| DBD::File::Developers - Developers documentation for DBD::File |
DBD::File::Developers - Developers documentation for DBD::File
package DBD::myDriver;
use base qw( DBD::File );
sub driver
{
...
my $drh = $proto->SUPER::driver ($attr);
...
return $drh->{class};
}
sub CLONE { ... }
package DBD::myDriver::dr;
@ISA = qw( DBD::File::dr );
sub data_sources { ... }
...
package DBD::myDriver::db;
@ISA = qw( DBD::File::db );
sub init_valid_attributes { ... }
sub init_default_attributes { ... }
sub set_versions { ... }
sub validate_STORE_attr { my ($dbh, $attrib, $value) = @_; ... }
sub validate_FETCH_attr { my ($dbh, $attrib) = @_; ... }
sub get_myd_versions { ... }
package DBD::myDriver::st;
@ISA = qw( DBD::File::st );
sub FETCH { ... }
sub STORE { ... }
package DBD::myDriver::Statement;
@ISA = qw( DBD::File::Statement );
package DBD::myDriver::Table;
@ISA = qw( DBD::File::Table );
my %reset_on_modify = (
myd_abc => "myd_foo",
myd_mno => "myd_bar",
);
__PACKAGE__->register_reset_on_modify (\%reset_on_modify);
my %compat_map = (
abc => 'foo_abc',
xyz => 'foo_xyz',
);
__PACKAGE__->register_compat_map (\%compat_map);
sub bootstrap_table_meta { ... }
sub init_table_meta { ... }
sub table_meta_attr_changed { ... }
sub open_data { ... }
sub fetch_row { ... }
sub push_row { ... }
sub push_names { ... }
# 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 { ... }
This document describes how DBD developers can write DBD::File based DBI drivers. It supplements the DBI::DBD manpage and the DBI::DBD::SqlEngine::Developers manpage, which you should read first.
Each DBI driver must provide a package global driver method and three
DBI related classes:
DBI->connect ('DBI:DBM:', undef, undef, {})
# invokes package DBD::DBM::dr; @DBD::DBM::dr::ISA = qw( DBD::File::dr );
sub connect ($$;$$$)
{
...
}
Similar for data_sources and disconnect_all.
Pure Perl DBI drivers derived from DBD::File 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.
$dbh). e.g.,
$sth = $dbh->prepare ("select * from foo");
# returns the f_encoding setting for table foo
$dbh->csv_get_meta ("foo", "f_encoding");
DBD::File provides the typical methods required here. Developers who
write DBI drivers based on DBD::File need to override the methods <
set_versions > and init_valid_attributes.
$sth->execute () or die $sth->errstr;
This is the main package containing the routines to initialize
DBD::File based DBI drivers. Primarily the DBD::File::driver
method is invoked, either directly from DBI when the driver is
initialized or from the derived class.
package DBD::DBM;
use base qw( DBD::File );
sub driver
{
my ($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 setup_driver
as DBD::File takes care of it.
The driver package contains the methods DBI calls indirectly via the DBI interface (see DBI Class Methods in the DBI manpage).
DBD::File 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 (DBD::File::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";
This package defines the database methods, which are called via the DBI
database handle $dbh.
Methods provided by DBD::File:
Active attribute. Override
when your driver needs more complicated actions here.
$sth - instance of the DBD:XXX::st. It is neither required nor
recommended to override this method.
$drv_prefix) is added.
The driver prefix is extracted from the attribute name and verified against
$dbh->{$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 $dbh->{
$drv_prefix . "readonly_attrs" } when it exists), a real copy of the
attribute value is returned. So it's not possible to modify
f_valid_attrs from outside of DBD::File::db or a derived class.
$drv_prefix) is added. If the database handle has an attribute
${drv_prefix}_valid_attrs - for attribute names which are not listed in
that hash, this method croaks. If the database handle has an attribute
${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
DBD::File::db::init_valid_attributes.
f_version with the version of DBD::File.
This method is called at the begin of the connect () phase.
When overriding this method, do not forget to invoke the superior one.
DBD::File::db::init_valid_attributes initializes the attributes
f_valid_attrs and f_readonly_attrs.
When overriding this method, do not forget to invoke the superior one, preferably before doing anything else. Compatibility table attribute access must be initialized here to allow DBD::File to instantiate the map tie:
# for DBD::CSV
$dbh->{csv_meta} = "csv_tables";
# for DBD::DBM
$dbh->{dbm_meta} = "dbm_tables";
# for DBD::AnyData
$dbh->{ad_meta} = "ad_tables";
DBD::File::db::init_default_attributes initializes the attributes
f_dir, f_meta, f_meta_map, f_version.
