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MongoDB::Upgrading(3) User Contributed Perl DocumentationMongoDB::Upgrading(3)

NAME
       MongoDB::Upgrading - Deprecations and behavior changes from v1 to v2

VERSION
       version v2.2.2

DESCRIPTION
       The v2 driver represents	an evolutionary	rather than revolutionary
       release,	but with enough	differences to justify a major version bump.

       The most	significant change in v2 is a switch away from the embedded
       BSON encoder/decoder to an external library, BSON and an	optional
       optimization addon, BSON::XS.  Many applications	will continue to work
       unmodified, but some may	need changes.

       This document is	intended to help developers update their code to take
       into account API	changes	from the v1 driver to the v2 driver.

RATIONALE
       API Changes are never something to do lightly.  Changes in the v2
       driver were deemed necessary to achieve certain goals, all of which
       echo themes of the v1 driver release:

       o   consistency a particularly with regards to Perl <-> BSON data
	   conversion, the v2 driver provides a	complete, consistently-
	   designed set	of BSON	type wrappers, and significantly improved
	   round-trip capabilities.

       o   server compatibility	a as the MongoDB server	deprecates or removes
	   functionality, the driver must be updated to	match so that users
	   don't develop apps around features that are going away.

       o   portability a the switch to an external library that	has both pure-
	   Perl	and XS optimized versions allows the MongoDB driver to support
	   environments	without	a C compiler available.

INSTALLATION AND DEPENDENCY CHANGES
   Installing v2 over v1
       Because the v2 driver is	pure-Perl capable (see below), its Perl
       installation directory is different.  If	upgrading, you need to be sure
       that the	old version doesn't shadow the new one.

       That's easy with	"cpanm":

	   cpanm --uninst-shadows MongoDB

       For the traditional CPAN	client,	you'll need to configure the
       "make_install_arg" config argument like this:

	   $ perl -MCPAN -e shell
	   cpan> o conf	make_install_arg UNINST=1
	   cpan> o conf	commit
	   cpan> install MongoDB

   BSON	library
       The MongoDB driver uses a newer version of the BSON library.
       Previously, BSON	was already required for BSON::Decimal128, so this is
       a version bump rather than an entirely new dependency.

   Minimum Perl	version
       The MongoDB driver now requires Perl v5.10.1 or later.  This provides
       better pure-Perl	support, several core dependencies, and	many fewer
       bugs involving Unicode and threads.  While threads are discouraged,
       threads under Perl v5.8 were so broken that driver tests	were regularly
       failing.

   Pure-perl capable
       The MongoDB driver can now be installed without needing a compiler.  If
       a compiler is detected, additional XS-based dependencies	will be	added
       to the prerequisites list for improved performance.  You	can also
       specify "PUREPERL_ONLY=1" as a "Makefile.PL" argument to	disable
       compiler	detection.

BSON BEHAVIOR CHANGES
       For detailed information	on handling MongoDB data types in Perl,	see
       MongoDB::DataTypes.  The	following sections provide an overview of
       major changes from past versions.

   MongoDB::BSON is removed
       Code that customized behavior by	instantiating this class will need to
       use BSON	instead.  Options are generally	similar, though	BSON provides
       much more flexibility.

   New type wrapper classes
       The BSON	module provides	a complete set of classes mapping to every
       BSON type.  When	decoding, these	types will be returned for types that
       don't map by default to Perl types.

       Code that uses "ref" to check documents returned	from the database for
       legacy types (e.g.  MongoDB::BSON::Regexp) will need to be updated for
       the new type wrappers.

   Legacy type wrappers
       All the legacy type wrappers have been updated to be subclasses of
       their corresponding BSON	library	equivalents.  For example,
       MongoDB::BSON::Regexp is	a subclass of BSON::Regex.  Most of them are
       empty subclasses	-- the BSON-library versions provide the same API --
       but some	have some additional constructor argument behaviors for
       backwards compatibility.

       The BSON	library	knows how to encode legacy types, so code that uses
       legacy types for	encoding values	should be able to work without
       modification.

       The legacy type wrappers	will be	removed	in a future major version
       release of the driver.

   Default date	type decoding
       The legacy driver defaulted to decoding the BSON	date type as a
       DateTime	object.	 Unfortunately,	that type is very heavy-weight and
       slow to construct; it's a poor choice as	a default as it	inflicts that
       cost whether or not users ultimately need or want objects of that type.

       The previously-deprecated  "dt_type" configuration argument has been
       removed from MongoDB::MongoClient and the default date type of the BSON
       library is BSON::Time, which is extremely lightweight and provides
       convenience methods to convert to various popular time classes.	It
       also works well with Time::HiRes	for recording datetimes	with
       millisecond precision.

       Code that relied	on date	types being DateTime objects will need to
       convert via the "as_datetime" method of BSON::Time.

   More	consistent string/number heuristics
       Depending on their history of use, non-reference	Perl scalars may have
       both string and number representations internally and the MongoDB
       driver wasn't always clear on how it treated them. Moreover, this
       treatment could vary slightly by	Perl version.  The heuristics are now
       standardized as follows:

       o   If the value	has a valid double representation, it will be encoded
	   to BSON as a	double.

       o   Otherwise, if the value has a valid integer interpretation, it will
	   be encoded as either	Int32 or Int64;	the smallest type that the
	   value fits will be used; a value that overflows will	error.

       o   Otherwise, the value	will be	encoded	as a UTF-8 string.

       The BSON	library	provides the "prefer_numeric" attribute	to more
       aggressively coerce number-like strings that don't already have a
       numeric representation into a numeric form.

       This is essentially the same as the legacy heuristic but	some edge
       cases have been made consistent.

   Type	helper functions
       To make it easy to use type wrappers (and to avoid unintentionally
       using a deprecated one),	the BSON::Types	module has a standard set of
       type helper functions:

	   use BSON::Types ':all';

	   $int32    = bson_int32(42);
	   $time     = bson_time(); # now
	   $ordered  = bson_doc( first => "John", last => "Doe );

NON-BSON BEHAVIOR CHANGES
   run_command requires	an ordered document
       The MongoDB database uses the first key of the document provided	to
       "run_command" as	the name of the	command.  Due to Perl's	hash order
       randomization, use of a hash reference with more	than one key as	an
       argument	to "run_command" is not	reliable.  This	restriction is now
       enforced.  The argument must be a BSON::Doc object, a Tie::IxHash
       object, an array	reference with an even number of keys, or a hash
       reference with a	single key.

DEPRECATIONS
   Count method	on collections
       The "count" method is deprecated.

       The reasons for this change are as follows:

       o   The performance and correctness characteristics of the "count"
	   method could	vary widely depending on whether or not	a predicate is
	   used.

       o   The "count" method could be incorrect on sharded clusters during
	   document migration between shards.

       Many users are unaware of these considerations in the use of "count".
       As any change to	"count"	could surprise users with unexpected
       differences in either performance or correctness, the "count" method
       has been	replaced with two new API methods, which more directly convey
       performance and correctness expectations:

       o   "estimated_document_count" takes no predicate; it does not work in
	   transactions; performance is	O(1).

       o   "count_documents" takes a predicate (even if	"empty", meaning count
	   all documents); in can be used with or without transactions;
	   performance is O(N) in the worst case.

       NOTE: When upgrading from the deprecated	"count"	method,	some legacy
       operators are not supported and must be replaced:

	   +-------------+--------------------------------+
	   | Legacy	 | Modern Replacement		  |
	   +=============+================================+
	   | $where	 | $expr (Requires MongoDB 3.6+)  |
	   +-------------+--------------------------------+
	   | $near	 | $geoWithin with $center	  |
	   +-------------+--------------------------------+
	   | $nearSphere | $geoWithin with $centerSphere  |
	   +-------------+--------------------------------+

   Authentication
       The MONGODB-CR authentication mechanism was deprecated in MongoDB
       server 3.6 and removed in MongoDB server	4.0.  The Perl driver is
       deprecating MONGODB-CR, but will	not remove it until it no longer
       supports	older servers.

   Query options
       The following query options are deprecated:

       o   maxScan -- deprecated in MongoDB server 4.0

       o   modifiers --	the old	"$" prefixed modifiers have been replaced with
	   explicit, equivalent	options	for "find"

       o   snapshot -- deprecated in MongoDB server 4.0

   MD5 checksum	for GridFS files
       The "md5" field of GridFS documents is deprecated.  Use of a checksum
       like MD5	has been redundant since MongoDB added write concern and MD5
       itself is no longer considered a	secure digest function.	 A future
       release will remove the use of MD5 entirely.  In	the meantime, users
       can disable MD5 digesting with the "disable_md5"	option in
       MongoDB::GridFSBucket.

       Users who wish to continue storing a digest are encouraged to compute
       their own digest	using a	function of their choice and store it under a
       user-defined key	in the "metadata" field	of the file document.

   Classes
       These classes are superseded by type wrappers from BSON,	as described
       earlier.

       o   MongoDB::BSON::Binary

       o   MongoDB::BSON::Regexp

       o   MongoDB::Code

       o   MongoDB::DBRef

       o   MongoDB::OID

       o   MongoDB::Timestamp

REMOVED	FEATURES
       Features	deprecated in the v1 release have now been removed.
       Additionally, "MongoDB::BSON" has been removed in favor of BSON,	as
       described earlier.

   Configuration options
       o   "dt_type"

       o   "query_timeout"

       o   "sasl"

       o   "sasl_mechanism"

       o   "timeout"

       o   $MongoDB::BSON::char

       o   $MongoDB::BSON::looks_like_number

   Classes
       o   "MongoDB::BSON"

       o   "MongoDB::GridFS"

       o   "MongoDB::GridFS::File"

   Functions/Methods
       o   From	"MongoDB" - "force_double", "force_int"

       o   From	"MongoDB::BulkWrite" and "MongoDB::BulkWriteView" - "insert",
	   "update", "remove", "remove_one"

       o   From	"MongoDB::Collection" -	"insert", "batch_insert", "remove",
	   "update", "save", "query", "find_and_modify", "get_collection",
	   "ensure_index", "drop_indexes", "drop_index", "get_index",
	   "validate"

       o   From	"MongoDB::Database" - "eval", "last_error", "get_gridfs"

       o   From	"MongoDB::CommandResult" - "result"

       o   From	"MongoDB::Cursor" - "slave_okay", "count"

AUTHORS
       o   David Golden	<david@mongodb.com>

       o   Rassi <rassi@mongodb.com>

       o   Mike	Friedman <friedo@friedo.com>

       o   Kristina Chodorow <k.chodorow@gmail.com>

       o   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 v5.32.1			  2020-08-13		 MongoDB::Upgrading(3)

NAME | VERSION | DESCRIPTION | RATIONALE | INSTALLATION AND DEPENDENCY CHANGES | BSON BEHAVIOR CHANGES | NON-BSON BEHAVIOR CHANGES | DEPRECATIONS | REMOVED FEATURES | AUTHORS | COPYRIGHT AND LICENSE

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