Provided by: libmongodb-perl_2.2.2-1_all 
NAME
MongoDB::DataTypes - Using MongoDB data types with Perl
VERSION
version v2.2.2
DESCRIPTION
MongoDB stores typed data in a data format called BSON (<http://bsonspec.org/>). This document describes
how to work with BSON data types in the MongoDB Perl driver.
As of the MongoDB Perl driver v2.0.0, the driver relies on the external BSON library (and optional
BSON::XS library) for converting between Perl data and the MongoDB BSON format.
Additional information
Additional information about MongoDB documents and types may be found in the following MongoDB manual
pages:
• Documents <https://docs.mongodb.com/manual/core/document/>
• BSON Types <https://docs.mongodb.com/manual/reference/bson-types/>
ESSENTIAL CONCEPTS
MongoDB records are ordered documents
A MongoDB record (i.e. "row") is a BSON document -- a list of key-value pairs, like a Perl hash except
that the keys in a BSON document are ordered. Keys are always strings. Values can be any of 20+ BSON
types.
Queries and update specifications are also expressed as documents.
Type wrapper classes provide non-native and disambiguated types
In order to represent BSON types that don't natively exist in Perl, we use type wrapper classes from the
BSON library, such as BSON::OID and BSON::Time.
Wrappers for native types are available when necessary to address limitations in Perl's type system. For
example, one can use BSON::Doc for a ordered hash or BSON::Int64 for a 64-bit integer.
The BSON class has attributes that configure how type wrappers are used during encoding and decoding.
The PERL-BSON Type Mapping documentation has a detailed table of all BSON type conversions.
String/number type conversion heuristics
Perl's scalar values can have several underlying, internal representations such as double, integer, or
string (see perlguts). When encoding to BSON, the default behavior is as follows:
• If the value has a valid double representation, it will be encoded to BSON as a double.
• 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.
• 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.
Order sometimes matters a lot
When writing a query document, the order of top level keys doesn't matter, but the order of keys in any
embedded documents does matter.
$coll->insert_one({
name => { first => "John", last => "Doe" },
age => 42,
color => "blue",
});
# Order doesn't matter here
$coll->find( { age => 42, color => "blue" } ); # MATCH
$coll->find( { color => "blue", age => 42 } ); # MATCH
# Order *does* matter here
$coll->find(
{ name => { first => "John", last => "Doe" } } # MATCH
);
$coll->find(
{ name => { last => "Doe", first => "John" } } # NO MATCH
);
When specifying a sort order or the order of keys for an index, order matters whenever there is more than
one key.
Because of Perl's hash order randomization, be very careful using native hashes with MongoDB. See the
"Documents" section below for specific guidance.
THE BSON::TYPES LIBRARY
BSON::Types is a library with helper subroutines to easily create BSON type wrappers. Use of this
library is highly recommended.
use BSON::Types ':all';
$int64 = bson_int64(42); # force encoding more bits
$decimal = bson_decimal("24.01"); # Decimal128 type
$time = bson_time(); # now
Examples in the rest of this document assume that all BSON::Types helper functions are loaded.
NOTES ON SPECIFIC TYPES
Arrays
BSON arrays encode and decode via Perl array references.
Documents
Because Perl's hashes guarantee key-order randomness, using hash references as documents will lead to
BSON documents with a different key order. For top-level keys, this shouldn't cause problems, but it may
cause problems for embedded documents when querying, sorting or indexing on the embedded document.
For sending data to the server, the BSON::Doc class provides a very lightweight wrapper around ordered
key-value pairs, but it's opaque.
$doc = bson_doc( name => "Larry", color => "purple" );
You can also use Tie::IxHash for a more-interactive ordered document, but at the expense of tied-object
overhead.
The BSON encoder has an "ordered" attribute that, if enabled, returns all documents as order-preserving
tied hashes. This is slow, but is the only way to ensure that documents can roundtrip preserving key
order.
Numbers
By default, the BSON decoder decodes doubles and integers into a Perl-native form. To maximize fidelity
during a roundtrip, the decoder supports the wrap_numbers attribute to always decode to a BSON type
wrapper class with numeric overloading.
32-bit Platforms
On a 32-bit platform, the BSON library treats Math::BigInt as the "native" type for integers outside the
(signed) 32-bit range. Values that are encoded as 64-bit integers will be decoded as Math::BigInt
objects.
64-bit Platforms
On a 64-bit platform, (signed) Int64 values are supported, but, by default, numbers will be stored in the
smallest BSON size needed. To force a 64-bit representation for numbers in the signed 32-bit range, use
a type wrapper:
$int64 = bson_int64(0); # 64 bits of 0
Long doubles
On a perl compiled with long-double support, floating point number precision will be lost when sending
data to MongoDB.
Decimal128
MongoDB 3.4 adds support for the IEEE 754 Decimal128 type. The BSON::Decimal128 class is used as a proxy
for these values for both inserting and querying documents. Be sure to use strings when constructing
Decimal128 objects.
