Morphia（MongoDB）Datastore「get」返回null

Question

所以我開始與Morphia一起工作，遇到一個奇怪的問題。

這裏是我的實體類

@Entity("movies") 
@Indexes(@Index(value = "Name", fields = @Field("Name"))) 
@Converters(LocalDateConverter.class) 
public class MovieDetails implements Serializable 
{ 
    @Id 
    public String Id; 
    public String Name; 
    public String Description; 
    public String ImageName; 
    public LocalDate ReleaseDate; 
    public String Director; 
    public int Duration; 
    public String Genres; 
    public String Actors; 

    public MovieDetails() 
    { 

    } 

    public MovieDetails(String id, String name, String description, String imageName, String director, String actors, LocalDate releaseDate, String genres, int duration) 
    { 
     this (name, description, imageName, director, actors, releaseDate, genres, duration); 
     Id = id; 
    } 

    public MovieDetails(String name, String description, String imageName, String director, String actors, LocalDate releaseDate, String genres, int duration) 
    { 
     Name = name; 
     Description = description; 
     ImageName = imageName; 
     Director = director; 
     Actors = actors; 
     ReleaseDate = releaseDate; 
     Genres = genres; 
     Duration = duration; 
    } 
} 

這是我的小測試：

final Morphia morphia = new Morphia(); 

// tell Morphia where to find your classes 
// can be called multiple times with different packages or classes 
morphia.mapPackage("nimrodpasha.cinema.objects"); 

// create the Datastore connecting to the default port on the local host 
final Datastore datastore = 
     morphia.createDatastore(SingleMongoClient.getInstance().getClient(), 
           Constants.DB.TICKET_DATABASE); 
datastore.ensureIndexes(); 

    //region new movie 
    MovieDetails movie = new MovieDetails("The Mask", "Stanley Ipkiss (Jim Carrey) is a bank clerk that is an incredibly nice man. Unfortunately," + 
      " he is too nice for his own good and is a pushover when it comes to confrontations. After one of the worst days of his life, he finds a mask that depicts Loki, " + 
      "the Norse night god of mischief. Now, when he puts it on, he becomes his inner, self: a cartoon romantic wild man. However, a small time crime boss, Dorian Tyrel (Peter Greene), " + 
      "comes across this character dubbed The Mask by the media. After Ipkiss's alter ego indirectly kills his friend in crime," + 
      " Tyrel now wants this green-faced goon destroyed.", 
              "MASK.jpg", "Chuck Russell", "Jim Carrey as Stanley Ipkiss/The Mask,Cameron Diaz as Tina Carlyle,Amy Yasbeck as Peggy Brandt,Joely Fisher as Maggie", new LocalDate(1994, 2, 1), "Action,Comedy,CrimeAction,Family,Fantasy", 88); 
    //endregion 

// Clearing the db first 
datastore.delete(datastore.createQuery(MovieDetails.class)); 

// Saving a new entity and getting the result saved id 
String id = (String) datastore.save(movie).getId(); 

// This returns as null 
MovieDetails movieRetrieved = datastore.get(MovieDetails.class, id); 

// This returns with one item 
List<MovieDetails> allMovies = datastore.createQuery(MovieDetails.class).asList(); 

當我使用

datastore.get（MovieDetails.class，ID）

我得到空

當我使用：

datastore.createQuery（MovieDetails.class）.asList（）;

我確實在數據庫中看到了我的影片，並在get函數中使用了Id。

嘗試了很多變化中的id ... toString（），ObjectId（id），Key（從保存結果返回的值）。

中的id DB（與蒙戈Explorer查看）確實顯示的東西是不是字符串（藍色），可疑： Mongo Explorer item picture

任何想法？

編輯： *的標識確實是一個字符串，演員的作品，用手錶+的instanceof 編輯2可以證實： *不知怎的，劇組從的ObjectId到字符串傳遞和ID wasnt真串。

Answer 1

After Nic Cottrell（謝謝！）回答我對問題有了新的認識。 由於我的@Id字段沒有被我分配，所以它在數據庫中被自動分配爲ObjectId。 因爲我仍然想使用字符串，我只是在創建對象時指定了@Id字段。

Id = ObjectId.get().toString(); 

發現瞭解決方案： MongoDB/Morphia saves technical id as ObjectId although it's a String in Java

Answer 2

我會將你的I字段從字符串更改爲一個BSON ObjectId字段，MongoDB將在保存時自動分配這個字段。如果你使用ObjectId作爲參數進行調用，它應該可以工作。強烈建議在Mongo中使用ObjectId作爲您的ID字段。

我在猜測Morphia正試圖將一個ObjectId編組到你的字符串ID字段中，並且在某處存在一個小錯誤。我會嘗試撥打datastore.get(Example.class, new ObjectId(id)）。