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