Provided by: libmongodb-perl_2.2.2-2_all 
NAME
MongoDB::Upgrading::v1 - Deprecations and behavior changes from v0 to v1
VERSION
version v2.2.2
DESCRIPTION
The v1 driver represents a substantial step forward in functionality and consistency. There are many
areas where the old API has been deprecated or changed in a backward breaking way.
This document is intended to help developers update their code to take into account API changes from the
v0 driver to the v1 driver.
RATIONALE
Changes to the driver were deemed necessary to achieve certain goals:
• consistency (intra-driver) – many parts of the v0 API were inconsistent, behaving differently from
method to method; the v1 API minimizes developer surprises by improving consistency in return types
and exception mechanisms.
• consistency (inter-driver) — "next-generation" MongoDB drivers across all languages are converging on
common APIs and common behaviors; this simplifies developer education and support, as cross-language
examples will be similar.
• encapsulation – too many low-level, internal operations were exposed as part of the API, which
complicates maintenance work; the v1 API aims to minimize the "public surface" available to
developers, allowing faster future development keeping up with MongoDB server enhancements with less
risk of breakage.
• abstraction – many v0 methods returned raw server documents for end-user code to inspect, which is
brittle in the face of changes in server responses over time; the v1 API uses result classes to
abstract the details behind standardized accessors.
• server compatibility – some new features and behavior changes in the MongoDB server no longer fit the
old driver design; the v1 driver transparently supports both old and new servers.
• portability – the v0 driver had a large dependency tree and substantial non-portable C code; the v1
driver removes some dependencies and uses widely-used, well-tested CPAN modules in place of custom C
code where possible; it lays the groundwork for a future "pure-Perl optional" driver.
• round-trippable data – the v0 BSON implementation could easily change data types when round-tripping
documents; the v1 driver is designed to round-trip data correctly whenever possible (within the
limits of Perl's dynamic typing).
INSTALLATION AND DEPENDENCY CHANGES
Moo instead of Moose
The v1 driver uses Moo instead of Moose. This change results in a slightly faster driver and a
significantly reduced deep dependency tree.
SSL and SASL
The v0 driver required a compiler and OpenSSL and libgsasl for SSL and SASL support, respectively. The
v1 driver instead relies on CPAN modules "IO::Socket::SSL" and "Authen::SASL" for SSL and SASL support,
respectively.
SSL configuration is now possible via the ssl attribute.
Authentication configuration is described in "AUTHENTICATION" in MongoDB::MongoClient.
BEHAVIOR CHANGES
MongoClient configuration
New configuration options
Several configuration options have been added, with particular emphasis on adding more granular control
of timings and timeout behaviors.
• "auth_mechanism"
• "auth_mechanism_properties"
• "bson_codec"
• "connect_timeout_ms"
• "heartbeat_frequency_ms"
• "local_threshold_ms"
• "max_time_ms"
• "replica_set_name"
• "read_pref_mode"
• "read_pref_tag_sets"
• "server_selection_timeout_ms"
• "socket_check_interval_ms"
• "socket_timeout_ms"
Replica set configuration
Connecting to a replica set now requires a replica set name, given either with the "replica_set_name"
option for MongoDB::MongoClient or with the "replicaSet" option in a connection string. For example:
$client = MongoDB::MongoClient->new(
host => "mongodb://rs1.example.com,rs2.example.com/",
replica_set_name => 'the_set',
);
$client = MongoDB::MongoClient->new(
host => "mongodb://rs1.example.com,rs2.example.com/?replicaSet=the_set"
);
Configuration options changed to read-only
Configuration options are changing to be immutable to prevent surprising action-at-a-distance. (E.g.
changing an attribute value in some part of the code changes it for other parts of the code that didn't
expect it.) Going forward, options may be set at MongoDB::MongoClient construction time only.
The following options have changed to be read-only:
• "db_name"
• "j"
• "password"
• "ssl"
• "username"
• "w"
• "wtimeout"
Write concern may be overridden at the MongoDB::Database and MongoDB::Collection level during
construction of those objects. For more details, see the later section on write concern changes.
Mapping between connection string and configuration options
Many configuration options may be set via a connection string URI in the "host" option. In the v0
driver, the precedence between the connection string and constructor options was completely inconsistent.
