Your IP : 172.28.240.42
=head1 NAME
DBI::DBD::SqlEngine::Developers - Developers documentation for DBI::DBD::SqlEngine
=head1 SYNOPSIS
package DBD::myDriver;
use base qw(DBI::DBD::SqlEngine);
sub driver
{
...
my $drh = $proto->SUPER::driver($attr);
...
return $drh->{class};
}
sub CLONE { ... }
package DBD::myDriver::dr;
@ISA = qw(DBI::DBD::SqlEngine::dr);
sub data_sources { ... }
...
package DBD::myDriver::db;
@ISA = qw(DBI::DBD::SqlEngine::db);
sub init_valid_attributes { ... }
sub init_default_attributes { ... }
sub set_versions { ... }
sub validate_STORE_attr { my ($dbh, $attrib, $value) = @_; ... }
sub validate_FETCH_attr { my ($dbh, $attrib) = @_; ... }
sub get_myd_versions { ... }
sub get_avail_tables { ... }
package DBD::myDriver::st;
@ISA = qw(DBI::DBD::SqlEngine::st);
sub FETCH { ... }
sub STORE { ... }
package DBD::myDriver::Statement;
@ISA = qw(DBI::DBD::SqlEngine::Statement);
sub open_table { ... }
package DBD::myDriver::Table;
@ISA = qw(DBI::DBD::SqlEngine::Table);
sub new { ... }
sub fetch_row { ... }
sub push_row { ... }
sub push_names { ... }
sub seek { ... }
sub truncate { ... }
sub drop { ... }
# optimize the SQL engine by add one or more of
sub update_current_row { ... }
# or
sub update_specific_row { ... }
# or
sub update_one_row { ... }
# or
sub insert_new_row { ... }
# or
sub delete_current_row { ... }
# or
sub delete_one_row { ... }
=head1 DESCRIPTION
This document describes the interface of DBI::DBD::SqlEngine for DBD
developers who write DBI::DBD::SqlEngine based DBI drivers. It supplements
L<DBI::DBD> and L<DBI::DBD::SqlEngine::HowTo>, which you should read first.
=head1 CLASSES
Each DBI driver must provide a package global C<< driver >> method and
three DBI related classes:
=over 4
=item DBI::DBD::SqlEngine::dr
Driver package, contains the methods DBI calls indirectly via DBI
interface:
DBI->connect ('DBI:DBM:', undef, undef, {})
# invokes
package DBD::DBM::dr;
@DBD::DBM::dr::ISA = qw(DBI::DBD::SqlEngine::dr);
sub connect ($$;$$$)
{
...
}
Similar for C<< data_sources () >> and C<< disconnect_all() >>.
Pure Perl DBI drivers derived from DBI::DBD::SqlEngine do not usually need to
override any of the methods provided through the DBD::XXX::dr package
however if you need additional initialization in the connect method
you may need to.
=item DBI::DBD::SqlEngine::db
Contains the methods which are called through DBI database handles
(C<< $dbh >>). e.g.,
$sth = $dbh->prepare ("select * from foo");
# returns the f_encoding setting for table foo
$dbh->csv_get_meta ("foo", "f_encoding");
DBI::DBD::SqlEngine provides the typical methods required here. Developers who
write DBI drivers based on DBI::DBD::SqlEngine need to override the methods
C<< set_versions >> and C<< init_valid_attributes >>.
=item DBI::DBD::SqlEngine::st
Contains the methods to deal with prepared statement handles. e.g.,
$sth->execute () or die $sth->errstr;
=back
=head2 DBI::DBD::SqlEngine
This is the main package containing the routines to initialize
DBI::DBD::SqlEngine based DBI drivers. Primarily the
C<< DBI::DBD::SqlEngine::driver >> method is invoked, either directly
from DBI when the driver is initialized or from the derived class.
package DBD::DBM;
use base qw( DBI::DBD::SqlEngine );
sub driver
{
my ( $class, $attr ) = @_;
...
my $drh = $class->SUPER::driver( $attr );
...
return $drh;
}
It is not necessary to implement your own driver method as long as
additional initialization (e.g. installing more private driver
methods) is not required. You do not need to call C<< setup_driver >>
as DBI::DBD::SqlEngine takes care of it.