When the derived implementor class provides the attribute to validate
attributes (e.g. $dbh->{dbm_valid_attrs} = {...};) or the attribute
containing the immutable attributes (e.g.
$dbh->{dbm_readonly_attrs} = {...};), the attributes
drv_valid_attrs, drv_readonly_attrs, drv_version and drv_meta
are added (when available) to the list of valid and immutable attributes
(where drv_ is interpreted as the driver prefix).
If drv_meta is set, an attribute with the name in drv_meta is
initialized providing restricted read/write access to the meta data of the
tables using DBD::File::TieTables in the first (table) level and
DBD::File::TieMeta for the meta attribute level. DBD::File::TieTables
uses DBD::DRV::Table::get_table_meta to initialize the second level
tied hash on FETCH/STORE. The DBD::File::TieMeta class uses
DBD::DRV::Table::get_table_meta_attr to FETCH attribute values and
DBD::DRV::Table::set_table_meta_attr to STORE attribute values. This
allows it to map meta attributes for compatibility reasons.
get_file_meta ($dbh, $table, $attr). This method
is called by the injected db handle method ${drv_prefix}get_meta.
While get_file_meta allows $table or $attr to be a list of tables or
attributes to retrieve, get_single_table_meta allows only one table name
and only one attribute name. A table name of '.' (single dot) is
interpreted as the default table and this will retrieve the appropriate
attribute globally from the dbh. This has the same restrictions as
$dbh->{$attrib}.
get_file_meta allows '+' and '*' as wildcards for table names and
$table being a regular expression matching against the table names
(evaluated without the default table). The table name '*' is
all currently known tables, including the default one. The table
name '+' is all table names which conform to
ANSI file name restrictions (/^[_A-Za-z0-9]+$/).
The table meta information is retrieved using the get_table_meta and get_table_meta_attr methods of the table class of the implementation.
set_file_meta ($dbh, $table, $attr, $value). This method is called
by the injected db handle method ${drv_prefix}set_meta.
While set_file_meta allows $table to be a list of tables and $attr
to be a hash of several attributes to set, set_single_table_meta allows
only one table name and only one attribute name/value pair.
The wildcard characters for the table name are the same as for get_file_meta.
The table meta information is updated using the get_table_meta and set_table_meta_attr methods of the table class of the implementation.
clear_file_meta ($dbh, $table). This method is called
by the injected db handle method ${drv_prefix}clear_meta.
Contains the methods to deal with prepared statement handles:
NAME, TYPE, PRECISION
and NULLABLE in case that SQL::Statement is used as SQL execution engine
and a statement is successful prepared. When SQL::Statement has additional
information about a table, those information are returned. Otherwise, the
same defaults as in the DBI::DBD::SqlEngine manpage are used.
This method usually requires extending in a derived implementation. See the DBD::CSV manpage or the DBD::DBM manpage for some example.
Provides data sources and table information on database driver and database handle level.
package DBD::File::TableSource::FileSystem;
sub data_sources ($;$)
{
my ($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 $dbh
attribute or the driver default.
package DBD::File::DataSource::Stream;
@DBD::File::DataSource::Stream::ISA = 'DBI::DBD::SqlEngine::DataSource';
sub complete_table_name
{
my ($self, $meta, $file, $respect_case) = @_;
...
}
Clears all meta attributes identifying a file: f_fqfn, f_fqbn and
f_fqln. The table name is set according to $respect_case and
$meta->{sql_identifier_case} (SQL_IC_LOWER, SQL_IC_UPPER).
package DBD::File::DataSource::Stream;
sub apply_encoding
{
my ($self, $meta, $fn) = @_;
...
}
Applies the encoding from meta information ($meta->{f_encoding})
to the file handled opened in open_data.
package DBD::File::DataSource::Stream;
sub open_data
{
my ($self, $meta, $attrs, $flags) = @_;
...
}
Opens (dup (2)) the file handle provided in $meta->{f_file}.
package DBD::File::DataSource::Stream;
sub can_flock { ... }
Returns whether flock (2) is available or not (avoids retesting in
subclasses).
package DBD::File::DataSource::File;
sub complete_table_name ($$;$)
{
my ($self, $meta, $table, $respect_case) = @_;
...