In the v1 driver, options set via a connection string URI will take precedence over options passed to the
constructor. This is consistent with with other MongoDB drivers (as well as how DBI treats Data Source
Names).
The list of servers and ports as well as the optional "username", "password" and "db_name" options come
directly from URI structure. Other options are parsed as key-value parameters at the end of the
connection string. The following table shows how connection string keys map to configuration options in
the MongoDB::MongoClient:
Connection String Key MongoClient option
--------------------------- -----------------------------
authMechanism auth_mechanism
authMechanismProperties auth_mechanism_properties
connectTimeoutMS connect_timeout_ms
heartbeatFrequencyMS heartbeat_frequency_ms
journal j
localThresholdMS local_threshold_ms
maxTimeMS max_time_ms
readPreference read_pref_mode
readPreferenceTags read_pref_tag_sets
replicaSet replica_set_name
serverSelectionTimeoutMS server_selection_timeout_ms
socketCheckIntervalMS socket_check_interval_ms
socketTimeoutMS socket_timeout_ms
ssl ssl
w w
wTimeoutMS wtimeout
The "readPreferenceTags" and "authMechanismProperties" keys take colon-delimited, comma-separated pairs:
readPreferenceTags=dc:nyeast,rack:1
authMechanismProperties=SERVICE_NAME:mongodb
The "readPreferenceTags" option may be repeated to build up a list of tag set documents:
readPreferenceTags=dc:nyc,rack:1&readPreferenceTags=dc:nyc
Deprecated configuration options
Several options have been superseded, replaced or renamed for clarity and are thus deprecated and
undocumented. They are kept for a limited degree of backwards compatibility. They will be generally be
used as fallbacks for other options. If any were read-write, they have also been changed to read-only.
• "dt_type" — see "BSON encoding changes" for details.
• "query_timeout" — replaced by "socket_timeout_ms"; if set, this will be used as a fallback default
for "socket_timeout_ms".
• "sasl" — superseded by "auth_mechanism"; if set, this will be used along with "sasl_mechanism" as a
fallback default for "auth_mechanism".
• "sasl_mechanism" — superseded by "auth_mechanism"; if set, this will be used as a fallback default
for "auth_mechanism".
• "timeout" — replaced by "connect_timeout_ms"; if set, this will be used as a fallback default for
"connect_timeout_ms".
These will be removed in a future major release.
Configuration options removed
Some configuration options have been removed entirely, as they no longer serve any purpose given changes
to server discovery, server selection and connection handling:
• "auto_connect"
• "auto_reconnect"
• "find_master"
• "max_bson_size"
As described further below in the "BSON encoding changes" section, these BSON encoding configuration
options have been removed as well:
• "inflate_dbrefs"
• "inflate_regexps"
Removed configuration options will be ignored if passed to the MongoDB::MongoClient constructor.
Lazy connections and reconnections on demand
The improved approach to server monitoring and selection allows all connections to be lazy. When the
client is constructed, no connections are made until the first network operation is needed. At that
time, the client will scan all servers in the seed list and begin regular monitoring. Connections that
drop will be re-established when needed.
IMPORTANT: Code that used to rely on a fatal exception from "MongoDB::MongoClient->new" when no mongod is
available will break. Instead, users are advised to just conduct their operations and be prepared to
handle errors.
For testing, users may wish to run a simple command to check that a mongod is ready:
use Test::More;
# OLD WAY: BROKEN
plan skip_all => 'no mongod' unless eval {
MongoDB::MongoClient->new
};
# NEW WAY 1: with MongoDB::MongoClient
plan skip_all => 'no mongod' unless eval {
MongoDB::MongoClient->new->db('admin')->run_command(
[ ismaster => 1 ]
)
};
# NEW WAY 2: with MongoDB and connect
plan skip_all => 'no mongod' unless eval {
MongoDB->connect->db('admin')->run_command([ ismaster => 1 ])
};
See SERVER SELECTION and SERVER MONITORING AND FAILOVER in MongoDB::MongoClient for details.
Exceptions are the preferred error handling approach
In the v0 driver, errors could be indicated in various ways:
• boolean return value
• string return value is an error; hash ref is success
• document that might contain an 'err', 'errmsg' or '$err' field
• thrown string exception
Regardless of the documented error handling, every method that involved a network operation would throw
an exception on various network errors.
In the v1 driver, exceptions objects are the standard way of indicating errors. The exception hierarchy
is described in MongoDB::Error.
Cursors and query responses
In v0, MongoDB::Cursor objects were used for ordinary queries as well as the query-like commands
aggregation and parallel scan. However, only cursor iteration commands worked for aggregation and
parallel scan "cursors"; the rest of the MongoDB::Cursor API didn't apply and was fatal.
In v1, all result iteration is done via the new MongoDB::QueryResult class. MongoDB::Cursor is now just
a thin wrapper that holds query parameters, instantiates a MongoDB::QueryResult on demand, and passes
iteration methods through to the query result object.
This significantly simplifies the code base and should have little end-user visibility unless users are
specifically checking the return type of queries and query-like methods.
The "explain" cursor method no longer resets the cursor.
The "slave_okay" cursor method now sets the "read_preference" to 'secondaryPreferred' or clears it to
'primary'.
The "snapshot" cursor method now requires a boolean argument, allowing it to be turned on or off before
executing the query. Calling it without an argument (as it was in v0) is a fatal exception.
Parallel scan "cursors" are now QueryResult objects, with the same iteration methods as in v0.
The $MongoDB::Cursor::slave_okay global variable has been removed as part of the revision to read
preference handling. See the read preferences section below for more details.
The $MongoDB::Cursor::timeout global variable has also been removed. Timeouts are set during
MongoDB::MongoClient configuration and are immutable. See the section on configuration changes for more.
Aggregation API
On MongoDB 2.6 or later, "aggregate" always uses a cursor to execute the query. The "batchSize" option
has been added (but has no effect prior to 2.6). The "cursor" option is deprecated.
The return types for the "aggregate" method are now always QueryResult objects, regardless of whether the
aggregation uses a cursor internally or is an 'explain'.
NOTE: To help users with a 2.6 mongos and mixed version shards with versions before 2.6, passing the
deprecated 'cursor' option with a false value will disable the use of a cursor. This workaround is
provided for convenience and will be removed when 2.4 is no longer supported.
Read preference objects and the read_preference method
A new MongoDB::ReadPreference class is used to encapsulate read preference attributes. In the v1 driver,
it is constructed from the "read_pref_mode" and "read_pref_tag_sets" attributes on MongoDB::MongoClient:
MongoDB::MongoClient->new(
read_pref_mode => 'primaryPreferred',
read_pref_tag_sets => [ { dc => 'useast' }, {} ],
);
The old "read_preference" method to change the read preference has been removed and trying to set a read
preference after the client has been created is a fatal error. The old mode constants PRIMARY,
SECONDARY, etc. have been removed.
The "read_preference" method now returns the MongoDB::ReadPreference object generated from
"read_pref_mode" and "read_pref_tag_sets".
It is inherited by MongoDB::Database, MongoDB::Collection, and MongoDB::GridFS objects unless provided as
an option to the relevant factory methods:
my $coll = $db->get_collection(
"foo", { read_preference => 'secondary' }
);
Such "read_preference" arguments may be a MongoDB::ReadPreference object, a hash reference of arguments
to construct one, or a string that represents the read preference mode.
MongoDB::Database and MongoDB::Collection also have "clone" methods that allow easy alteration of a read
preference for a limited scope.
my $coll2 = $coll->clone( read_preference => 'secondaryPreferred' );
For MongoDB::Cursor, the "read_preference" method sets a hidden read preference attribute that is used
for the query in place of the MongoDB::MongoClient default "read_preference" attribute. This means that
calling "read_preference" on a cursor object no longer changes the read preference globally on the client
– the read preference change is scoped to the cursor object only.
Write concern objects and removing the safe argument
A new MongoDB::WriteConcern class is used to encapsulate write concern attributes. In the v1 driver, it
is constructed from the "w", "wtimeout" and "j" attributes on MongoDB::MongoClient:
MongoDB::MongoClient->new( w => 'majority', wtimeout => 1000 );
The "write_concern" method now returns the MongoDB::WriteConcern object generated from "w", "wtimeout"
and "j".
It is inherited by MongoDB::Database, MongoDB::Collection, and MongoDB::GridFS objects unless provided as
an option to the relevant factory methods:
$db = $client->get_database(
"test", { write_concern => { w => 'majority' } }
);
Such "write_concern" arguments may be a MongoDB::WriteConcern object, a hash reference of arguments to
construct one, or a string that represents the "w" mode.