=head2 DBI::DBD::SqlEngine::dr
The driver package contains the methods DBI calls indirectly via the DBI
interface (see L<DBI/DBI Class Methods>).
DBI::DBD::SqlEngine based DBI drivers usually do not need to implement anything here,
it is enough to do the basic initialization:
package DBD:XXX::dr;
@DBD::XXX::dr::ISA = qw (DBI::DBD::SqlEngine::dr);
$DBD::XXX::dr::imp_data_size = 0;
$DBD::XXX::dr::data_sources_attr = undef;
$DBD::XXX::ATTRIBUTION = "DBD::XXX $DBD::XXX::VERSION by Hans Mustermann";
=head2 DBI::DBD::SqlEngine::db
This package defines the database methods, which are called via the DBI
database handle C<< $dbh >>.
Methods provided by DBI::DBD::SqlEngine:
=over 4
=item ping
Simply returns the content of the C<< Active >> attribute. Override
when your driver needs more complicated actions here.
=item prepare
Prepares a new SQL statement to execute. Returns a statement handle,
C<< $sth >> - instance of the DBD:XXX::st. It is neither required nor
recommended to override this method.
=item FETCH
Fetches an attribute of a DBI database object. Private handle attributes
must have a prefix (this is mandatory). If a requested attribute is
detected as a private attribute without a valid prefix, the driver prefix
(written as C<$drv_prefix>) is added.
The driver prefix is extracted from the attribute name and verified against
C<< $dbh->{ $drv_prefix . "valid_attrs" } >> (when it exists). If the
requested attribute value is not listed as a valid attribute, this method
croaks. If the attribute is valid and readonly (listed in C<< $dbh->{
$drv_prefix . "readonly_attrs" } >> when it exists), a real copy of the
attribute value is returned. So it's not possible to modify
C<f_valid_attrs> from outside of DBI::DBD::SqlEngine::db or a derived class.
=item STORE
Stores a database private attribute. Private handle attributes must have a
prefix (this is mandatory). If a requested attribute is detected as a private
attribute without a valid prefix, the driver prefix (written as
C<$drv_prefix>) is added. If the database handle has an attribute
C<${drv_prefix}_valid_attrs> - for attribute names which are not listed in
that hash, this method croaks. If the database handle has an attribute
C<${drv_prefix}_readonly_attrs>, only attributes which are not listed there
can be stored (once they are initialized). Trying to overwrite such an
immutable attribute forces this method to croak.
An example of a valid attributes list can be found in
C<< DBI::DBD::SqlEngine::db::init_valid_attributes >>.
=item set_versions
This method sets the attributes C<< f_version >>, C<< sql_nano_version >>,
C<< sql_statement_version >> and (if not prohibited by a restrictive
C<< ${prefix}_valid_attrs >>) C<< ${prefix}_version >>.
This method is called at the end of the C<< connect () >> phase.
When overriding this method, do not forget to invoke the superior one.
=item init_valid_attributes
This method is called after the database handle is instantiated as the
first attribute initialization.
C<< DBI::DBD::SqlEngine::db::init_valid_attributes >> initializes the
attributes C<sql_valid_attrs> and C<sql_readonly_attrs>.
When overriding this method, do not forget to invoke the superior one,
preferably before doing anything else.
=item init_default_attributes
This method is called after the database handle is instantiated to
initialize the default attributes.
C<< DBI::DBD::SqlEngine::db::init_default_attributes >> initializes the
attributes C<sql_identifier_case>, C<sql_quoted_identifier_case>,
C<sql_handler>, C<sql_engine_version>, C<sql_nano_version> and
C<sql_statement_version> when L<SQL::Statement> is available.
When the derived implementor class provides the attribute to validate
attributes (e.g. C<< $dbh->{dbm_valid_attrs} = {...}; >>) or the attribute
containing the immutable attributes (e.g. C<< $dbh->{dbm_readonly_attrs}
= {...}; >>), the attributes C<drv_valid_attrs>, C<drv_readonly_attrs> and
C<drv_version> are added (when available) to the list of valid and
immutable attributes (where C<drv_> is interpreted as the driver prefix).
=item get_versions
This method is called by the code injected into the instantiated driver to
provide the user callable driver method C<< ${prefix}versions >> (e.g.
