Laravel 迁移无法添加外键

Question

我正在尝试编写 Laravel 数据库迁移，但收到以下关于外键的错误：

  [Illuminate\Database\QueryException]                                                                                                                                                                                                                    
  SQLSTATE[42000]: Syntax error or access violation: 1072 Key column 'category_id' doesn't exist in table (SQL: alter table `subcategories` add constraint subcategories_category_id_foreign foreign key (`category_id`) references `categories` (`id`))  



  [PDOException]                                                                                           
  SQLSTATE[42000]: Syntax error or access violation: 1072 Key column 'category_id' doesn't exist in table 

categories

和

subcategories

表确实已创建，但外键并未创建。这是我的迁移：

<?php

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

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

        Schema::create('subcategories', function ($table) {
            $table->increments('id')->unsigned();
            $table->foreign('category_id')->references('id')->on('categories');
            $table->string('name')->unique();
        });
    }

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

有什么想法吗？谢谢！

Answer 1

您应该在创建外键之前创建列：

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

---

文档：http://laravel.com/docs/5.1/migrations#foreign-key-constraints

Answer 2

Laravel 7、8

正如Limon Monte提到的，首先创建列，然后添加外键约束

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

Answer 3

整数对我不起作用。相反，我使用 bigInteger 来创建外键：

$table->bigInteger('category_id')->unsigned()->index()->nullable();
$table->foreign('category_id')->references('id')->on('categories')->onDelete('cascade');

Answer 4

我忘记将

->get()

添加到我调用的方法中。

Answer 5

只需使用

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