Question

进行迁移我收到此错误： SQLSTATE [HY000]：常规错误：1215无法添加外键约束（SQL：alter table books添加约束books_writer_id_foreign外键（writer_id）引用writers（{{1 }}））我尝试了很多东西，但没有人看起来工作。

2018_02_18_3165165_create_books_table.php

id

2018_02_18_192915_create_writers_table

<?php

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

class CreateBooksTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('books', function (Blueprint $table) {
            $table->engine = 'InnoDB';

            $table->increments('id');


            $table->string('name');
            $table->text('description');

            $table->integer('numPages');
            $table->enum('language', ['spanish', 'english']);

            $table->date('wrote_date')->nullable();


            $table->timestamp('created_at')->useCurrent();
            $table->timestamp('updated_at')->default(DB::raw('CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP'));
        });
        Schema::table('books', function (Blueprint $table) {
            $table->integer('writer_id')->unsigned();
            $table->foreign('writer_id')->references('id')->on('writers');
        });
    }

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

修改：错误是因为第一次迁移是书籍，然后是造成错误的作者。

Answer 1

有时根据我的经验，过于接近的时间戳会破坏代码并抛出异常，因为程序认为在books表尝试更改writers_table时间戳之后创建了writers表：
2018_02_16_31615

Answer 2

更改迁移源your_table_name

Schema::create('your_table_name', function (Blueprint $table) {
$table->BigIncrements('id');

到

Schema::create('your_table_name', function (Blueprint $table) {
$table->increments('id');

Answer 3

将其设为unsignedInteger，因为您正在使用increments()

$table->unsignedInteger('writer_id')->nullable();

Answer 4

将此行移至第一个闭包：

from urllib.request import urlopen, Request
from bs4 import BeautifulSoup as soup

my_url = "https://www.transfermarkt.com/wettbewerbe/europa/"
client = Request(my_url, headers={"User-Agent" : "Mozilla/5.0"})

page = urlopen(client).read()
print(page)

在以下之后立即：

$table->integer('writer_id')->unsigned();

此外，您需要为两个迁移文件添加时间戳，以便Laravel首先创建$table->timestamp('updated_at')->default(DB::raw('CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP'));表，然后创建writers表：

books

常规错误：1215无法在laravel中添加外键约束

4 个答案: