Propel2與表連接，然后按聚合函數分組

Question

我有兩個表：food（id，name），review（user_id，food_id，rating）。 現在我想將食物表與評論表連接起來，並在虛擬食物表中添加名稱為avg_rating的虛擬列，該虛擬列顯然將保留基於評論的食物的平均評分值。 所以我的想法是做這樣的事情：

$food = FoodQuery::create()
        ->filterById(15) // constant for testing purposes only
        ->leftJoinWithReview()
        ->withColumn("AVG(review.rating)", "avg_rating")
        ->groupBy("review.rating")
        ->find()

現在在調試器中，我看到以下內容：

result = {Propel\Runtime\Collection\ObjectCollection} [7]
 index = {array} [1]
 indexSplHash = {array} [1]
 model = "Food"
 fullyQualifiedModel = \Food
 formatter = {Propel\Runtime\Formatter\ObjectFormatter} [10]
 data = {array} [1]
  0 = {\Food} [34]
   new = false
   deleted = false
   modifiedColumns = {array} [0]
   virtualColumns = {array} [1]
    avg_rating = "5.0000"
   id = 15
   name = "Salát Caesar"
   collReviews = {Propel\Runtime\Collection\ObjectCollection} [7]
    index = {array} [2]
    indexSplHash = {array} [2]
    model = "Review"
    fullyQualifiedModel = "\Review"
    formatter = null
    data = {array} [2]
     0 = {\Review} [14]
      new = false
      deleted = false
      modifiedColumns = {array} [0]
      virtualColumns = {array} [0]
      user_id = 1
      food_id = 15
      rating = 3
      aFood = {\Food} [34]
      aUser = null
      alreadyInSave = false
      reviewThumbsUpsScheduledForDeletion = null
     1 = {\Review} [14]
      new = false
      deleted = false
      modifiedColumns = {array} [0]
      virtualColumns = {array} [0]
      user_id = 3
      food_id = 15
      rating = 5
      aFood = {\Food} [34]
      aUser = null
      alreadyInSave = false
      reviewThumbsUpsScheduledForDeletion = null
    *Propel\Runtime\Collection\Collection*pluralizer = null
   collReviewsPartial = false
   alreadyInSave = false
   reviewsScheduledForDeletion = null
 *Propel\Runtime\Collection\Collecti4

問題是平均評分不正確。 在virtualColumns中，您可以看到avg_rating字段，其值為“ 5.0000”。 但是，當您看上去較低時，您實際上可以看到該食物有2條評論的評分分別為3和5，因此平均值應為“ 4.0000”。

問題出在哪兒？ 為什么這不能正常工作？

Answer 1

您當前正在對審閱表進行左聯接。 左連接將導致返回幾行（每條評論一個）。 對於返回的每一行，只有一個評論，因此“平均”將與該行的評論分數相同。 按平均值分組不會做很多事情，只會將分數完全相同的評論分組，這不是您要查找的內容。

您應該先按食物ID分組。 然后，您將可以對每個食品獲得一行，並獲得平均評分。

$food = FoodQuery::create()
    ->filterById(15) // constant for testing purposes only
    ->groupById()
    ->leftJoinWithReview()
    ->withColumn("AVG(review.rating)", "avg_rating")
    ->find();