MongoDB：UpdateOne Record

Question

我已經編寫了下列程序，通過刪除最低等級來更新一組記錄。根據程序的輸出，看起來UpdateResult.matchedCount = 1但UpdateResult.ModifiedCount = 0。本質上，查詢是查找要更新的記錄，但不更新記錄。

public static void main(String[] args) { 

     MongoClient client = new MongoClient(); 
     MongoDatabase database = client.getDatabase("school"); 
     MongoCollection<Document> collection = database.getCollection("students"); 

     FindIterable<Document> iterable = collection.find(new Document("scores.type", "homework")).sort(Sorts.orderBy(Sorts.ascending("_id"))); 

     MongoCursor<Document> iterableDocument = iterable.iterator(); 

     while (iterableDocument.hasNext()) { 
      Document wholeDocument = (Document) iterableDocument.next(); 
      List<Document> scores = (List<Document>) wholeDocument.get("scores"); 

      System.out.println("Student id: " + wholeDocument.get("_id")); 
      System.out.println("Student name: " + wholeDocument.get("name")); 

      for (final Document score1 : scores) { 
       for (final Document score2 : scores) { 
        if (score1.get("type").toString().equalsIgnoreCase("homework") && score2.get("type").toString().equalsIgnoreCase("homework")) { 

         Double homeworkScore1 = (Double) score1.get("score"); 
         Double homeworkScore2 = (Double) score2.get("score"); 

         if (homeworkScore1 < homeworkScore2) { 
          BasicDBList homeworkScores = new BasicDBList(); 
          homeworkScores.add(new BasicDBObject("type", "homework").append("score", homeworkScore1)); 
          BasicDBObject lowScoreToRemove = new BasicDBObject("scores", homeworkScores); 

          System.out.println("Lowest Homework score is: " + homeworkScore1); 
          System.out.println("Document that will be updated: " + wholeDocument); 
          System.out.println("Pull Document: " + new Document("$pull", lowScoreToRemove)); 
          UpdateResult result = collection.updateOne(new Document("_id", wholeDocument.get("_id")), new BasicDBObject("$pull", 
            lowScoreToRemove)); 
          System.out.println("UpdateResult: " + result + "\n"); 
         } 
        } 
       } 
      } 
     } 
     iterableDocument.close(); 
    } 

下面是輸出的一個樣本：

Student id: 199 
Student name: Rae Kohout 
Lowest Homework score is: 5.861613903793295 
Document that will be updated: Document{{_id=199, name=Rae Kohout, scores=[Document{{type=exam, score=82.11742562118049}}, Document{{type=quiz, score=49.61295450928224}}, Document{{type=homework, score=28.86823689842918}}, Document{{type=homework, score=5.861613903793295}}]}} 
Pull Document: Document{{$pull={ "scores" : [ { "type" : "homework" , "score" : 5.861613903793295}]}}} 
UpdateResult: AcknowledgedUpdateResult{matchedCount=1, modifiedCount=0, upsertedId=null} 

Answer 1

我蒙戈版本沒有updateOne，但至少從我與「更新」的參數不應該是一個數組的經驗。

So instead of: 
{$pull:{scores:[{type:'homework', score:5.5...}]}}); 
it should be (note the lack of "["): 
{$pull:{scores:{type:'homework', score:5.5...}}}); 

無論如何，注意，有報告的錯誤/約寫結果直觀的特點，所以我建議還可以手動看看你的收藏，看看有什麼被刪除。

Answer 2

查看BasicDBList被註釋掉的代碼行。

public static void main(String[] args) { 

     MongoClient client = new MongoClient(); 
     MongoDatabase database = client.getDatabase("school"); 
     MongoCollection<Document> collection = database.getCollection("students"); 

     FindIterable<Document> iterable = collection.find(new Document("scores.type", "homework")).sort(Sorts.orderBy(Sorts.ascending("_id"))); 

     MongoCursor<Document> iterableDocument = iterable.iterator(); 

     while (iterableDocument.hasNext()) { 
      Document wholeDocument = (Document) iterableDocument.next(); 
      List<Document> scores = (List<Document>) wholeDocument.get("scores"); 

      System.out.println("Student id: " + wholeDocument.get("_id")); 
      System.out.println("Student name: " + wholeDocument.get("name")); 

      for (final Document score1 : scores) { 
       for (final Document score2 : scores) { 
        if (score1.get("type").toString().equalsIgnoreCase("homework") && score2.get("type").toString().equalsIgnoreCase("homework")) { 

         Double homeworkScore1 = (Double) score1.get("score"); 
         Double homeworkScore2 = (Double) score2.get("score"); 

         if (homeworkScore1 < homeworkScore2) { 
          //BasicDBList homeworkScores = new BasicDBList(); 
          //homeworkScores.add(new BasicDBObject("type", "homework").append("score", homeworkScore1)); 
          BasicDBObject lowScoreToRemove = new BasicDBObject("scores", new BasicDBObject("type", "homework").append("score", homeworkScore1)); 

          System.out.println("Lowest Homework score is: " + homeworkScore1); 
          System.out.println("Document that will be updated: " + wholeDocument); 
          System.out.println("Pull Document: " + new Document("$pull", lowScoreToRemove)); 
          UpdateResult result = collection.updateOne(new Document("_id", wholeDocument.get("_id")), new BasicDBObject("$pull", 
            lowScoreToRemove)); 
          //iterable. 
          System.out.println("UpdateResult: " + result + "\n"); 
         } 
        } 
       } 
      } 
     } 
     iterableDocument.close(); 
    }