MongoDB java 客户端的 WriteConcern 不起作用

Question

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：

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

然后我写了一个非常简单的程序来测试插入操作。

        //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);

我怎样才能做正确的事？

Answer 1

那是因为collection.withWriteConcern(WriteConcern.UNACKNOWLEDGED);生成一个MongoCollection具有不同写入问题的新对象，而您从未使用过：

/** * 使用不同的写关注创建一个新的 MongoCollection 实例。* * @param writeConcern 集合的新 {@link com.mongodb.WriteConcern} * @return 具有不同 writeConcern 的新 MongoCollection 实例 */

MongoCollection withWriteConcern(WriteConcern writeConcern);

以下代码：

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

应该工作，即没有出现错误。

至于MongoClient未传播到数据库的级别写关注：

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

如您所见，写入问题来自MongoClientOptions忽略传递给mongoClient.setWriteConcern()方法的参数值，这可能是一个错误。

因此，要正确设置全局写入问题，您必须创建一个实例MongoClientOptions：

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

并将其传递给MongoClient构造函数。