MongoDB::Database and MongoDB::Collection also have "clone" methods that allow easy alteration of a write
concern for a limited scope.
my $coll2 = $coll->clone( write_concern => { w => 1 } );
The "safe" argument is no longer used in the new CRUD API.
Authentication based only on configuration options
Authentication now happens automatically on connection during the "handshake" with any given server based
on the auth_mechanism attribute.
The old "authenticate" method in MongoDB::MongoClient has been removed.
Bulk API
Bulk method names changed to match CRUD API
Method names match the new CRUD API, e.g. "insert_one" instead of "insert" and so one. The legacy names
are deprecated.
Bulk insertion
Insertion via the bulk API will NOT insert an "_id" into the original document if one does not exist.
Previous documentation was not specific whether this was the case or if the "_id" was added to the
document sent to the server.
Bulk write results
The bulk write results class has been renamed to MongoDB::BulkWriteResult. It keeps
"MongoDB::WriteResult" as an empty superclass for some backwards compatibility so that
"$result->isa("MongoDB::WriteResult")" will continue to work as expected.
The attributes have been renamed to be consistent with the new CRUD API. The legacy names are
deprecated, but are available as aliases.
GridFS
The MongoDB::GridFS class now has explicit read preference and write concern attributes inherited from
MongoDB::MongoClient or MongoDB::Database, just like MongoDB::Collection. This means that GridFS
operations now default to an acknowledged write concern, just like collection operations have been doing
since v0.502.0 in 2012.
The use of "safe" is deprecated.
Support for ancient, undocumented positional parameters circa 2010 has been removed.
Low-level functions removed
Low-level driver functions have been removed from the public API.
MongoDB::Connection removed
The "MongoDB::Connection" module was deprecated in v0.502.0 and has been removed.
BSON encoding changes
In the v1 driver, BSON encoding and decoding have been encapsulated into a MongoDB::BSON codec object.
This can be provided at any level, from MongoDB::MongoClient to MongoDB::Collection. If not provided, a
default will be created that behaves similarly to the v0 encoding/decoding functions, except for the
following changes.
$MongoDB::BSON::use_binary removed
Historically, this defaulted to false, which corrupts binary data when round tripping. Retrieving a
binary data element and re-inserting it would have resulted in a field with UTF-8 encoded string of
binary data.
Going forward, binary data will be returned as a MongoDB::BSON::Binary object. A future driver may add
the ability to control decoding to allow alternative representations.
$MongoDB::BSON::use_boolean removed
This global variable never worked. BSON booleans were always deserialized as boolean objects. A future
driver may add the ability to control boolean representation.
$MongoDB::BSON::utf8_flag_on removed
In order to ensure round-tripping of string data, this variable is removed. BSON strings will always be
decoded to Perl character strings. Anything else risks double-encoding a round-trip.
$MongoDB::BSON::looks_like_number and $MongoDB::BSON::char deprecated and re-scoped
In order to allow a future driver to provide more flexible user-customized encoding and decoding, these
global variables are deprecated. If set, they will be examined during "MongoDB::MongoClient->new()" to
set the configuration of a default MongoDB::BSON codec (if one is not provided). Changing them later
will NOT change the behavior of the codec object.
"MongoDB::MongoClient" option "inflate_regexps" removed
Previously, BSON regular expressions decoded to "qr{}" references by default and the
"MongoDB::MongoClient" "inflate_regexps" option was available to decode instead to
MongoDB::BSON::Regexps.
Going forward in the v1.0.0 driver, for safety and consistency with other drivers, BSON regular
expressions always decode to MongoDB::BSON::Regexp objects.
"MongoDB::MongoClient" option "inflate_dbrefs" removed
The "inflate_dbrefs" configuration option has been removed and replaced with a "dbref_callback" option in
MongoDB::BSON.
By default, the "MongoDB::MongoClient" will create a MongoDB::BSON codec that will construct
MongoDB::DBRef objects. This ensures that DBRefs properly round-trip.
