Laravel 迁移将外键更改为 nullOnDelete() 和 nullable(true)答案

【问题标题】：Laravel migrations change foreign key to be nullOnDelete() and nullable(true)Laravel 迁移将外键更改为 nullOnDelete() 和 nullable(true)
【发布时间】：2023-02-06 03:34:58
【问题描述】：

我有这个迁移，我第一次创建了一个外键：

        Schema::table('user_plays_quizzes', function (Blueprint $table) {
            $table->bigInteger('quiz_id')->unsigned()->change();
            $table->foreign('quiz_id')->references('id')->on('quizzes');
        });

现在我有一个新的迁移，我想将这个外键更新为nullable(true)和nullOnDelete()。

试了很多次，总是报错，感觉最接近的做法是：

        Schema::table('user_plays_quizzes', function (Blueprint $table) {
            $table->bigInteger('quiz_id')->unsigned()->nullable(true)->change();
            $table->foreign('quiz_id')->references('id')->on('quizzes')->nullOnDelete();
        });

可悲的是它也不起作用：

SQLSTATE[HY000]: General error: 1005 Can't create table `d039e62e`.`user_plays_quizzes` (errno: 121 
"Duplicate key on write or update") (SQL: alter table `user_plays_quizzes` add constraint `user_plays_quizzes_quiz_id_foreign` for
eign key (`quiz_id`) references `quizzes` (`id`) on delete set null)

不知道如何解决它。我什至不能放下钥匙并重新创建它们。也许有人知道我如何通过迁移更新它

【问题讨论】：

标签： laravel migration

【解决方案1】：

为什么不能删除密钥并重新创建它？

public function up()
{
    Schema::table('user_plays_quizzes', function (Blueprint $table) {
        // Drop fk constraint on quiz_id column
        $table->dropForeign(['quiz_id']);
        // Alter quiz_id column
        $table->bigInteger('quiz_id')->unsigned()->nullable(true)->change();
        // Add new fk constraint on quiz_id column
        $table->foreign('quiz_id')->references('id')->on('quizzes')->nullOnDelete();

    });
}

public function down()
{
    Schema::table('user_plays_quizzes', function (Blueprint $table) {
        // Drop fk constraint on quiz_id column
        $table->dropForeign(['quiz_id']);
        // Restore quiz_id column to how it was before
        $table->bigInteger('quiz_id')->unsigned()->nullable(false)->change();
        // Restore original fk constraint on quiz_id column
        $table->foreign('quiz_id')->references('id')->on('quizzes');
    });
}

【讨论】：