laravel - 如何修复在 Laravel 中迁移表时外键约束错误形成的错误

Question

迁移我的数据库时，出现此错误。下面是我的代码，后面是我在尝试运行迁移时遇到的错误。

代码

public function up()
{
    Schema::create('meals', function (Blueprint $table) {
        $table->increments('id');
        $table->integer('user_id')->unsigned();
        $table->integer('category_id')->unsigned();
        $table->string('title');
        $table->string('body');
        $table->string('meal_av');
        $table->timestamps();
        $table->foreign('user_id')
            ->references('id')
            ->on('users')
            ->onDelete('cascade');
        $table->foreign('category_id')
            ->references('id')
            ->on('categories')
            ->onDelete('cascade');
    });
}  

错误消息

[Illuminate\Database\QueryException]
SQLSTATE[HY000]: General error: 1005 Can't create tablemeal.#sql-11d2_1 4 (errno: 150 "Foreign key constraint isincorrectly formed") (SQL: alter
table meals add constraint meals_category_id_foreign foreign key (category_id) references categories (id) on deletecascade)

Answer 1

在 Laravel 中创建新表时。将生成如下迁移:

$table->bigIncrements('id');

而不是(在旧的 Laravel 版本中):

$table->increments('id');

当使用bigIncrements时，外键需要一个bigInteger而不是integer。所以你的代码将如下所示:

public function up()
    {
        Schema::create('meals', function (Blueprint $table) {
            $table->increments('id');
            $table->unsignedBigInteger('user_id'); //changed this line
            $table->unsignedBigInteger('category_id'); //changed this line
            $table->string('title');
            $table->string('body');
            $table->string('meal_av');
            $table->timestamps();

            $table->foreign('user_id')
                ->references('id')
                ->on('users')
                ->onDelete('cascade');

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

您还可以使用 increments 而不是 bigIncrements，如 Kiko Sejio说。

Integer 和 BigInteger 之间的区别在于大小:

• int => 32 位
• bigint => 64 位