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MongoDB::DataTypes(3pm) User Contributed Perl Documentation MongoDB::DataTypes(3pm)
NAME
MongoDB::DataTypes - Using MongoDB data types with Perl
VERSION
version v2.2.0
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:
o Documents <https://docs.mongodb.com/manual/core/document/>
o 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:
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.
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:
o JSON::XS
o JSON::PP
o Cpanel::JSON::XS
o Mojo::JSON
o 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
o David Golden <david AT mongodb.com>
o Rassi <rassi AT mongodb.com>
o Mike Friedman <friedo AT friedo.com>
o Kristina Chodorow <k.chodorow AT gmail.com>
o Florian Ragwitz <rafl AT debian.org>
COPYRIGHT AND LICENSE
This software is Copyright (c) 2019 by MongoDB, Inc.
This is free software, licensed under:
The Apache License, Version 2.0, January 2004
perl v5.30.0 2019-10-10 MongoDB::DataTypes(3pm)
Generated by $Id: phpMan.php,v 4.55 2007/09/05 04:42:51 chedong Exp $ Author: Che Dong
On Apache
Under GNU General Public License
2024-04-26 10:24 @18.117.158.47 CrawledBy Mozilla/5.0 AppleWebKit/537.36 (KHTML, like Gecko; compatible; ClaudeBot/1.0; +claudebot@anthropic.com)