C<< dbm_versions >>, C<< csv_versions >>, ...).
The DBI::DBD::SqlEngine implementation returns all version information known by
DBI::DBD::SqlEngine (e.g. DBI version, Perl version, DBI::DBD::SqlEngine version and
the SQL handler version).
C<get_versions> takes the C<$dbh> as the first argument and optionally a
second argument containing a table name. The second argument is not
evaluated in C<< DBI::DBD::SqlEngine::db::get_versions >> itself - but
might be in the future.
If the derived implementor class provides a method named
C<get_${drv_prefix}versions>, this is invoked and the return value of
it is associated to the derived driver name:
if (my $dgv = $dbh->{ImplementorClass}->can ("get_" . $drv_prefix . "versions") {
(my $derived_driver = $dbh->{ImplementorClass}) =~ s/::db$//;
$versions{$derived_driver} = &$dgv ($dbh, $table);
}
Override it to add more version information about your module, (e.g.
some kind of parser version in case of DBD::CSV, ...), if one line is not
enough room to provide all relevant information.
=item sql_parser_object
Returns a L<SQL::Parser> instance, when C<< sql_handler >> is set to
"SQL::Statement". The parser instance is stored in C<< sql_parser_object >>.
It is not recommended to override this method.
=item disconnect
Disconnects from a database. All local table information is discarded and
the C<< Active >> attribute is set to 0.
=item type_info_all
Returns information about all the types supported by DBI::DBD::SqlEngine.
=item table_info
Returns a statement handle which is prepared to deliver information about
all known tables.
=item list_tables
Returns a list of all known table names.
=item quote
Quotes a string for use in SQL statements.
=item commit
Warns about a useless call (if warnings enabled) and returns.
DBI::DBD::SqlEngine is typically a driver which commits every action instantly when
executed.
=item rollback
Warns about a useless call (if warnings enabled) and returns.
DBI::DBD::SqlEngine is typically a driver which commits every action instantly when
executed.
=back
=head2 DBI::DBD::SqlEngine::st
Contains the methods to deal with prepared statement handles:
=over 4
=item bind_param
Common routine to bind placeholders to a statement for execution. It
is dangerous to override this method without detailed knowledge about
the DBI::DBD::SqlEngine internal storage structure.
=item execute
Executes a previously prepared statement (with placeholders, if any).
=item finish
Finishes a statement handle, discards all buffered results. The prepared
statement is not discarded so the statement can be executed again.
=item fetch
Fetches the next row from the result-set. This method may be rewritten
in a later version and if it's overridden in a derived class, the
derived implementation should not rely on the storage details.
=item fetchrow_arrayref
Alias for C<< fetch >>.
=item FETCH
Fetches statement handle attributes. Supported attributes (for full overview
see L<DBI/Statement Handle Attributes>) are C<NAME>, C<TYPE>, C<PRECISION>
and C<NULLABLE>. Each column is returned as C<NULLABLE> which might be wrong
depending on the derived backend storage. If the statement handle has
private attributes, they can be fetched using this method, too. B<Note> that
statement attributes are not associated with any table used in this statement.
This method usually requires extending in a derived implementation.
See L<DBD::CSV> or L<DBD::DBM> for some example.
=item STORE
Allows storing of statement private attributes. No special handling is
currently implemented here.
=item rows
Returns the number of rows affected by the last execute. This method might
return C<undef>.
=back
=head2 DBI::DBD::SqlEngine::Statement
Derives from DBI::SQL::Nano::Statement for unified naming when deriving
new drivers. No additional feature is provided from here.
=head2 DBI::DBD::SqlEngine::Table
Derives from DBI::SQL::Nano::Table for unified naming when deriving
new drivers. No additional feature is provided from here.
You should consult the documentation of C<< SQL::Eval::Table >> (see
L<SQL::Eval>) to get more information about the abstract methods of the
table's base class you have to override and a description of the table
meta information expected by the SQL engines.
=head1 AUTHOR
The module DBI::DBD::SqlEngine is currently maintained by
H.Merijn Brand < h.m.brand at xs4all.nl > and
Jens Rehsack < rehsack at googlemail.com >
=head1 COPYRIGHT AND LICENSE
Copyright (C) 2010 by H.Merijn Brand & Jens Rehsack
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.
=cut