Laravel 迁移外键问题

Question

我已经使用类别迁移创建了类别表，然后我尝试使用另一个迁移创建产品表，其中产品表中的外键 categories_id 到产品表中的 id。

请在下面找到我的迁移。

Categories migration

<?php

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('category_name', 255);
            $table->string('category_description', 255);

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

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

}

Products migration

<?php

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

class CreateProductsTable extends Migration {

    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('products', function(Blueprint $table)
        {
            $table->increments('id');
            $table->integer('category_id')->unsigned();
            $table->foreign('category_id')->reference('id')->on('categories');
            $table->string('product_name');
            $table->text('product_description');
            $table->decimal('product_cost', 10, 2);
            $table->text('product_image');
            $table->boolean('product_availability')->default(1);

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

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

}

当我在命令行中运行 php artisan migrate 命令时出现以下错误

[Illuminate\Database\QueryException]
SQLSTATE[42000]: Syntax error or access violation: 1064 You have an error i
n your SQL syntax; check the manual that corresponds to your MySQL server v
ersion for the right syntax to use near ')' at line 1 (SQL: alter table `pr
oducts` add constraint products_category_id_foreign foreign key (`category_
id`) references `categories` ())

Answer 1

你可以试试这个（注意unsigned和references你用过reference）：

// unsigned() should be used during declaration
$table->integer('category_id')->unsigned();

// reference() should be references()
$table->foreign('category_id')->references('id')->on('categories');

更新：

首先创建products 表，然后添加foreign 键。创建表时删除以下行：

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

然后使用这个添加外键：

Schema::table('products', function($table) {
    $table->foreign('category_id')->references('id')->on('categories');
});

两者应该是不同的：

Schema::create('products', function(Blueprint $table)
{
    $table->increments('id');
    $table->integer('category_id')->unsigned();
    $table->string('product_name');
    // more ...
});

Schema::table('products', function($table) {
    $table->foreign('category_id')->references('id')->on('categories');
});

Answer 2

unsigned() 应该在设置类型时定义，而不是在设置外键时。另外，reference() 应该是 references()

相应的行应该这样改：

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