DBI::D...lEngine(3pm) User Contributed Perl Documentation DBI::D...lEngine(3pm)
NAME
DBI::DBD::SqlEngine - Base class for DBI drivers without their own SQL
engine
SYNOPSIS
package DBD::myDriver;
use base qw(DBI::DBD::SqlEngine);
sub driver
{
...
my $drh = $proto->SUPER::driver($attr);
...
return $drh->{class};
}
package DBD::myDriver::dr;
our @ISA = qw(DBI::DBD::SqlEngine::dr);
sub data_sources { ... }
...
package DBD::myDriver::db;
our @ISA = qw(DBI::DBD::SqlEngine::db);
sub init_valid_attributes { ... }
sub init_default_attributes { ... }
sub set_versions { ... }
sub validate_STORE_attr { my ($dbh, $attrib, $value) = @_; ... }
sub validate_FETCH_attr { my ($dbh, $attrib) = @_; ... }
sub get_myd_versions { ... }
sub get_avail_tables { ... }
package DBD::myDriver::st;
our @ISA = qw(DBI::DBD::SqlEngine::st);
sub FETCH { ... }
sub STORE { ... }
package DBD::myDriver::Statement;
our @ISA = qw(DBI::DBD::SqlEngine::Statement);
sub open_table { ... }
package DBD::myDriver::Table;
our @ISA = qw(DBI::DBD::SqlEngine::Table);
sub new { ... }
DESCRIPTION
DBI::DBD::SqlEngine abstracts the usage of SQL engines from the DBD. DBD
authors can concentrate on the data retrieval they want to provide.
It is strongly recommended that you read DBD::File::Developers and
DBD::File::Roadmap, because many of the DBD::File API is provided by
DBI::DBD::SqlEngine.
Currently the API of DBI::DBD::SqlEngine is experimental and will likely
change in the near future to provide the table meta data basics like
DBD::File.
DBI::DBD::SqlEngine expects that any driver in inheritance chain has a
DBI prefix.
Metadata
The following attributes are handled by DBI itself and not by
DBI::DBD::SqlEngine, thus they all work as expected:
Active
ActiveKids
CachedKids
CompatMode (Not used)
InactiveDestroy
AutoInactiveDestroy
Kids
PrintError
RaiseError
Warn (Not used)
The following DBI attributes are handled by DBI::DBD::SqlEngine:
AutoCommit
Always on.
ChopBlanks
Works.
NUM_OF_FIELDS
Valid after "$sth->execute".
NUM_OF_PARAMS
Valid after "$sth->prepare".
NAME
Valid after "$sth->execute"; probably undef for Non-Select statements.
NULLABLE
Not really working, always returns an array ref of ones, as DBD::CSV
does not verify input data. Valid after "$sth->execute"; undef for non-
select statements.
The following DBI attributes and methods are not supported:
bind_param_inout
CursorName
LongReadLen
LongTruncOk
DBI::DBD::SqlEngine specific attributes
In addition to the DBI attributes, you can use the following dbh
attributes:
sql_engine_version
Contains the module version of this driver (readonly)
sql_nano_version
Contains the module version of DBI::SQL::Nano (readonly)
sql_statement_version
Contains the module version of SQL::Statement, if available (readonly)
sql_handler
Contains the SQL Statement engine, either DBI::SQL::Nano or
SQL::Statement (readonly).
sql_parser_object
Contains an instantiated instance of SQL::Parser (readonly). This is
filled when used first time (only when used with SQL::Statement).
sql_sponge_driver
Contains an internally used DBD::Sponge handle (readonly).
sql_valid_attrs
Contains the list of valid attributes for each DBI::DBD::SqlEngine based
driver (readonly).
sql_readonly_attrs
Contains the list of those attributes which are readonly (readonly).
sql_identifier_case
Contains how DBI::DBD::SqlEngine deals with non-quoted SQL identifiers:
* SQL_IC_UPPER (1) means all identifiers are internally converted
into upper-cased pendants
* SQL_IC_LOWER (2) means all identifiers are internally converted
into lower-cased pendants
* SQL_IC_MIXED (4) means all identifiers are taken as they are
These conversions happen if (and only if) no existing identifier
matches. Once existing identifier is used as known.
The SQL statement execution classes doesn't have to care, so don't
expect "sql_identifier_case" affects column names in statements like
SELECT * FROM foo
sql_quoted_identifier_case
Contains how DBI::DBD::SqlEngine deals with quoted SQL identifiers
(readonly). It's fixated to SQL_IC_SENSITIVE (3), which is interpreted
as SQL_IC_MIXED.
sql_flags
Contains additional flags to instantiate an SQL::Parser. Because an
SQL::Parser is instantiated only once, it's recommended to set this flag
before any statement is executed.
sql_dialect
Controls the dialect understood by SQL::Parser. Possible values
(delivery state of SQL::Statement):
* ANSI
* CSV
* AnyData
Defaults to "CSV". Because an SQL::Parser is instantiated only once and
SQL::Parser doesn't allow one to modify the dialect once instantiated,
it's strongly recommended to set this flag before any statement is
executed (best place is connect attribute hash).
sql_engine_in_gofer
This value has a true value in case of this driver is operated via
DBD::Gofer. The impact of being operated via Gofer is a read-only driver
(not read-only databases!), so you cannot modify any attributes later -
neither any table settings. But you won't get an error in cases you
modify table attributes, so please carefully watch
"sql_engine_in_gofer".
sql_meta
Private data area which contains information about the tables this
module handles. Table meta data might not be available until the table
has been accessed for the first time e.g., by issuing a select on it
however it is possible to pre-initialize attributes for each table you
use.
