Question

我正在尝试在第一行years表（字段：colom_year）中获取所有值，并将字段year_start放在researches表中。所以我用这个：

use App/Research;
use App/Year;

public function updateDatabaseYearStartResearch()
{
    $researchs = Research::all();
    foreach($researchs as $r)
    {
            $yearNew = Year::where('research_id', $r->id) != null ? Year::where('research_id', $r->id)->first()->colom_year : 0;
            //dd($yearNew);
            $Riset = Research::find($r->id);
            $Riset->year_start =  $yearNew ;
            $Riset->save();
    }
}

当我dd($yearNew)获得价值时，我想我会使用真正的查询。但是，当我评论dd($yearNew)以运行我的函数时，会出现如下错误：

试图获取非对象的属性“ colom_year”

我认为这是错误的，因为null表中有years值，因此我使用此查询来处理错误： $yearNew = Year::where('research_id', $r->id) != null ? Year::where('research_id', $r->id)->first()->colom_year : 0;

但是我得到同样的错误。如何解决该错误？

Answer 1

<?php 

$year = Year::where('research_id', $r->id)->first();

$yearNew = $year ? $year->colom_year ?? 0 : 0;

以上将检查$ year是否包含一个值，如果其空值，则分配0
如果$year是具有数据的Year的有效实例，但不包含列colom_year，则再次分配0

Answer 2

Year::where('research_id', $r->id)是Builder的实例，不是查询本身的结果，因此它不会为null。您想做的是：

$years = Year::where('research_id', $r->id)->get();
$yearNew = $years->isEmpty() ? 0 : $years->first()->colom_year;

Answer 3

相反，您应该使用instanceof来检查Year是否为有效对象：

use App/Research;
use App/Year;

public function updateDatabaseYearStartResearch()
{
    $researchs = Research::all();
    foreach ($researchs as $r)
    {
        $yearNew = 0;
        $yearModel = Year::where('research_id', $r->id)->first();
        if($yearModel instanceof Year && isset($yearModel->colom_year)){
            $yearNew = $yearModel->colom_year;
        }
        //dd($yearNew);
        $Riset = Research::find($r->id);
        $Riset->year_start = $yearNew;
        $Riset->save();
    }
}

循环函数中的处理程序空值（Foreach）Laravel

3 个答案: