MongoDB:使用Java驱动程序

Question

我在这里学习MongoDB.我坚持使用MongoDB Java驱动程序执行非常基本的操作.我试图从文档中的数组中删除一个元素.该文件如下:

db.test.find().pretty()
{
    "_id" : ObjectId("581245dd51030d389f5cf701"),
    "name" : "Rahul",
    "scores" : [
        {
            "SDM" : 97
        },
        {
            "SE" : 96
        },
        {
            "DM" : 80
        }
    ]
}

我试图删除数组中的第二个元素即{"SE" : 96}.我明白我可以用这个来实现coll.update(match, new BasicDBObject("$pull", update));.但是我想利用这个com.mongodb.client.model.Updates.pull(final String fieldName, final TItem value)方法.

这是我在发布问题之前尝试过的:

1)当我尝试这个时,我没想到会发生任何事情,而且确实没有对文件进行任何修改.

  ` Bson filter = Filters.eq("name", "Rahul");
    Bson delete = Updates.pull("SE", 96);
    collection.updateOne(filter, delete);`

2)以下是抛出异常.

  ` Bson filter = Filters.eq("name", "Rahul");
    Bson delete = Updates.pull("scores.SE", 96);
    collection.updateOne(filter, delete);`

例外:

Exception in thread "main" com.mongodb.MongoWriteException: cannot use the part (scores of scores.SE) to traverse the element ({scores: [ { SDM: 97.0 }, { SE: 96.0 }, { DM: 80.0 } ]})
    at com.mongodb.MongoCollectionImpl.executeSingleWriteRequest(MongoCollectionImpl.java:523)
    at com.mongodb.MongoCollectionImpl.update(MongoCollectionImpl.java:508)
    at com.mongodb.MongoCollectionImpl.updateOne(MongoCollectionImpl.java:355)
    at com.mongodb.MongoCollectionImpl.updateOne(MongoCollectionImpl.java:350)
    at com.mongodb.mongoProject.crud.UpdateTest.main(HW_3_1.java:30)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)

请让我知道我在哪里出错.

谢谢...

Answer 1

试试这个:

Bson delete = Updates.pull("scores", new Document("SE", 96));