Provided by: libdatetime-format-pg-perl_0.16014-1_all 
NAME
DateTime::Format::Pg - Parse and format PostgreSQL dates and times
SYNOPSIS
use DateTime::Format::Pg;
my $dt = DateTime::Format::Pg->parse_datetime( '2003-01-16 23:12:01' );
# 2003-01-16 23:12:01
DateTime::Format::Pg->format_datetime($dt);
DESCRIPTION
This module understands the formats used by PostgreSQL for its DATE, TIME, TIMESTAMP, and
INTERVAL data types. It can be used to parse these formats in order to create "DateTime"
or "DateTime::Duration" objects, and it can take a "DateTime" or "DateTime::Duration"
object and produce a string representing it in a format accepted by PostgreSQL.
CONSTRUCTORS
The following methods can be used to create "DateTime::Format::Pg" objects.
• new( name => value, ... )
Creates a new "DateTime::Format::Pg" instance. This is generally not required for
simple operations. If you wish to use a different parsing style from the default then
it is more comfortable to create an object.
my $parser = DateTime::Format::Pg->new()
my $copy = $parser->new( 'european' => 1 );
This method accepts the following options:
• european
If european is set to non-zero, dates are assumed to be in european dd/mm/yyyy
format. The default is to assume US mm/dd/yyyy format (because this is the
default for PostgreSQL).
This option only has an effect if PostgreSQL is set to output dates in the
'PostgreSQL' (DATE only) and 'SQL' (DATE and TIMESTAMP) styles.
Note that you don't have to set this option if the PostgreSQL server has been
set to use the 'ISO' format, which is the default.
• server_tz
This option can be set to a "DateTime::TimeZone" object or a string that
contains a time zone name.
This value must be set to the same value as the PostgreSQL server's time zone
in order to parse TIMESTAMP WITH TIMEZONE values in the 'PostgreSQL', 'SQL',
and 'German' formats correctly.
Note that you don't have to set this option if the PostgreSQL server has been
set to use the 'ISO' format, which is the default.
• clone()
This method is provided for those who prefer to explicitly clone via a method called
"clone()".
my $clone = $original->clone();
If called as a class method it will die.
METHODS
This class provides the following methods. The parse_datetime, parse_duration,
format_datetime, and format_duration methods are general-purpose methods provided for
compatibility with other "DateTime::Format" modules.
The other methods are specific to the corresponding PostgreSQL date/time data types. The
names of these methods are derived from the name of the PostgreSQL data type. (Note:
Prior to PostgreSQL 7.3, the TIMESTAMP type was equivalent to the TIMESTAMP WITH TIME ZONE
type. This data type corresponds to the format/parse_timestamp_with_time_zone method but
not to the format/parse_timestamp method.)
PARSING METHODS
This class provides the following parsing methods.
As a general rule, the parsing methods accept input in any format that the PostgreSQL
server can produce. However, if PostgreSQL's DateStyle is set to 'SQL' or 'PostgreSQL',
dates can only be parsed correctly if the 'european' option is set correctly (i.e. same as
the PostgreSQL server). The same is true for time zones and the 'australian_timezones'
option in all modes but 'ISO'.
The default DateStyle, 'ISO', will always produce unambiguous results and is also parsed
most efficiently by this parser class. I strongly recommend using this setting unless you
have a good reason not to.
• parse_datetime($string,...)
Given a string containing a date and/or time representation, this method will return a
new "DateTime" object.
If the input string does not contain a date, it is set to 1970-01-01. If the input
string does not contain a time, it is set to 00:00:00. If the input string does not
contain a time zone, it is set to the floating time zone.
If given an improperly formatted string, this method may die.
• parse_timestamptz($string,...)
• parse_timestamp_with_time_zone($string,...)
Given a string containing a timestamp (date and time) representation, this method will
return a new "DateTime" object. This method is suitable for the TIMESTAMPTZ (or
TIMESTAMP WITH TIME ZONE) type.
If the input string does not contain a time zone, it is set to the floating time zone.
Please note that PostgreSQL does not actually store a time zone along with the
TIMESTAMP WITH TIME ZONE (or TIMESTAMPTZ) type but will just return a time stamp
converted for the server's local time zone.
If given an improperly formatted string, this method may die.
• parse_timestamp($string,...)
• parse_timestamp_without_time_zone($string,...)
Similar to the functions above, but always returns a "DateTime" object with a floating
time zone. This method is suitable for the TIMESTAMP (or TIMESTAMP WITHOUT TIME ZONE)
type.
If the server does return a time zone, it is ignored.
If given an improperly formatted string, this method may die.
• parse_timetz($string,...)
• parse_time_with_time_zone($string,...)
Given a string containing a time representation, this method will return a new
"DateTime" object. The date is set to 1970-01-01. This method is suitable for the
TIMETZ (or TIME WITH TIME ZONE) type.
If the input string does not contain a time zone, it is set to the floating time zone.
Please note that PostgreSQL stores a numerical offset with its TIME WITH TIME ZONE (or
TIMETZ) type. It does not store a time zone name (such as 'Europe/Rome').
If given an improperly formatted string, this method may die.
• parse_time($string,...)
• parse_time_without_time_zone($string,...)
Similar to the functions above, but always returns an "DateTime" object with a
floating time zone. If the server returns a time zone, it is ignored. This method is
suitable for use with the TIME (or TIME WITHOUT TIME ZONE) type.
This ensures that the resulting "DateTime" object will always have the time zone
expected by your application.
If given an improperly formatted string, this method may die.
• parse_date($string,...)
Given a string containing a date representation, this method will return a new
"DateTime" object. The time is set to 00:00:00 (floating time zone). This method is
suitable for the DATE type.
