bot18

## Features The following are new features added in MongoDB 3.6 and supported in the Node.js driver. ### Retryable Writes Support has been added for retryable writes through the connection string. MongoDB 3.6 will utilize server sessions to allow some write commands to specify a transaction ID to enforce at-most-once semantics for the write operation(s) and allow for retrying the operation if the driver fails to obtain a write result (e.g. network error or "not master" error after a replica set failover)Full details can be found in the [Retryable Writes Specification](https://github.com/mongodb/specifications/blob/master/source/retryable-writes/retryable-writes.rst). ### DNS Seedlist Support Support has been added for DNS Seedlists. Users may now configure a single domain to return a list of host names. Full details can be found in the [Seedlist Discovery Specification](https://github.com/mongodb/specifications/blob/master/source/initial-dns-seedlist-discovery/initial-dns-seedlist-discovery.rst). ### Change Streams Support has been added for creating a stream to track changes to a particular collection. This is a new feature in MongoDB 3.6. Full details can be found in the [Change Stream Specification](https://github.com/mongodb/specifications/blob/master/source/change-streams.rst) as well as [examples in the test directory](https://github.com/mongodb/node-mongodb-native/blob/3.0.0/test/functional/operation_changestream_example_tests.js). ### Sessions Version 3.6 of the server introduces the concept of logical sessions for clients. In this driver, `MongoClient` now tracks all sessions created on the client, and explicitly cleans them up upon client close. More information can be found in the [Driver Sessions Specification](https://github.com/mongodb/specifications/blob/master/source/sessions/driver-sessions.rst). ## API Changes We removed the following API methods. - `Db.prototype.authenticate` - `Db.prototype.logout` - `Db.prototype.open` - `Db.prototype.db` - `Db.prototype.close` - `Admin.prototype.authenticate` - `Admin.prototype.logout` - `Admin.prototype.profilingLevel` - `Admin.prototype.setProfilingLevel` - `Admin.prototype.profilingInfo` - `Cursor.prototype.nextObject` We've added the following API methods. - `MongoClient.prototype.logout` - `MongoClient.prototype.isConnected` - `MongoClient.prototype.db` - `MongoClient.prototype.close` - `MongoClient.prototype.connect` - `Db.prototype.profilingLevel` - `Db.prototype.setProfilingLevel` - `Db.prototype.profilingInfo` In core we have removed the possibility of authenticating multiple credentials against the same connection pool. This is to avoid problems with MongoDB 3.6 or higher where all users will reside in the admin database and thus database level authentication is no longer supported. The legacy construct ```js var db = var Db('test', new Server('localhost', 27017)); db.open((err, db) => { // Authenticate db.admin().authenticate('root', 'root', (err, success) => { .... }); }); ``` is replaced with ```js new MongoClient(new Server('localhost', 27017), { user: 'root' , password: 'root' , authSource: 'adming'}).connect((err, client) => { .... }) ``` `MongoClient.connect` works as expected but it returns the MongoClient instance instead of a database object. The legacy operation ```js MongoClient.connect('mongodb://localhost:27017/test', (err, db) => { // Database returned }); ``` is replaced with ```js MongoClient.connect('mongodb://localhost:27017/test', (err, client) => { // Client returned var db = client.db('test'); }); ``` The database specified in the connection string will be set as the default database of the returned client. The default database is now used if no parameter is passed to `MongoClient.prototype.db`, for example: ```js MongoClient.connect('mongodb://localhost:27017/test') .then(client => client.db().collection('foo').insert({ a: 42 }) .then(() => ...) .catc(err => ...); ``` ## Other Changes Below are more updates to the driver in the 3.0.0 release. ### Connection String Following [changes to the MongoDB connection string specification](https://github.com/mongodb/specifications/commit/4631ccd4f825fb1a3aba204510023f9b4d193a05), authentication and hostname details in connection strings must now be URL-encoded. These changes reduce ambiguity in connection strings. For example, whereas before `mongodb://u$ername:pa$$w{}rd@/tmp/mongodb-27017.sock/test` would have been a valid connection string (with username `u$ername`, password `pa$$w{}rd`, host `/tmp/mongodb-27017.sock` and auth database `test`), the connection string for those details would now have to be provided to MongoClient as `mongodb://u%24ername:pa%24%24w%7B%7Drd@%2Ftmp%2Fmongodb-27017.sock/test`. Unsupported URL options in a connection string now log a warning instead of throwing an error. For more information about connection strings, read the [connection string specification](https://github.com/mongodb/specifications/blob/master/source/connection-string/connection-string-spec.rst). ### `BulkWriteResult` & `BulkWriteError` When errors occured with bulk write operations in the past, the driver would callback or reject with the first write error, as well as passing the resulting `BulkWriteResult`. For example: ```js MongoClient.connect('mongodb://localhost', function(err, client) { const collection = client.db('foo').collection('test-collection') collection .insert({ id: 1 }) .then(() => collection.insertMany([ { id: 1 }, { id: 1 } ])) .then(result => /* deal with errors in `result */) .catch(err => /* no error is thrown for bulk errors */); }); ``` becomes: ```js MongoClient.connect('mongodb://localhost', function(err, client) { const collection = client.db('foo').collection('test-collection') collection .insert({ id: 1 }) .then(() => collection.insertMany([ { id: 1 }, { id: 1 } ])) .then(() => /* this will not be called in the event of a bulk write error */) .catch(err => /* deal with errors in `err` */); }); ``` Where the result of the failed operation is a `BulkWriteError` which has a child value `result` which is the original `BulkWriteResult`. Similarly, the callback form no longer calls back with an `(Error, BulkWriteResult)`, but instead just a `(BulkWriteError)`. ### `mapReduce` inlined results When `Collection.prototype.mapReduce` is invoked with a callback that includes `out: 'inline'`, it would diverge from the `Promise`-based variant by returning additional data as positional arguments to the callback (`(err, result, stats, ...)`). This is no longer the case, both variants of the method will now return a single object for all results - a single value for the default case, and an object similar to the existing `Promise` form for cases where there is more data to pass to the user. ### Find `find` and `findOne` no longer support the `fields` parameter. You can achieve the same results as the `fields` parameter by using `Cursor.prototype.project` or by passing the `projection` property in on the options object . Additionally, `find` does not support individual options like `skip` and `limit` as positional parameters. You must either pass in these parameters in the `options` object, or add them via `Cursor` methods like `Cursor.prototype.skip`. 2.x syntax: ```js const cursor = coll.find({ a: 42 }, { someField: 1 }); ``` 3.x syntax: ``` const cursor = coll.find({ a: 42 }).project({ someField: 1 }); /* OR */ const cursor = coll.find({ a: 42 }, { projection: { someField: 1 } }); ``` ### `Collection.prototype.aggregate` `Collection.prototype.aggregate` no longer accepts variadic arguments. While this was originally added to improve compatibility with the mongo shell, it has never been a documented feature, and has led to more bugs and maintenance burden. Pipeline stages are now only accepted as an `Array` of stages as the first argument. 2.x syntax: ```js collection.prototype.aggregate( {$match: {a: 1}}, {$project: {b: 1, _id: 0}}, function (err, result) { ... } ); ``` 3.x syntax ```js collection.prototype.aggregate( [ {$match: {a: 1}}, {$project: {b: 1, _id: 0}} ], function (err, cursor) { ... } ); ``` `Collection.prototype.aggregate` now returns a cursor if a callback is provided. It used to return the resulting documents which is the same as calling `cursor.toArray()` on the cursor we now pass to the callback. 2.x syntax ```js collection.prototype.aggregate( [ {$match: {a: 1}}, {$project: {b: 1, _id: 0}} ], function (err, result) { console.log(result); } ); ``` 3.x syntax ```js collection.prototype.aggregate( [ {$match: {a: 1}}, {$project: {b: 1, _id: 0}} ], function (err, cursor) { cursor.toArray(function(err, result) { console.log(result); }); } ); ``` Support added for `comment` in the aggregation command. Support also added for a `hint` field in the aggregation `options`. If you use aggregation and try to use the `explain` flag while you have a `readConcern` or `writeConcern`, your query will now fail. ### `updateOne` & `updateMany` The driver now ensures that updated documents contain atomic operators. For instance, if a user tries to update an existing document but passes in no operations (such as `$set`, `$unset`, or `$rename`), the driver will now error: ```js let testCollection = db.collection('test'); testCollection.updateOne({_id: 'test'}, {}); // An error is returned: The update operation document must contain at least one atomic operator. ``` ### `keepAlive` Wherever it occurs, the option `keepAlive` has been changed. `keepAlive` is now a boolean that enables/disables `keepAlive`, while `keepAliveInitialDelay` specifies how long to wait before initiating keepAlive. This brings the API in line with [NodeJS's socket api](https://nodejs.org/dist/latest-v9.x/docs/api/all.html#net_socket_setkeepalive_enable_initialdelay) ### `insertMany` Now `insertMany` returns `insertedIds` in a map of the index of the inserted document to the id of the inserted document: ```js { "0": 2, "1": 3 } ``` Previously an array of ids was returned: `[ 2, 3 ]`. This change occurs with both ordered and unordered `insertMany` calls, see the [CRUD specifications](https://github.com/mongodb/specifications/blob/master/source/crud/crud.rst#results) for more details. ### `geoNear` command helper The functionality of the geoNear command is duplicated elsewhere in the language, in the `$near`/`$nearSphere` query operators on unsharded collections, and in the `$geoNear` aggregation stage on all collections. Maintaining this command increases our test surface, and creates additional work when adding features that must be supported on all read commands. As a result, the command will be fully removed in the MongoDB 4.0 release, and we are choosing to remove it in this major release of the node driver. ### Tests We have updated all of the tests to use [Mocha](https://mochajs.org) and a new test runner, [`mongodb-test-runner`](https://github.com/mongodb-js/mongodb-test-runner), which sets up topologies for the test scenarios.