"MongoDB::MongoClient" option "dt_type" deprecated and changed to read-only
The "dt_type" option is now only takes effect if "MongoDB::MongoClient" constructs a MongoDB::BSON codec
object. It has been changed to a read-only attribute so that any code that relied on changing "dt_type"
after constructing a "MongoDB::MongoClient" object will fail instead of being silently ignored.
Int32 vs Int64 encoding changes
On 64-bit Perls, integers that fit in 32-bits will be encoded as BSON Int32 (whereas previously these
were always encoded as BSON Int64).
Math::BigInt objects will always be encoded as BSON Int64, which allows users to force 64-bit encoding if
desired.
Added support for Time::Moment
Time::Moment is a much faster replacement for the venerable DateTime module. The BSON codec will
serialize Time::Moment objects correctly and can use that module as an argument for the "dt_type" codec
attribute.
Added support for encoding common JSON boolean classes
Most JSON libraries on CPAN implement their own boolean classes. The following libraries boolean types
will now encode correctly as BSON booleans:
• JSON::XS
• Cpanel::JSON::XS
• JSON::PP
• JSON::Tiny
• Mojo::JSON
DBRef objects
The "fetch" method and related attributes "client", "verify_db", and "verify_coll" have been removed from
MongoDB::DBRef.
Providing a "fetch" method was inconsistent with other MongoDB drivers, which either never provided it,
or have dropped it in the next-generation drivers. It requires a "client" attribute, which tightly
couples BSON decoding to the client model, causing circular reference issues and triggering Perl memory
bugs under threads. Therefore, the v1.0.0 driver no longer support fetching directly from
MongoDB::DBRef; users will need to implement their own methods for dereferencing.
Additionally, the "db" attribute is now optional, consistent with the specification for DBRefs.
Also, all attributes ("ref", "id" and "db") are now read-only, consistent with the move toward immutable
objects throughout the driver.
To support round-tripping DBRefs with additional fields other than $ref, $id and $db, the DBRef class now
has an attribute called "extra". As not all drivers support this feature, using it for new DBRefs is not
recommended.
DEPRECATED METHODS
Deprecated options and methods may be removed in a future release. Their documentation has been removed
to discourage ongoing use. Unless otherwise stated, they will continue to behave as they previously did,
allowing a degree of backwards compatibility until code is updated to the new MongoDB driver API.
MongoDB::Database
• eval – MongoDB 3.0 deprecated the '$eval' command, so this helper method is deprecated as well.
• last_error — Errors are now indicated via exceptions at the time database commands are executed.
MongoDB::Collection
• insert, batch_insert, remove, update, save, query and find_and_modify — A new common driver CRUD API
replaces these legacy methods.
• get_collection — This method implied that collections could be contained inside collection. This
doesn't actually happen so it's confusing to have a Collection be a factory for collections. Users
who want nested namespaces should be explicit and create them off Database objects instead.
• ensure_index, drop_indexes, drop_index, get_index — A new MongoDB::IndexView class is accessible
through the "indexes" method, offering greater consistency in behavior across drivers.
• validate — The return values have changed over different server versions, so this method is risky to
use; it has more use as a one-off tool, which can be accomplished via "run_command".
MongoDB::CommandResult
• result — has been renamed to 'output' for clarity
MongoDB::Cursor
• slave_ok — this modifier method is superseded by the 'read_preference' modifier method
• count — this is superseded by the "MongoDB::Collection#count" in MongoDB::Collection count method.
Previously, this ignored skip/limit unless a true argument was passed, which was a bizarre, non-
intuitive and inconsistent API.
MongoDB::BulkWrite and MongoDB::BulkWriteView
• insert — renamed to 'insert_one' for consistency with CRUD API
• update — renamed to 'update_many' for consistency with CRUD API
• remove — renamed to 'delete_many' for consistency with CRUD API
• remove_one — renamed to 'delete_one' for consistency with CRUD API
AUTHORS
• David Golden <david@mongodb.com>
• Rassi <rassi@mongodb.com>
• Mike Friedman <friedo@friedo.com>
• Kristina Chodorow <k.chodorow@gmail.com>
• Florian Ragwitz <rafl@debian.org>
COPYRIGHT AND LICENSE
This software is Copyright (c) 2020 by MongoDB, Inc.
This is free software, licensed under:
The Apache License, Version 2.0, January 2004
perl v5.34.0 2022-06-30 MongoDB::Upgrading::v1(3pm)