Question

我的数据库中有2个表。

books和ratings

在books中 id，name

在ratings

中

id，book_id，rating

我为这些模型设置了很多关系。

在Book模型中-

public function ratings()
{
    return $this->hasMany('App\Rating');
}

在Rating模型中-

public function book()
{
    return $this->belongsTo('App\Book');
}

现在，我想获取所有具有平均评分但按高评分排序的图书。

所以我首先评价高的书，然后评价低的书。

所以我如何联接2个表以实现此结果。

谢谢。

Answer 1

您可以使用修改后的withCount()：

$books = Book::withCount(['ratings as average_rating' => function($query) {
    $query->select(DB::raw('coalesce(avg(rating),0)'));
}])->orderByDesc('average_rating')->get();

Answer 2

该查询看起来像这样：

SELECT book.id, AVG(ratings.rating) AS avg_rating 
FROM ratings
JOIN book ON book.id = ratings.book_id
/* WHERE AVG(ratings.rating) > 4 You could say only return results where rating > 4 */
GROUP BY book.id
ORDER BY AVG(ratings.rating) DESC LIMIT 5;

您需要将两个表连接起来，在书上使用带有group by的聚合函数。然后只需排序并限制结果即可。

更新：

针对您的问题：

SELECT book.id, COALESCE(AVG(ratings.rating), 0) AS avg_rating 
FROM book
*LEFT* JOIN ratings ON book.id = ratings.book_id    
GROUP BY book.id
ORDER BY AVG(ratings.rating);

使用view可能会在简化ORM和查询的合理性之间做出折衷。

Answer 3

通过Collections *

    $books = Book::with('ratings')
        ->get()
        ->sortBy(function($bk, $key) {
            if($bk->rating) {
                return $bk->rating->rating;
            }
            return null;
        });

通过加入

  $books = Book::join('rating', 'rating.book_id', '=', 'book.id')
                 ->orderBy('ratings.rating', 'desc')
                 ->select('books.*')
                 ->get();

Answer 4

Books::withAvg('ratings', 'rating')->orderBy('ratings_avg_rating', 'desc')->take(5)->get();

这适用于 Laravel 8

如何通过Laravel 5中的Desc获得平均

4 个答案: