> For the complete documentation index, see [llms.txt](https://liseen315.gitbook.io/laravel/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://liseen315.gitbook.io/laravel/shu-ju-ku-he-eloquent/pei-zhi/ding-yi-qian-yi.md).

# 定义迁移

迁移是一个单独的文件,它定义了两件事:运行up迁移执行的修改,以及运行down迁移执行的修改.

> 迁移中的"up"和"down"
>
> 迁移总是按照时期运行,每个迁移文件的名字都类似这样:2014\_10\_12\_000000\_create\_users\_table.php，当一个新系统被迁移时,系统会抓取每个迁移,并运行它们的up方法-此时你正在”向上“执行迁移,迁移系统还允许你执行"回滚"最近的一组迁移,它将运行down方法,该方法将撤销up迁移所在的更改.
>
> 所以迁移的up应该叫执行迁移,down叫撤销迁移.

示例5-2显示了Laravel自带的"create users table"迁移.

{% code title="Example 5-2. Laravel’s default “create users table” migration" %}

```php
<?php

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

class CreateUsersTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('users', function (Blueprint $table) {
            $table->bigIncrements('id');
            $table->string('name');
            $table->string('email')->unique();
            $table->timestamp('email_verified_at')->nullable();
            $table->string('password');
            $table->rememberToken();
            $table->timestamps();
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::dropIfExists('users');
    }
}

```

{% endcode %}

{% hint style="info" %}
邮箱验证

email\_verified\_at字段只出现在Laravel 5.7及之后的版本,它存储了用户验证邮箱地址的时间戳
{% endhint %}

现在我们有一个up方法告诉迁移帮我们创建一个名叫users的新表格,它带有一些字段,down方法告诉迁移丢弃users表格


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://liseen315.gitbook.io/laravel/shu-ju-ku-he-eloquent/pei-zhi/ding-yi-qian-yi.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.