2017-05-01 148 views
0

我正在爲使用MongoDb和Morphia的應用程序編寫後端,但我遇到了保存嵌入對象的一個​​有趣問題。Morphia Query在第二次搜索時返回Null,而不是第一次?

假設我在寫論壇軟件。有帖子(父對象)和評論(子對象)。每個帖子包含一個評論的ArrayList。我可以發佈帖子,然後添加一條評論。這工作正常。如果我嘗試添加第二條評論,看起來好像我的Morphia查詢在搜索帖子以附加評論時返回空對象。

下面是代碼,這是我processComment方法中:

// Get Owner and ParentObjectId from the incoming JSONObject. 
     String commentOwner = jsonObject.getString("owner"); 
     String parentObjectUuid = jsonObject.getString("parentObjectUuid"); 

     // Create a new Comment from these values, and add the body. 
     Comment comment = new Comment(commentOwner, parentObjectUuid); 
     comment.setBody(jsonObject.getString("body")); 

     // Get Parent Object from Datastore. 
     Query<Post> query = datastore.createQuery(Post.class); 
     query.field("uuid").equalIgnoreCase(parentObjectUuid); 
     Post parentObject = query.get(); // <--- This is Line #144 where I think it fails. 

     // Add comment to its ParentObject, and save in our datastore. 
     parentObject.addComment(comment); 
     datastore.save(parentObject); 


Here is the stacktrace: 
java.lang.RuntimeException: java.lang.NullPointerException 
    at org.mongodb.morphia.mapping.EmbeddedMapper.fromDBObject(EmbeddedMapper.java:76) 
    at org.mongodb.morphia.mapping.Mapper.readMappedField(Mapper.java:850) 
    at org.mongodb.morphia.mapping.Mapper.fromDb(Mapper.java:282) 
    at org.mongodb.morphia.mapping.Mapper.fromDBObject(Mapper.java:193) 
    at org.mongodb.morphia.query.MorphiaIterator.convertItem(MorphiaIterator.java:134) 
    at org.mongodb.morphia.query.MorphiaIterator.processItem(MorphiaIterator.java:146) 
    at org.mongodb.morphia.query.MorphiaIterator.next(MorphiaIterator.java:117) 
    at org.mongodb.morphia.query.QueryImpl.get(QueryImpl.java:236) 
    at org.mongodb.morphia.query.QueryImpl.get(QueryImpl.java:227) 
    at IncomingProcessor.processComment(IncomingProcessor.java:144) 
    at IncomingProcessor.processIncomingJson(IncomingProcessor.java:78) 
    at IncomingProcessor.<init>(IncomingProcessor.java:50) 
    at Main.main(Main.java:78) 
Caused by: java.lang.NullPointerException 
    at org.mongodb.morphia.Key.hashCode(Key.java:149) 
    at java.util.HashMap.hash(HashMap.java:338) 
    at java.util.HashMap.put(HashMap.java:611) 
    at org.mongodb.morphia.mapping.cache.DefaultEntityCache.notifyExists(DefaultEntityCache.java:82) 
    at org.mongodb.morphia.mapping.cache.DefaultEntityCache.putEntity(DefaultEntityCache.java:90) 
    at org.mongodb.morphia.mapping.Mapper.fromDb(Mapper.java:293) 
    at org.mongodb.morphia.mapping.EmbeddedMapper.readMapOrCollectionOrEntity(EmbeddedMapper.java:210) 
    at org.mongodb.morphia.mapping.EmbeddedMapper.readCollection(EmbeddedMapper.java:144) 
    at org.mongodb.morphia.mapping.EmbeddedMapper.fromDBObject(EmbeddedMapper.java:47) 
    ... 12 more 

只是要清楚,這個代碼工作的第一次。當我嘗試添加第二個評論時,它失敗。 任何想法?謝謝。

+0

IncomingProcessor.processIncomingJson(IncomingProcessor.java:78)'不是NPE嗎? 'jsonObject.getString(「owner」)'對我來說看起來很奇怪 - Morphia應該自動處理它。您不需要手動映射成員變量。 – xeraa

回答

0

Morphia重新保存整個對象,它改變了MongoDB用來識別對象的內部哈希碼。解決問題的代碼如下:

// This gets the Post parent object from the DB. 
Query<Post> query = datastore.createQuery(Post.class).field("uuid").equal(objectUuid); 

// This save the newComment to an ArrayList<Comment> called commentsList. 
datastore.update(query, datastore.createUpdateOperations(Post.class).push("commentsList", newComment)); 

這讓我瘋狂。我正在使用datastore.save()方法,這是錯誤的。我需要使用.push()方法在CreateUpdateOperations上使用datastore.update()方法。

有很多詛咒來到這裏。我不確定我喜歡Morphia。

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