}
The method complete_table_name tries to map a filename to the associated
table name. It is called with a partially filled meta structure for the
resulting table containing at least the following attributes:
f_ext, f_dir, f_lockfile and sql_identifier_case.
If a file/table map can be found then this method sets the f_fqfn
>>, C<< f_fqbn >>, C<< f_fqln >> and C<< table_name >> attributes in
the meta structure. If a map cannot be found the table name will be
undef.
package DBD::File::DataSource::File;
sub open_data ($)
{
my ($self, $meta, $attrs, $flags) = @_;
...
}
Depending on the attributes set in the table's meta data, the
following steps are performed. Unless f_dontopen is set to a
true value, f_fqfn must contain the full qualified file name
for the table to work on (file2table ensures this). The encoding in
f_encoding is applied if set and the file is opened. If
<f_fqln > (full qualified lock name) is set, this file is opened,
too. Depending on the value in f_lock, the appropriate lock is
set on the opened data file or lock file.
Derives from DBI::SQL::Nano::Statement to provide following method:
file(s) belonging to the
table is handled and parametrized in DBD::File::Table. Unless you intend
to add anything to the following implementation, an empty DBD::XXX::Statement
package satisfies DBD::File.
sub open_table ($$$$$)
{
my ($self, $data, $table, $createMode, $lockMode) = @_;
my $class = ref $self;
$class =~ s/::Statement/::Table/;
my $flags = {
createMode => $createMode,
lockMode => $lockMode,
};
$self->{command} eq "DROP" and $flags->{dropMode} = 1;
return $class->new ($data, { table => $table }, $flags);
} # open_table
Derives from DBI::SQL::Nano::Table and provides physical file access for the table data which are stored in the files.
SUPER method is called at the end
of the overridden method.
It copies the following attributes from the database into the table meta data
f_dir, f_ext, f_encoding, f_lock, f_schema
and f_lockfile and makes them sticky to the table.
This method should be called before you attempt to map between file name and table name to ensure the correct directory, extension etc. are used.
%compat_map, the attribute name is updated from
there.
%compat_map, the attribute name is updated from
there.
If the modified attribute requires to reset a calculated attribute, the
calculated attribute is reset (deleted from meta data structure) and
the initialized flag is removed, too. The decision is made based on
%register_reset_on_modify.
set_table_meta_attr to reset meta attributes when special
attributes are modified. For DBD::File, modifying one of f_file, f_dir,
f_ext or f_lockfile will reset f_fqfn. DBD::DBM extends the
list for dbm_type and dbm_mldbm to reset the value of dbm_tietype.
If your DBD has calculated values in the meta data area, then call
register_reset_on_modify:
my %reset_on_modify = (xxx_foo => "xxx_bar"); __PACKAGE__->register_reset_on_modify (\%reset_on_modify);
get_table_meta_attr and set_table_meta_attr to update the
attribute name to the current favored one:
# from DBD::DBM my %compat_map = (dbm_ext => "f_ext"); __PACKAGE__->register_compat_map (\%compat_map);
Depending on the attributes set in the table's meta data, the
following steps are performed. Unless f_dontopen is set to a
true value, f_fqfn must contain the full qualified file name
for the table to work on (file2table ensures this). The encoding in
f_encoding is applied if set and the file is opened. If
<f_fqln > (full qualified lock name) is set, this file is opened,
too. Depending on the value in f_lock, the appropriate lock is
set on the opened data file or lock file.
After this is done, a derived class might add more steps in an overridden
open_file method.
1. get the table meta data 2. open the data file 3. bless the table data structure using inherited constructor new
It is not recommended to override the constructor of the table class. Find a reasonable place to add you extensions in one of the above four methods.
DROP
command. Discards table meta data after all files belonging to the
table are closed and unlinked.
Overriding this method might be reasonable in very rare cases.
seek is called every time the engine uses dumb algorithms
for iterating over the table content.
UPDATE or DELETE need to truncate the table storage
after the last written row.
You should consult the documentation of SQL::Eval::Table (see
the SQL::Eval manpage) 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.
The module DBD::File is currently maintained by
H.Merijn Brand < h.m.brand at xs4all.nl > and Jens Rehsack < rehsack at googlemail.com >
The original author is Jochen Wiedmann.
Copyright (C) 2010-2013 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.
| DBD::File::Developers - Developers documentation for DBD::File |