mgo r2016.02.04

This is one of the most packed releases of the mgo driver for Go in recent times. There are new features, important fixes, and relevant
internal reestructuring to support the on-going server improvements.

As usual for the driver, compatibility is being preserved both with old applications and with old servers, so updating should be a smooth experience.

Release r2016.02.04 of mgo includes the following changes which were requested, proposed, and performed by a great community.


Exposed access to individual bulk error cases

Accessing the individual errors obtained while attempting a set of bulk operations is now possible via the new mgo.BulkError error type and its Cases method which returns a slice of mgo.BulkErrorCases which are properly indexed according to the operation order used. There are documented server limitations for MongoDB version 2.4 and older.

This change completes the bulk API. It can now perform optimized bulk queries when communicating with recent servers (MongoDB 2.6+), perform the same operations in older servers using compatible but less performant options, and in both cases provide more details about obtained errors.

Feature first requested by pjebs.

New fields in CollectionInfo

The CollectionInfo type has new fields for dealing with the recently introduced document validation MongoDB feature, and also the storage engine-specific options.

Features requested by nexcode and pjebs.

New Find and GetMore command support

MongoDB is moving towards replacing the old wire protocol with a command-based based implementation, and every recent release introduced changes around that. This release of mgo introduces support for the find and getMore commands which were added to MongoDB 3.2. These are exercised whenever querying the database or iterating over queried results.

Previous server releases will continue to use the classical mechanism, and the two approaches should be compatible. Please report any issues in that regard.

Do not fallback to Monotonic mode improperly

Recent driver changes adapted the Pipe.Iter, Collection.Indexes, and Database.CollectionNames methods to work with recent server releases. These changes also introduced a bug that could cause the driver to talk to a secondary server improperly, when that operation was the first operation performed on the session. This has been fixed.

Problem reported by Sundar.

Fix crash in new bulk update API

The new methods introduced in the bulk update API in the last release were crashing when a connection error occurred.

Fix contributed by Maciej Galkowski.

Enable TCP keep-alives for all connections

As requested by developers, TCP keep-alives are now enabled for all connections. No timing is specified, so the default operating system setting will be used.

Feature requested by Hunor Kovács, Berni Varga, and Martin Garton.

ChangeInfo.Updated now behaves as documented

The ChangeInfo.Updated field is documented to report the number of documents that were changed, but in fact that was not possible in old releases of the driver, since the server did not provide that information. Instead, the server only reported the number of documents matched by the selection document.

This has been fixed, so starting with MongoDB 2.6, the driver will behave as documented, and inform the number of documents that were indeed updated. This is related to the next driver change:

New ChangeInfo.Matched field

The new ChangeInfo.Matched field will report the number of documents that matched the selection document, whether the performed change was a removal, an update, or an upsert.

Feature requested by Žygimantas and other list members.

ObjectId now supports TextMarshaler/TextUnmarshaler

ObjectId now knows how to marshal/unmarshal itself as text in hex format when using its encoding.TextMarshaler and TextUnmarshaler interfaces.

Contributed by Jack Spirou.

Created GridFS index is now unique

The index on {“files_id”, “n”} automatically created for GridFS chunks when a file write completes now enforces the uniqueness of the key.

Contributed by Wisdom Omuya.

Use SIGINT in dbtest.DBServer

The dbtest.DBServer was stopping the server with SIGKILL, which would not give it enough time for a clean shutdown. It will now stop it with SIGINT.

Contributed by Haijun Wang.

Ancient field tag logic dropped

The very old field tag format parser, in use several years back even before Go 1 was released, was still around in the code base for no benefit.

This has been removed by Alexandre Cesaro.

Documentation improvements

Documentation improvements were contributed by David Glasser, Ryan Chipman, and Shawn Smith.

Fixed BSON skipping of incorrect slice types

The BSON parser was collapsing when an array value was unmarshaled into an existing field that was not of an appropriate type for such values. This has been fixed so that the the bogus field is ignored and the value skipped.

Fix contributed by Gabriel Russel.

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