What's New新增功能¶

Node.js Version¶

The minimum supported version of Node.js is now v12.9 or greater for version 4 of the driver. 对于驱动程序版本4，Node.js的最低支持版本现在是v12.9或更高版本。Support for our 3.x branches will continue until summer 2022 to allow time to upgrade.对我们3.x分支的支持将持续到2022年夏季，以便有时间升级。

Cursor Improvements游标改进¶

Our Cursor implentation is now updated to make it clear what is possible before and after execution of an operation.我们的游标实现现在已经更新，以明确在执行操作之前和之后可以做什么。

const fc = collection.find({a: 2.3}).skip(1)
for await (const doc of fc) {
  console.log(doc)
  fc.limit(1) // incorrect usage, cursor already executing
}

There was inconsistency surrounding how the cursor would error if a setting was applied after cursor execution began. 如果在游标执行开始后应用设置，则游标将如何出错，存在不一致性。Now, the cursor will throw an error when attempting to apply operations in an invalid state, similar to the following:现在，当尝试在无效状态下应用操作时，光标将抛出一个错误，如下所示：

MongoError: Cursor is already initialized

• Affected classes:受影响类别：
  • AbstractCursor
  • FindCursor
  • AggregationCursor
  • ChangeStreamCursor (This is the underlying cursor for ChangeStream)（这是ChangeStream的基础游标）
  • ListCollectionsCursor

const cursor = collection.find({})
const stream = cursor.stream()
stream.on("data", data=> console.log)
stream.on("error", () => client.close())

MongoClientOptions Interface¶

With type hinting, you should find that options passed to a MongoClient are enumerated and discoverable. We've made a large effort to process all options in the driver to give early warnings about incompatible settings to get your app up and running in a correct state quickly.

• checkServerIdentity is no longer checked before being passed to the underlying Node API. Previously, accepted values were false, or a function. Now, the argument must be a function. Specifying a boolean will result in an error being thrown.
• It is longer required to specify useUnifiedTopology or useNewUrlParser.

createCollection()¶

This method no longer supports a strict option, which returned an error if the collection did not exist. To assert the existence of a collection, use the listCollections() method instead.

const collections = (await db.listCollections({}, { nameOnly: true })
  .toArray()).map(
    ({name}) => name
  );
if (!collections.includes(myNewCollectionName)) {
  throw new Error(`${myNewCollectionName}doesn't exist`);
}

BulkWriteError → MongoBulkWriteError¶

BulkWriteError is now renamed to MongoBulkWriteError.

When running bulk operations that make writes you can encounter errors depending on your settings. Import the new class name MongoBulkWriteError when testing for errors in bulk operations.

DB¶

DB is no longer an EventEmitter. Listen for events directly from your MongoClient instance.

Collection.group()¶

The Collection.group() helper, deprecated since MongoDB 3.4, is now removed. Use the aggregation pipeline $group operator instead.

Authentication¶

• gssapiServiceName is now removed. Use authMechanismProperties.SERVICE_NAME in the URI or as an option on MongoClientOptions.
  Example

  ?authMechanismProperties.SERVICE_NAME
  // or
  new MongoClient(url, { SERVICE_NAME: "alternateServiceName" })
• Specifying username and password as options is only supported in the URI or as an option on MongoClientOptions.仅在URI中或MongoClient上支持将用户名和密码指定为选项。
  Example

  new MongoClient("mongodb://username:password@<host><port>")
  // or
  new MongoClient(url, { auth: { username: "<>", password: "<>" } })

GridStore Removal¶

The GridStore API (already deprecated in 3.x) is now replaced with GridFSBucket. GridStoreAPI（在3.x中已经弃用）现在被GridFSBucket取代。For more information on GridFS, see the mongodb manual.有关GridFS的更多信息，请参阅mongodb手册。

Below are some snippets that represent equivalent operations.下面是一些表示等效操作的代码段。

// old way
const gs = new GridStore(db, filename, mode[, options])
// new way
const bucket = new GridFSBucket(client.db('test')[,options])

bucket.openDownloadStreamByName(filename, { start: 0, end: 100 })

await client.connect();
const filename = 'test.txt'; // whatever local file name you want您想要的任何本地文件名
const db = client.db();
const bucket = new GridFSBucket(db);

fs.createReadStream(filename)
  .pipe(bucket.openUploadStream(filename))
  .on('error', console.error)
  .on('finish', () => {
    console.log('done writing to db!');

    bucket
      .find()
      .toArray()
      .then(files => {
        console.log(files);

        bucket
          .openDownloadStreamByName(filename)
          .pipe(fs.createWriteStream('downloaded_' + filename))
          .on('error', console.error)
          .on('finish', () => {
            console.log('done downloading!');
            client.close();
          });
      });
  });

// old way
GridStore.unlink(db, name, callback);
// new way
bucket.delete(file_id);

const fileMetaDataList: GridFSFile[] = bucket.find({}).toArray();

Unified Topology¶

• We internally now only manage a unifiedTopology when you connect to a mongod. The differences between this and previous versions is detailed here.
• It is longer required to specify useUnifiedTopology or useNewUrlParser.
• You must use the new directConnection option to connect to unitiliazed replica set members.

Explain¶

Support is now added for fine-grained verbosity modes. You can learn more about each mode here.

Command Monitoring¶

The instrument() method is now removed. Use command monitoring instead. See our guide on command monitoring for more information.