如何将 mysql 8 中的约束 FOREIGN KEY 从 laravel 迁移或原始 ZAC5C74B64B4B8352EF2F181AFFB5AC 中的“ON DELETE CASCADE”更改为“ON DELETE SET NULL”

Question

首先，我的英语很差。 对于那个很抱歉。

我在cards表中有一个外键，例如：

$table->foreignId('wallet_id')->constrained('wallets', 'id')->onDelete('cascade');

由于某些原因，我需要更改cascade以在该列上set null

我尝试过（在新的迁移中）：

$table->dropForeign('cards_wallet_id_foreign');
$table->foreignId('wallet_id')
    ->nullable()
    ->onDelete('set null')
    ->change();

运行正常，但删除时未设置 null:((

我该如何解决。 谢谢！！

Answer 1

您必须在新迁移中更改表迁移架构，并确保将外键字段设置为可为空：

$table->integer('wallet_id')->unsigned()->nullable();

然后像这样使用set null ：

$table->...->onDelete('set null');

Answer 2

如果要首先更改FOREIGN KEY约束，则需要删除外键的先前索引并仅将外键约束重新添加到列。

尝试这个：

Schema::table('cards', function (Blueprint $table) {
            //Drop Previous Index
            $table->dropForeign('cards_wallet_id_foreign');

            //Since we want to set null on Delete Or Update
            $table->unsignedBigInteger('wallet_id')->nullable()->change();

            //Adding Only Forign key Constraints to column
            //calling foreignId will re attempt to create a column
            $table->foreign('wallet_id')->references('id')->on('wallets')->onDelete('set null')->onUpdate('set null')->change();

        });

Answer 3

你不能只修改现有的迁移，你需要再做一个

<?php
  
use Illuminate\Support\Facades\Schema;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;
  
class ChangeSomeTableColumn extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::table('the_table_you_are_changing', function (Blueprint $table) {
            $table
                ->foreignId('wallet_id')
                ->constrained('wallets', 'id')
                ->onDelete('set null')
                ->change();
        });
    }
    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
          
    }
}

Answer 4

经过多次收集和尝试，我找到了最好的解决方案（不需要drop column）

<?php

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

class AlterWalletIdColumnInCardsTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::table('cards', function (Blueprint $table) {
            $table->dropForeign('cards_wallet_id_foreign');
            $table->foreignId('wallet_id')
                ->nullable()
                ->change();

            $table->foreign('wallet_id')
                ->on('wallets')
                ->references('id')
                ->onDelete('set null');
        });
    }

    /**
     * I recommend you don't use down (laravel 9 will remove it as default 
     * migration)
     */
    public function down()
    {
        Schema::table('cards', function (Blueprint $table) {
            $table->dropForeign('cards_wallet_id_foreign');
            $table->foreignId('wallet_id')
                ->nullable(false)
                ->change();

            $table->foreign('wallet_id')
                ->on('wallets')
                ->references('id')
                ->onDelete('cascade');
        });
    }
}