Question

我正在尝试在Laravel中创建外键。但是，当我使用Artisan迁移表时，出现以下错误。

Illuminate \ Database \ QueryException：SQLSTATE [HY000]：常规错误： 1215无法添加外键约束（SQL：alter table posts add 约束posts_category_id_foreign外键（category_id）引用categories（id））

帖子迁移

Schema::create('posts', function (Blueprint $table) {
    $table->uuid('id')->primary();
    $table->string('title');
    $table->string('slug')->unique();
    $table->longText('content');
    $table->string('image')->nullable();
    $table->uuid('author_id');
    $table->uuid('category_id');
    $table->timestamps();
    $table->foreign('author_id')->references('id')->on('users')->onDelete('set null');
    $table->foreign('category_id')->references('id')->on('categories')->onDelete('set null');
});

类别迁移

Schema::create('categories', function (Blueprint $table) {
    $table->uuid('id')->primary();
    $table->string('name');
    $table->string('slug')->unique();
    $table->uuid('parent')->nullable();
});

Answer 1

在您的posts模式中，您将删除时将author_id和category_id设置为空，但是没有将这些字段设置为可空。将定义更改为：

$table->uuid('author_id')->nullable();
$table->uuid('category_id')->nullable();

应该这样做。

Answer 2

将外键声明拆分为自己的Schema方法...

我不了解问题的原因，但是这样做一直对我有用。

Schema::create('posts', function (Blueprint $table) {
    $table->uuid('id')->primary();
    $table->string('title');
    $table->string('slug')->unique();
    $table->longText('content');
    $table->string('image')->nullable();
    $table->uuid('author_id');
    $table->uuid('category_id');
    $table->timestamps();
});

Schema::table('posts', function(Blueprint $table) {
    $table->foreign('author_id')->references('id')->on('users')->onDelete('set null');
    $table->foreign('category_id')->references('id')->on('categories')->onDelete('set null');
});

迁移：无法在Laravel 6中添加外键约束

2 个答案: