首先使用查询构建器 [英] Pluck together with first using Query builder

问题描述

如果我想使用 eloquent 获取数据库中第一个用户的姓名，我可以这样做:

If I want to get get name of first user in database using eloquent I can do something like that:

$user =  User::select('name')->first()->pluck('name');
// or $user =  User::first()->pluck('name');

echo $user;

仅以字符串形式获取此用户的名称.

to get only name of this user as string.

但是，如果我仅使用查询构建器尝试相同的操作:

However If I try the same using only query builder:

$user =  DB::table('users')->select('name')->first()->pluck('name');

echo $user;

我得到异常:

调用未定义的方法 stdClass::pluck()

Call to undefined method stdClass::pluck()

但不先使用它会起作用:

But without using first it will work:

$user =  DB::table('users')->select('name')->where('id',1)->pluck('name');

echo $user;

使用查询构建器无法将 pluck 与 first 一起使用，还是我做错了什么?

Is it not possible to use pluck with first using query builder or am I doing something wrong?

附注.当然我知道我可以使用 $user->name 显示任何属性而不使用 pluck 但我只是好奇为什么使用 Eloquent 它可以工作并使用 Query Builder 它仅在没有 first 和 pluck

PS. Of course I know that I can display any property using $user->name without using pluck but I'm just curious why using Eloquent it works and using Query Builder it works only when not having both first and pluck

推荐答案

你不想将 pluck 与 first 一起使用，因为它是多余的:

You don't want to use pluck with first, because it's redundant:

$query->first() // fetch first row
      ->pluck('name'); // fetch first row again and return only name

所以只使用pluck:

$query->pluck('name');

它可以满足您的所有需求.

It does all you need.

但还有更多.

在幕后 first 和 pluck 运行 2 个单独的查询，因此:

Under the hood first and pluck run 2 separate queries, so:

$query->where(..)->orderBy(..)->first() // apply where and orderBy
        ->pluck('name'); // no where and orderBy applied here!

所以在pluck之前使用first不仅是多余的，而且会导致意想不到的结果.

So it's not only redundant to use first before pluck, but also it causes unexpected results.

你可以在 Eloquent 查询上链接这些方法，因为它返回一个集合(get)或模型(first)，但是 QueryBuilder 只返回一个数组 (get) 或 stdObject (first).这就是为什么你不能在查询构建器上做同样的事情.

You can chain those methods on Eloquent query, since it returns a collection (get) or model (first), but QueryBuilder returns just an array (get) or stdObject (first). That's why you couldn't do the same oon the query builder.

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