MongoDB Java客户端的WriteConcern不起作用 [英] MongoDB java client's WriteConcern doesn't work

问题描述

我是使用MongoDB的新手.我刚刚通过Maven导入了最新的MongoDB Java客户端:

I am a newbie to use MongoDB. I just imported the latest MongoDB java client via Maven:

    <dependency>
        <groupId>org.mongodb</groupId>
        <artifactId>mongo-java-driver</artifactId>
        <version>3.2.2</version>
    </dependency>

然后，我编写了一个非常简单的程序来测试插入操作.

And then I wrote a very simple program to test the insert operation.

        //I use a replicaset
    MongoClient mongoClient = new MongoClient(
            Arrays.asList(new ServerAddress("10.12.16.136", 29017),
                    new ServerAddress("10.12.16.136", 29018),
                    new ServerAddress("10.12.16.136", 29019)));

    //I just want to write and ignore any database errors. (This does not work)
    mongoClient.setWriteConcern(WriteConcern.UNACKNOWLEDGED);

    //Get database and collection
    MongoDatabase database = mongoClient.getDatabase("test");
    MongoCollection<Document> collection = database.getCollection("realtime");

    //This does not work too.
    collection.withWriteConcern(WriteConcern.UNACKNOWLEDGED);

    //Make a simple object to insert. I already have a document with the same _id in the database and I don't want to see the exception via the WriteConcern operation.
    Document doc = Document("longitude", longitude)
            .append("latitude", latitude)
            .append("velocity", velocity)
            .append("soc", soc)
            .append("_id", 12345678);

    //WriteConcern.UNACKNOWLEDGED doesn't work. An exception will be raised.
    collection.insertOne(doc);

我该怎么做正确的事?

推荐答案

这是因为collection.withWriteConcern(WriteConcern.UNACKNOWLEDGED);生成了一个新的MongoCollection对象，该对象具有不同的写顾虑，而您从未使用过:

That's because collection.withWriteConcern(WriteConcern.UNACKNOWLEDGED); generates a new MongoCollection object with a different write concern which you never use:

/** *创建一个具有不同写入关注点的新MongoCollection实例. * * @param writeConcern集合的新{@link com.mongodb.WriteConcern} * @返回具有不同writeConcern的新MongoCollection实例 */

/** * Create a new MongoCollection instance with a different write concern. * * @param writeConcern the new {@link com.mongodb.WriteConcern} for the collection * @return a new MongoCollection instance with the different writeConcern */

MongoCollection withWriteConcern(WriteConcern writeConcern);

以下代码:

MongoCollection<Document> dup = collection.withWriteConcern(WriteConcern.UNACKNOWLEDGED);
...
dup.insertOne(doc);

应该可以工作，即没有出现错误.

should work, i.e. no error raised.

关于MongoClient级别的写关注，它不会传播到数据库:

As for the MongoClient level write concern which is not propagated to the database:

public MongoDatabase getDatabase(final String databaseName) {
    MongoClientOptions clientOptions = getMongoClientOptions();
    return new MongoDatabaseImpl(databaseName, clientOptions.getCodecRegistry(), clientOptions.getReadPreference(),
            clientOptions.getWriteConcern(), createOperationExecutor());
}

如您所见，写关注点来自MongoClientOptions，而忽略了传递给mongoClient.setWriteConcern()方法的参数值，这可能是一个错误.

As you can see, the write concern is taken from MongoClientOptions ignoring the parameter value passed to mongoClient.setWriteConcern() method, which may be a bug.

因此，要正确设置全局写关注点，您将必须创建MongoClientOptions的实例:

So, to set a global write concern properly, you will have to create an instance of MongoClientOptions:

 MongoClientOptions options = MongoClientOptions
     .builder()
     .writeConcern(WriteConcern.UNACKNOWLEDGED)
     .build();

并将其传递给MongoClient构造函数.

and pass it to the MongoClient constructor.

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