如何使該循環更快？

Question

我正在將Laravel 5.2用於我正在從事的項目。 關於我如何利用Laravel來使此循環更快地運行，是否有人有任何提示？

foreach ($purchaseYears as $purchaseYear){

$totalInventory = \App\Inventory::where('purchase_year', $purchaseYear)->count();

if ($purchaseYear < 1960) { $purchaseYear = 'Pre 1960'; }
else if ($purchaseYear >= 1960 && $purchaseYear < 1965) { $purchaseYear = '1960-64'; }
else if ($purchaseYear >= 1965 && $purchaseYear < 1970) { $purchaseYear = '1965-69'; }
else if ($purchaseYear >= 1970 && $purchaseYear < 1975) { $purchaseYear = '1970-74'; }
else if ($purchaseYear >= 1975 && $purchaseYear < 1980) { $purchaseYear = '1975-79'; }
else if ($purchaseYear >= 1980 && $purchaseYear < 1985) { $purchaseYear = '1980-84'; }
else if ($purchaseYear >= 1985 && $purchaseYear < 1990) { $purchaseYear = '1985-89'; }
else if ($purchaseYear >= 1990 && $purchaseYear < 1995) { $purchaseYear = '1990-94'; }
else if ($purchaseYear >= 1995 && $purchaseYear < 2000) { $purchaseYear = '1995-99'; }
else if ($purchaseYear >= 2000 && $purchaseYear < 2005) { $purchaseYear = '2000-04'; }
else if ($purchaseYear >= 2005 && $purchaseYear < 2010) { $purchaseYear = '2005-09'; }
else if ($purchaseYear >= 2010 && $purchaseYear < 2015) { $purchaseYear = '2010-14'; }
else if ($purchaseYear >= 2015 && $purchaseYear < 2019) { $purchaseYear = '2015-19'; }

if (isset($chartData[$purchaseYear])) {
    $prev = $chartData[$purchaseYear];
    $chartData[$purchaseYear] = $totalInventory + $prev;
    $prev = null;
} else {
    $chartData[$purchaseYear] = $totalInventory;
}

}

Answer 1

我認為您可以將日期分解為一個模式，而不僅僅是每隔十年進行測試，如下所示：

if ($purchaseYear < 1960) { 
   $purchaseYear = 'Pre 1960'; 
} else {
   $prefix = substr($purchaseYear,0,2);
   $decade = substr($purchaseYear,1,1);
   $suffix = substr($purchaseYear,-1);
   $purchYear = $prefix . $decade 
   if ($suffix<5) {
      $purchYear .= '0-' . $decade . '4'; 
   } else {
      $purchYear .= '5-' . $decade . '9'
}

還沒有測試過，但是我認為它會做您想要的。

Answer 2

我認為最耗時的部分應該是執行查詢。 如果使用whereIn ，那么我認為您只能執行一次查詢，然后遍歷結果。 我沒有測試過，但是應該是這樣的：

$purchasesByYear = \App\Inventory::select('purchase_year',
    DB::raw('count(*) as purchase_count'))
        ->whereIn('purchase_year', $purchaseYears)
        ->groupBy('purchase_year')->get();

我認為減少查詢執行次數將是防止其緩慢運行的主要機會。 另外，如果您尚未將索引添加到purchase_year，我認為它會有所幫助。

您可以使用一些數學運算來代替對年份進行分組的其他條件。 這實際上可能會稍慢一些，但是代碼的重復性會降低一些，而且我相信與查詢部分相比，您對該部分所做的任何事情都將是微優化。 我的建議：

foreach ($purchasesByYear as $purchaseYear) {
    $year = $purchaseYear->purchase_year;
    if ($year < 1960) {
        $yearRange = 'Pre 1960';
    } else {
        // subtract one until the year is a multiple of five
        while ($year % 5) { $year--; }
        // then construct the range string using the starting number
        $yearRange = $year.'-'.($year+4);
    }
    if (isset($chartData[$yearRange])) {
        $chartData[$yearRange] += $purchaseYear->purchase_count;
    } else {
        $chartData[$yearRange] = $purchaseYear->purchase_count;
    }
}