Question

我正在尝试使用对象中包含的值的总和来设置数组。但是，当在对象中未设置其中一个属性（此示例中为“shares”）时，操作应该继续而不会引发以下错误：

“[ErrorException] Undefined property：stdClass :: $ shares”

我正在尝试使用三元运算符来实现此目的，如下所示：

$array = [strtotime('today midnight') =>
           $ExternalPost->reactions->summary->total_count ?: 0 +
           $ExternalPost->comments->summary->total_count ?: 0 +
           ($ExternalPost->shares->count ? $ExternalPost->shares->count : 0)
         ];

看起来运算符正在评估所有内容，包括其他两个前面的对象/值。如何将评估值限制为最后一个“$ ExternalPost-＆gt; shares-＆gt; count”？

Answer 1

我建议重写你的逻辑，这样它就不会同时使用多个三元运算符。 PHP comparison operators documentation说：

注意：

建议您避免＆＃34;堆叠＆＃34;三元表达式。在单个语句中使用多个三元运算符时，PHP的行为是不明显的：

示例＃4非明显的三元行为

<?php // on first glance, the following appears to output 'true' echo (true?'true':false?'t':'f'); // however, the actual output of the above is 't' // this is because ternary expressions are evaluated from left to right // the following is a more obvious version of the same code as above echo ((true ? 'true' : false) ? 't' : 'f'); // here, you can see that the first expression is evaluated to 'true', which // in turn evaluates to (bool)true, thus returning the true branch of the // second ternary expression. ?>

这是因为PHP的三元运算符是左关联的而不是右关联的，就像在大多数其他语言中一样。

Answer 2

如果未定义$ExternalPost->shares，则没有理由在没有该错误的情况下继续操作。如果您正在检查$ExternalPost->shares->count

，则需要定义此选项

否则，您可以将逻辑更改为：

((isset($ExternalPost->shares) && $ExternalPost->shares->count) ? $ExternalPost->shares->count : 0)

Answer 3

如果您尝试访问不存在的对象属性或数组键，PHP将抛出错误，即使您只是这样做以检查它是否存在。相反，您应该使用property_exists()（对于对象），或array_key_exists()（对于数组）或isset()（对于任何事物）。使用其中一种方法可以检查变量/属性/键是否存在而不会抛出错误，如果它没有。

您的示例可以重写为：

...
(isset($ExternalPost->shares->count) ? $ExternalPost->shares->count : 0)

Answer 4

您的原始代码相当于

if ($ExternalPost->reactions->summary->total_count) {
    $a = $ExternalPost->reactions->summary->total_count;
} else {
    if ($ExternalPost->comments->summary->total_count) {
      $a = 0 + $ExternalPost->comments->summary->total_count;
    } elseif($ExternalPost->shares->count) {
      $a = 0 + $ExternalPost->shares->count
    } else {
      $a = 0;
    }
}

示例http://ideone.com/c9bY5o

三元条件应包含括号和属性验证，以区分现有值和检索值。

(isset($ExternalPost->reactions->summary->total_count) ? $ExternalPost->reactions->summary->total_count : 0) +
(isset($ExternalPost->comments->summary->total_count) ? $ExternalPost->comments->summary->total_count : 0) +
(isset($ExternalPost->shares->count) ? $ExternalPost->shares->count : 0);

否则使用详细格式，这更容易阅读。

if (isset($ExternalPost->reactions->summary->total_count)) {
    $a = $ExternalPost->reactions->summary->total_count;
} else {
    $a = 0;
}
if (isset($ExternalPost->comments->summary->total_count)) {
    $a += $ExternalPost->comments->summary->total_count;
} else {
    $a += 0;
}
if (isset($ExternalPost->shares->count)) {
    $a += $ExternalPost->shares->count;
} else {
    $a += 0;
}

示例http://ideone.com/GKkpZw

请注意，该对象已移除reactions和shares个属性。

至于建议，我建议您将方法分配给对象并以此方式获取总计。因此，您只需要在一个位置维护计算，并且能够在其他脚本中重复使用它。

这样，如果你想对数据做一些更复杂的事情，需要在别处显示它，或者你决定稍后更改或添加对象或计算，它会更容易。例如，只有当帖子有份额或添加向上和向下投票时，总计反应和评论。

Rough Lazy Getter OOP示例 - 它可以重构为在设置值时计算总数，接受一组值等等。

class ExternalPost
{
    private $reactions;

    private $comments;

    private $shares;

    public function __construct(Reactions $reactions = null, Comments $comments = null, Shares $shares = null) 
    {
        $this->reactions = $reactions;
        $this->comments = $comments;
        $this->shares = $shares;
    }

    public function getReactions()
    {
        if (null === $this->reactions) {
            $this->reactions = new Reactions;
        }
        return $this->reactions;
    }

    public function getComments()
    {
        if (null === $this->comments) {
            $this->comments = new Comments;
        }
        return $this->comments;
    }

    public function getShares()
    {
        if (null === $this->shares) {
            $this->shares = new Shares;
        }
        return $this->shares;
    }

    public function getTotal() 
    {
        return $this->getReactions()->getTotal() + 
            $this->getComments()->getTotal() + 
            $this->getShares()->getCount();
    }
}

class Summary 
{
    private $total_count = 0;

    public function getTotalCount() 
    {
        return $this->total_count;
    }

    public function setTotalCount($total)
    {
        $this->total_count = $total;

        return $this;
    }
}

abstract class Summation 
{
    protected $summary;

    public function __construct(Summary $summary = null) 
    {
        $this->summary = $summary;
    }

    public function getSummary()
    {
        if (null === $this->summary) {
            $this->summary = new Summary;
        }

        return $this->summary;
    }

    public function getTotal() 
    {
        return $this->getSummary()->getTotalCount();
    }

    public function setTotal($total)
    {
        $this->getSummary()->setTotalCount($total);

        return $this;
    }
}

class Reactions extends Summation{}

class Comments extends Summation{}

class Shares 
{
    private $count = 0;

    public function getCount() 
    {
        return $this->count;
    }

    public function setCount($count)
    {
        $this->count = $count;

        return $this;
    }
}

所以现在脚本中的代码看起来像

$reactions = new Reactions;
$reactions->setTotal(1);
$comments = null; 
/*
 $comments = new Comments;
 $comments->setTotal(2);
 //alternative to using getComments below
*/

$ExternalPost = new ExternalPost($reactions, $comments);
/* $ExternalPost->getReactions()->setTotal(1);
   //alternative to defining $reactions above */
$ExternalPost->getComments()->getSummary()->setTotalCount(2);
$ExternalPost->getShares()->setCount(3);

$array = [strtotime('today midnight') => $ExternalPost->getTotal()];

示例http://ideone.com/oqSYNd

您还可以应用__set和__get魔术方法来保留您当前的代码格式，但我们强烈建议不要这样做，因为它会让您的代码更容易理解。

三元运算符里面计算PHP

4 个答案: