迁移：无法在 Laravel 6 中添加外键约束

Question

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

Illuminate\Database\QueryException : SQLSTATE[HY000]: General error: 1215 Cannot add foreign key constraint (SQL: alter table posts add constraint posts_category_id_foreign foreign key (category_id) references 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

将您的外键声明拆分为它们自己的架构方法...

我不明白问题的原因，但这样做对我来说一直有效。

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');
});

Answer 2

在您的 posts 架构中，您在删除时将 author_id 和 category_id 设置为空，但您没有将这些字段设置为可为空。将定义更改为：

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

应该这样做。

迁移：无法在 Laravel 6 中添加外键约束

Migration: Cannot add foreign key constraint in Laravel 6

php

mysql

laravel

laravel-6