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($string)
Given a string containing a duration (SQL type INTERVAL) representation,
this method will return a new "DateTime::Duration" object.
If given an improperly formatted string, this method may die.
This class provides the following formatting methods.
The output is always in the format mandated by the SQL standard (derived from
ISO 8601), which is parsed by PostgreSQL unambiguously in all DateStyle modes.
- •
- format_datetime($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. Unfortunatly, 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/