DBI::DBD::SqlEngine recognizes the (public) attributes "col_names",
"table_name", "readonly", "sql_data_source" and "sql_identifier_case".
Be very careful when modifying attributes you do not know, the
consequence might be a destroyed or corrupted table.
While "sql_meta" is a private and readonly attribute (which means, you
cannot modify it's values), derived drivers might provide restricted
write access through another attribute. Well known accessors are
"csv_tables" for DBD::CSV, "ad_tables" for DBD::AnyData and "dbm_tables"
for DBD::DBM.
sql_table_source
Controls the class which will be used for fetching available tables.
See "DBI::DBD::SqlEngine::TableSource" for details.
sql_data_source
Contains the class name to be used for opening tables.
See "DBI::DBD::SqlEngine::DataSource" for details.
Driver private methods
Default DBI methods
data_sources
The "data_sources" method returns a list of subdirectories of the
current directory in the form "dbi:CSV:f_dir=$dirname".
If you want to read the subdirectories of another directory, use
my ($drh) = DBI->install_driver ("CSV");
my (@list) = $drh->data_sources (f_dir => "/usr/local/csv_data");
list_tables
This method returns a list of file names inside $dbh->{f_dir}. Example:
my ($dbh) = DBI->connect ("dbi:CSV:f_dir=/usr/local/csv_data");
my (@list) = $dbh->func ("list_tables");
Note that the list includes all files contained in the directory, even
those that have non-valid table names, from the view of SQL.
Additional methods
The following methods are only available via their documented name when
DBI::DBD::SQlEngine is used directly. Because this is only reasonable
for testing purposes, the real names must be used instead. Those names
can be computed by replacing the "sql_" in the method name with the
driver prefix.
sql_versions
Signature:
sub sql_versions (;$) {
my ($table_name) = @_;
$table_name ||= ".";
...
}
Returns the versions of the driver, including the DBI version, the Perl
version, DBI::PurePerl version (if DBI::PurePerl is active) and the
version of the SQL engine in use.
my $dbh = DBI->connect ("dbi:File:");
my $sql_versions = $dbh->func( "sql_versions" );
print "$sql_versions\n";
__END__
# DBI::DBD::SqlEngine 0.05 using SQL::Statement 1.402
# DBI 1.623
# OS netbsd (6.99.12)
# Perl 5.016002 (x86_64-netbsd-thread-multi)
Called in list context, sql_versions will return an array containing
each line as single entry.
Some drivers might use the optional (table name) argument and modify
version information related to the table (e.g. DBD::DBM provides storage
backend information for the requested table, when it has a table name).
sql_get_meta
Signature:
sub sql_get_meta ($$)
{
my ($table_name, $attrib) = @_;
...
}
Returns the value of a meta attribute set for a specific table, if any.
See sql_meta for the possible attributes.
A table name of "." (single dot) is interpreted as the default table.
This will retrieve the appropriate attribute globally from the dbh.
This has the same restrictions as "$dbh->{$attrib}".
sql_set_meta
Signature:
sub sql_set_meta ($$$)
{
my ($table_name, $attrib, $value) = @_;
...
}
Sets the value of a meta attribute set for a specific table. See
sql_meta for the possible attributes.
A table name of "." (single dot) is interpreted as the default table
which will set the specified attribute globally for the dbh. This has
the same restrictions as "$dbh->{$attrib} = $value".
sql_clear_meta
Signature:
sub sql_clear_meta ($)
{
my ($table_name) = @_;
...
}
Clears the table specific meta information in the private storage of the
dbh.
Extensibility
DBI::DBD::SqlEngine::TableSource
Provides data sources and table information on database driver and
database handle level.
package DBI::DBD::SqlEngine::TableSource;
sub data_sources ($;$)
{
my ( $class, $drh, $attrs ) = @_;
...
}
sub avail_tables
{
my ( $class, $drh ) = @_;
...
}
The "data_sources" method is called when the user invokes any of the
following:
@ary = DBI->data_sources($driver);
@ary = DBI->data_sources($driver, \%attr);
@ary = $dbh->data_sources();
@ary = $dbh->data_sources(\%attr);
The "avail_tables" method is called when the user invokes any of the
following:
@names = $dbh->tables( $catalog, $schema, $table, $type );
$sth = $dbh->table_info( $catalog, $schema, $table, $type );
$sth = $dbh->table_info( $catalog, $schema, $table, $type, \%attr );
$dbh->func( "list_tables" );
Every time where an "\%attr" argument can be specified, this "\%attr"
object's "sql_table_source" attribute is preferred over the $dbh
attribute or the driver default, e.g.