$item = {
name => "widget",
price => bson_decimal128("4.99"), # 4.99 as a string
currency => "USD",
};
$coll->insert_one($item);
Strings
String values are expected to be character-data (not bytes). They are encoded as UTF-8 before being sent
to the database and decoded from UTF-8 when received. If a string can't be decoded, an error will be
thrown.
To save or query arbitrary, non-UTF8 bytes, use a binary type wrapper (see "Binary Data", below).
Booleans
Boolean values are emulated using the boolean package via the "boolean::true" and "boolean::false"
functions. Using boolean objects in documents will ensure the documents have the BSON boolean type in
the database. Likewise, BSON boolean types in the database will be returned as boolean objects.
An example of inserting boolean values:
use boolean;
$collection->insert_one({"okay" => true, "name" => "fred"});
An example of using boolean values for query operators (only returns documents where the name field
exists):
$cursor = $collection->find({"name" => {'$exists' => true}});
Often, you can just use 1 or 0 in query operations instead of "true" and "false", but some commands
require boolean objects and the database will return an error if integers 1 or 0 are used.
Boolean objects from the following JSON libraries will also be encoded correctly in the database:
• JSON::XS
• JSON::PP
• Cpanel::JSON::XS
• Mojo::JSON
• JSON::Tiny
Object IDs
The BSON object ID type (aka "OID") is a 12 byte identifier that ensures uniqueness by mixing a timestamp
and counter with host and process-specific bytes.
All MongoDB documents have an "_id" field as a unique identifier. This field does not have to be an
object ID, but if the field does not exist, an object ID is created automatically for it when the
document is inserted into the database.
The BSON::OID class is the type wrapper for object IDs.
To create a unique id:
$oid = bson_oid();
To create a BSON::OID from an existing 24-character hexadecimal string:
$oid = bson_oid("123456789012345678901234");
Regular Expressions
Use "qr/.../" to use a regular expression in a query, but be sure to limit your regular expression to
syntax and features supported by PCRE, which are not fully compatible with Perl
<https://en.wikipedia.org/wiki/Perl_Compatible_Regular_Expressions#Differences_from_Perl>.
$cursor = $collection->find({"name" => qr/[Jj]oh?n/});
Regular expressions will match strings saved in the database.
NOTE: only the following flags are supported: "imsxlu".
You can also save and retrieve regular expressions themselves, but regular expressions will be retrieved
as BSON::Regex objects for safety (these will round-trip correctly).
From that object, you can attempt to compile a reference to a "qr{}" using the "try_compile" method.
However, due to PCRE differences, this could fail to compile or could have different match behavior than
intended.
$collection->insert_one({"regex" => qr/foo/i});
$obj = $collection->find_one;
if ("FOO" =~ $obj->{regex}->try_compile) { # matches
print "hooray\n";
}
SECURITY NOTE: A regular expression can evaluate arbitrary code if "use re 'eval'" is in scope. You are
strongly advised never to use untrusted input as a regular expression.
Dates
BSON has a datetime type representing signed Int64 milliseconds relative to the Unix epoch. As of
MongoDB v2.0.0, the lightweight BSON::Time wrapper is now the default wrapper for datetime data.
The "bson_time()" helper function uses fractional epoch seconds, for better integration with the
Time::HiRes module:
use Time::HiRes 'time';
$later = bson_time( time() + 60 );
For convenience, The default value for the helper is "Time::HiRes::time":
$now = bson_time();
BSON::Time has methods for inflating into various popular Perl date classes, including DateTime,
Time::Moment and DateTime::Tiny. The BSON encoder can also encode objects of these types, with
limitations on precision and timezone based on the underlying class. For example, DateTime::Tiny has no
time zone or sub-second precision.
Binary Data
By default, all database strings are UTF-8. To store images, binaries, and other non-UTF-8 data, one can
use the BSON binary data type via the BSON::Bytes wrapper.
The BSON binary type includes the notion of a "subtype" attribute, which can be any integer between 0 and
255. The meaning of subtypes from 0 to 127 are reserved for definition by MongoDB; values 128 to 255 are
user-defined. Binary data values will only match in a MongoDB query if both the binary bytes and the
subtypes are the same. The default subtype is 0 (a.k.a. "generic binary data") and generally should not
be modified.
To roundtrip binary data, use the BSON::Bytes wrapper:
# non-utf8 string
$bytes = "\xFF\xFE\xFF";
$collection->insert_one({"photo" => bson_bytes($bytes)});
Binary data will be decoded into a BSON::Bytes object. It stringifies as the underlying bytes for
convenience.
One can also store binary data by using a string reference.
$collection->insert_one({"photo" => \$bytes});
MinKey and MaxKey
BSON::MinKey is "less than" any other value of any type. This can be useful for always returning certain
documents first.
BSON::MaxKey is "greater than" any other value of any type. This can be useful for always returning
certain documents last.
There is a helper function for each:
$min = bson_minkey();
$max = bson_maxkey();
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