View file File name : DataTypes.pod Content :# Copyright 2009 - present MongoDB, Inc. # # Licensed under the Apache License, Version 2.0 (the "License"); # you may not use this file except in compliance with the License. # You may obtain a copy of the License at # # http://www.apache.org/licenses/LICENSE-2.0 # # Unless required by applicable law or agreed to in writing, software # distributed under the License is distributed on an "AS IS" BASIS, # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. # See the License for the specific language governing permissions and # limitations under the License. # PODNAME: MongoDB::DataTypes # ABSTRACT: Using MongoDB data types with Perl # vim: set ts=4 sts=4 sw=4 et tw=75: __END__ =pod =encoding UTF-8 =head1 NAME MongoDB::DataTypes - Using MongoDB data types with Perl =head1 VERSION version v2.2.0 =head1 DESCRIPTION MongoDB stores typed data in a data format called BSON (L<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 L<BSON> library (and optional L<BSON::XS> library) for converting between Perl data and the MongoDB BSON format. =head2 Additional information Additional information about MongoDB documents and types may be found in the following MongoDB manual pages: =over 4 =item * L<Documents|https://docs.mongodb.com/manual/core/document/> =item * L<BSON Types|https://docs.mongodb.com/manual/reference/bson-types/> =back =head1 ESSENTIAL CONCEPTS =head2 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. =head2 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 L<BSON> library, such as L<BSON::OID> and L<BSON::Time>. Wrappers for native types are available when necessary to address limitations in Perl's type system. For example, one can use L<BSON::Doc> for a ordered hash or L<BSON::Int64> for a 64-bit integer. The L<BSON> class has attributes that configure how type wrappers are used during encoding and decoding. The L<PERL-BSON Type Mapping|BSON/PERL-BSON-TYPE-MAPPING> documentation has a detailed table of all BSON type conversions. =head2 String/number type conversion heuristics Perl's scalar values can have several underlying, internal representations such as double, integer, or string (see L<perlguts>). When encoding to BSON, the default behavior is as follows: =over 4 =item * If the value has a valid double representation, it will be encoded to BSON as a double. =item * 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. =item * Otherwise, the value will be encoded as a UTF-8 string. =back The L<BSON> library provides the C<prefer_numeric> attribute to more aggressively coerce number-like strings that don't already have a numeric representation into a numeric form. =head2 Order sometimes matters a lot When writing a query document, the order of B<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 L</Documents> section below for specific guidance. =head1 THE BSON::TYPES LIBRARY L<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 L<BSON::Types> helper functions are loaded. =head1 NOTES ON SPECIFIC TYPES =head2 Arrays BSON arrays encode and decode via Perl array references. =head2 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 L<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 L<Tie::IxHash> for a more-interactive ordered document, but at the expense of tied-object overhead. The L<BSON> encoder has an C<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. =head2 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 L<wrap_numbers|BSON/wrap_numbers> attribute to always decode to a BSON type wrapper class with numeric overloading. =head3 32-bit Platforms On a 32-bit platform, the L<BSON> library treats L<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 L<Math::BigInt> objects. =head3 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 =head3 Long doubles On a perl compiled with long-double support, floating point number precision will be lost when sending data to MongoDB. =head3 Decimal128 MongoDB 3.4 adds support for the IEEE 754 Decimal128 type. The L<BSON::Decimal128> class is used as a proxy for these values for both inserting and querying documents. Be sure to use B<strings> when constructing Decimal128 objects. $item = { name => "widget", price => bson_decimal128("4.99"), # 4.99 as a string currency => "USD", }; $coll->insert_one($item); =head2 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 L</Binary Data>, below). =head2 Booleans Boolean values are emulated using the L<boolean> package via the C<boolean::true> and C<boolean::false> functions. Using L<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 L<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 C<true> and C<false>, but some commands require L<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: =over 4 =item * L<JSON::XS> =item * L<JSON::PP> =item * L<Cpanel::JSON::XS> =item * L<Mojo::JSON> =item * L<JSON::Tiny> =back =head2 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 C<_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 L<BSON::OID> class is the type wrapper for object IDs. To create a unique id: $oid = bson_oid(); To create a L<BSON::OID> from an existing 24-character hexadecimal string: $oid = bson_oid("123456789012345678901234"); =head2 Regular Expressions Use C<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 L<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. B<NOTE>: only the following flags are supported: "imsxlu". You can also save and retrieve regular expressions themselves, but regular expressions will be retrieved as L<BSON::Regex> objects for safety (these will round-trip correctly). From that object, you can attempt to compile a reference to a C<qr{}> using the C<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"; } B<SECURITY NOTE>: A regular expression can evaluate arbitrary code if C<use re 'eval'> is in scope. You are strongly advised never to use untrusted input as a regular expression. =head2 Dates BSON has a datetime type representing signed Int64 milliseconds relative to the Unix epoch. As of MongoDB v2.0.0, the lightweight L<BSON::Time> wrapper is now the default wrapper for datetime data. The C<bson_time()> helper function uses fractional epoch seconds, for better integration with the L<Time::HiRes> module: use Time::HiRes 'time'; $later = bson_time( time() + 60 ); For convenience, The default value for the helper is C<Time::HiRes::time>: $now = bson_time(); L<BSON::Time> has methods for inflating into various popular Perl date classes, including L<DateTime>, L<Time::Moment> and L<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, L<DateTime::Tiny> has no time zone or sub-second precision. =head2 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 L<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 L<BSON::Bytes> wrapper: # non-utf8 string $bytes = "\xFF\xFE\xFF"; $collection->insert_one({"photo" => bson_bytes($bytes)}); Binary data will be decoded into a L<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}); =head2 MinKey and MaxKey L<BSON::MinKey> is "less than" any other value of any type. This can be useful for always returning certain documents first. L<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(); =head1 AUTHORS =over 4 =item * David Golden <david@mongodb.com> =item * Rassi <rassi@mongodb.com> =item * Mike Friedman <friedo@friedo.com> =item * Kristina Chodorow <k.chodorow@gmail.com> =item * Florian Ragwitz <rafl@debian.org> =back =head1 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 =cut