If given an improperly formatted string, this method may die.
• parse_duration($string)
• parse_interval($string)
Given a string containing a duration (SQL type INTERVAL) representation, this method
will return a new "DateTime::Duration" object.
If given an improperly formatted string, this method may die.
FORMATTING METHODS
This class provides the following formatting methods.
The output is always in the format mandated by the SQL standard (derived from ISO 8601),
which is parsed by PostgreSQL unambiguously in all DateStyle modes.
• format_datetime($datetime,...)
Given a "DateTime" object, this method returns a string appropriate as input for all
date and date/time types of PostgreSQL. It will contain date and time.
If the time zone of the "DateTime" part is floating, the resulting string will contain
no time zone, which will result in the server's time zone being used. Otherwise, the
numerical offset of the time zone is used.
• format_time($datetime,...)
• format_time_without_time_zone($datetime,...)
Given a "DateTime" object, this method returns a string appropriate as input for the
TIME type (also known as TIME WITHOUT TIME ZONE), which will contain the local time of
the "DateTime" object and no time zone.
• format_timetz($datetime)
• format_time_with_time_zone($datetime)
Given a "DateTime" object, this method returns a string appropriate as input for the
TIME WITH TIME ZONE type (also known as TIMETZ), which will contain the local part of
the "DateTime" object and a numerical time zone.
You should not use the TIME WITH TIME ZONE type to store dates with floating time
zones. If the time zone of the "DateTime" part is floating, the resulting string will
contain no time zone, which will result in the server's time zone being used.
• format_date($datetime)
Given a "DateTime" object, this method returns a string appropriate as input for the
DATE type, which will contain the date part of the "DateTime" object.
• format_timestamp($datetime)
• format_timestamp_without_time_zone($datetime)
Given a "DateTime" object, this method returns a string appropriate as input for the
TIMESTAMP type (also known as TIMESTAMP WITHOUT TIME ZONE), which will contain the
local time of the "DateTime" object and no time zone.
• format_timestamptz($datetime)
• format_timestamp_with_time_zone($datetime)
Given a "DateTime" object, this method returns a string appropriate as input for the
TIMESTAMP WITH TIME ZONE type, which will contain the local part of the "DateTime"
object and a numerical time zone.
You should not use the TIMESTAMP WITH TIME ZONE type to store dates with floating time
zones. If the time zone of the "DateTime" part is floating, the resulting string will
contain no time zone, which will result in the server's time zone being used.
• format_duration($du)
• format_interval($du)
Given a "DateTime::Duration" object, this method returns a string appropriate as input
for the INTERVAL type.
LIMITATIONS
Some output formats of PostgreSQL have limitations that can only be passed on by this
class.
As a general rules, none of these limitations apply to the 'ISO' output format. It is
strongly recommended to use this format (and to use PostgreSQL's to_char function when
another output format that's not supposed to be handled by a parser of this class is
desired). 'ISO' is the default but you are advised to explicitly set it at the beginning
of the session by issuing a SET DATESTYLE TO 'ISO'; command in case the server
administrator changes that setting.
When formatting DateTime objects, this class always uses a format that's handled
unambiguously by PostgreSQL.
TIME ZONES
If DateStyle is set to 'PostgreSQL', 'SQL', or 'German', PostgreSQL does not send
numerical time zones for the TIMESTAMPTZ (or TIMESTAMP WITH TIME ZONE) type.
Unfortunately, the time zone names used instead can be ambiguous: For example, 'EST' can
mean -0500, +1000, or +1100.
You must set the 'server_tz' variable to a time zone that is identical to that of the
PostgreSQL server. If the server is set to a different time zone (or the underlying
operating system interprets the time zone differently), the parser will return wrong
times.
You can avoid such problems by setting the server's time zone to UTC using the SET TIME
ZONE 'UTC' command and setting 'server_tz' parameter to 'UTC' (or by using the ISO output
format, of course).
EUROPEAN DATES
For the SQL (for DATE and TIMSTAMP[TZ]) and the PostgreSQL (for DATE) output format, the
server can send dates in both European-style 'dd/mm/yyyy' and in US-style 'mm/dd/yyyy'
format. In order to parse these dates correctly, you have to pass the 'european' option to
the constructor or to the "parse_xxx" routines.
This problem does not occur when using the ISO or German output format (and for PostgreSQL
with TIMESTAMP[TZ] as month names are used then).
INTERVAL ELEMENTS
"DateTime::Duration" stores months, days, minutes and seconds separately. PostgreSQL only
stores months and seconds and disregards the irregular length of days due to DST switching
and the irregular length of minutes due to leap seconds. Therefore, it is not possible to
store "DateTime::Duration" objects as SQL INTERVALs without the loss of some information.
NEGATIVE INTERVALS
In the SQL and German output formats, the server does not send an indication of the sign
with intervals. This means that '1 month ago' and '1 month' are both returned as '1 mon'.
This problem can only be avoided by using the 'ISO' or 'PostgreSQL' output format.
SUPPORT
Support for this module is provided via the datetime@perl.org email list. See
http://lists.perl.org/ for more details.
AUTHOR
Daisuke Maki <daisuke@endeworks.jp>
AUTHOR EMERITUS
Claus A. Faerber <perl@faerber.muc.de>
COPYRIGHT
Copyright (c) 2003 Claus A. Faerber. Copyright (c) 2005-2007 Daisuke Maki
This program is free software; you can redistribute it and/or modify it under the same
terms as Perl itself.
The full text of the license can be found in the LICENSE file included with this module.
SEE ALSO
datetime@perl.org mailing list
http://datetime.perl.org/