@ary = DBI->data_sources("dbi:CSV:", {
f_dir => "/your/csv/tables",
# note: this class doesn't comes with DBI
sql_table_source => "DBD::File::Archive::Tar::TableSource",
# scan tarballs instead of directories
});
When you're going to implement such a
DBD::File::Archive::Tar::TableSource class, remember to add correct
attributes (including "sql_table_source" and "sql_data_source") to the
returned DSN's.
DBI::DBD::SqlEngine::DataSource
Provides base functionality for dealing with tables. It is primarily
designed for allowing transparent access to files on disk or already
opened (file-)streams (e.g. for DBD::CSV).
Derived classes shall be restricted to similar functionality, too (e.g.
opening streams from an archive, transparently compress/uncompress log
files before parsing them,
package DBI::DBD::SqlEngine::DataSource;
sub complete_table_name ($$;$)
{
my ( $self, $meta, $table, $respect_case ) = @_;
...
}
The method "complete_table_name" is called when first setting up the
meta information for a table:
"SELECT user.id, user.name, user.shell FROM user WHERE ..."
results in opening the table "user". First step of the table open
process is completing the name. Let's imagine you're having a DBD::CSV
handle with following settings:
$dbh->{sql_identifier_case} = SQL_IC_LOWER;
$dbh->{f_ext} = '.lst';
$dbh->{f_dir} = '/data/web/adrmgr';
Those settings will result in looking for files matching
"[Uu][Ss][Ee][Rr](\.lst)?$" in "/data/web/adrmgr/". The scanning of the
directory "/data/web/adrmgr/" and the pattern match check will be done
in "DBD::File::DataSource::File" by the "complete_table_name" method.
If you intend to provide other sources of data streams than files, in
addition to provide an appropriate "complete_table_name" method, a
method to open the resource is required:
package DBI::DBD::SqlEngine::DataSource;
sub open_data ($)
{
my ( $self, $meta, $attrs, $flags ) = @_;
...
}
After the method "open_data" has been run successfully, the table's meta
information are in a state which allows the table's data accessor
methods will be able to fetch/store row information. Implementation
details heavily depends on the table implementation, whereby the most
famous is surely DBD::File::Table.
SQL ENGINES
DBI::DBD::SqlEngine currently supports two SQL engines: SQL::Statement
and DBI::SQL::Nano::Statement_. DBI::SQL::Nano supports a very limited
subset of SQL statements, but it might be faster for some very simple
tasks. SQL::Statement in contrast supports a much larger subset of ANSI
SQL.
To use SQL::Statement, you need at least version 1.401 of SQL::Statement
and the environment variable "DBI_SQL_NANO" must not be set to a true
value.
SUPPORT
You can find documentation for this module with the perldoc command.
perldoc DBI::DBD::SqlEngine
You can also look for information at:
• RT: CPAN's request tracker
<http://rt.cpan.org/NoAuth/Bugs.html?Dist=DBI>
<http://rt.cpan.org/NoAuth/Bugs.html?Dist=SQL-Statement>
• CPAN Ratings
<http://cpanratings.perl.org/d/DBI>
• Search CPAN
<http://search.cpan.org/dist/DBI/>
Where can I go for more help?
For questions about installation or usage, please ask on the
dbi-dev@perl.org mailing list.
If you have a bug report, patch or suggestion, please open a new report
ticket on CPAN, if there is not already one for the issue you want to
report. Of course, you can mail any of the module maintainers, but it is
less likely to be missed if it is reported on RT.
Report tickets should contain a detailed description of the bug or
enhancement request you want to report and at least an easy way to
verify/reproduce the issue and any supplied fix. Patches are always
welcome, too.
ACKNOWLEDGEMENTS
Thanks to Tim Bunce, Martin Evans and H.Merijn Brand for their continued
support while developing DBD::File, DBD::DBM and DBD::AnyData. Their
support, hints and feedback helped to design and implement this module.
AUTHOR
This module is currently maintained by
H.Merijn Brand < h.m.brand at xs4all.nl > and Jens Rehsack < rehsack at
googlemail.com >
The original authors are Jochen Wiedmann and Jeff Zucker.
COPYRIGHT AND LICENSE
Copyright (C) 2009-2020 by H.Merijn Brand & Jens Rehsack
Copyright (C) 2004-2009 by Jeff Zucker
Copyright (C) 1998-2004 by Jochen Wiedmann
All rights reserved.
You may freely distribute and/or modify this module under the terms of
either the GNU General Public License (GPL) or the Artistic License, as
specified in the Perl README file.
SEE ALSO
DBI, DBD::File, DBD::AnyData and DBD::Sys.
perl v5.40.0 2025-02-01 DBI::D...lEngine(3pm)
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