这个时：

$table->foreign('category_id')->references('id')->on('categories');

到这里：

$table->foreign('category_id')->references('id')->on('users');

它有效，然后我没有任何错误，我希望有人能帮助我解决这个问题！

Answer 1

您应该在视频表之前创建您的类别表

您可以使用它并删除您的类别迁移：

<?php

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

class CreateVideosTable extends Migration
{
/**
 * Run the migrations.
 *
 * @return void
 */
public function up()
{
      // create categories table
  Schema::create('categories', function (Blueprint $table) {
    $table->increments('id');
    $table->string('name');
    $table->timestamps();
  });

     //now  create videos table
    Schema::create('videos', function (Blueprint $table) {
        $table->increments('id');
        $table->string('name')->default('');
        $table->string('url')->default('');

        $table->integer('category_id')->unsigned()->nullable();
        $table->foreign('category_id')->references('id')->on('categories');

        $table->string('img_url')->default('');
        $table->integer('views')->nullable();
        $table->integer('rating')->nullable();
        $table->timestamps();
    });
}

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