phpman > perldoc > DBI::DBD::SqlEngine::Developers(3pm)

NAME
    DBI::DBD::SqlEngine::Developers - Developers documentation for DBI::DBD::SqlEngine

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);

        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 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 { ... }

DESCRIPTION
    This document describes the interface of DBI::DBD::SqlEngine for DBD developers who write
    DBI::DBD::SqlEngine based DBI drivers. It supplements DBI::DBD and DBI::DBD::SqlEngine::HowTo,
    which you should read first.

CLASSES
    Each DBI driver must provide a package global "driver" method and three DBI related classes:

    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 "data_sources ()" and "disconnect_all()".

        Pure Perl DBI drivers derived from DBI::DBD::SqlEngine usually don't need to override any of
        the methods provided through the DBD::XXX::dr package. However if you need additional
        initialization not fitting in "init_valid_attributes()" and "init_default_attributes()" of
        you're ::db class, the connect method might be the final place to be modified.

    DBI::DBD::SqlEngine::db
        Contains the methods which are called through DBI database handles ($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 "set_versions" and
        "init_valid_attributes".

    DBI::DBD::SqlEngine::TieMeta;
        Provides the tie-magic for "$dbh->{$drv_pfx . "_meta"}". Routes "STORE" through
        "$drv->set_sql_engine_meta()" and "FETCH" through "$drv->get_sql_engine_meta()". "DELETE" is
        not supported, you have to execute a "DROP TABLE" statement, where applicable.

    DBI::DBD::SqlEngine::TieTables;
        Provides the tie-magic for tables in "$dbh->{$drv_pfx . "_meta"}". Routes "STORE" though
        "$tblClass->set_table_meta_attr()" and "FETCH" though "$tblClass->get_table_meta_attr()".
        "DELETE" removes an attribute from the *meta object* retrieved by
        "$tblClass->get_table_meta()".

    DBI::DBD::SqlEngine::st
        Contains the methods to deal with prepared statement handles. e.g.,

          $sth->execute () or die $sth->errstr;

    DBI::DBD::SqlEngine::TableSource;
        Base class for 3rd party table sources:

          $dbh->{sql_table_source} = "DBD::Foo::TableSource";

    DBI::DBD::SqlEngine::DataSource;
        Base class for 3rd party data sources:

          $dbh->{sql_data_source} = "DBD::Foo::DataSource";

    DBI::DBD::SqlEngine::Statement;
        Base class for derived drivers statement engine. Implements "open_table".

    DBI::DBD::SqlEngine::Table;
        Contains tailoring between SQL engine's requirements and "DBI::DBD::SqlEngine" magic for
        finding the right tables and storage. Builds bridges between "sql_meta" handling of
        "DBI::DBD::SqlEngine::db", table initialization for SQL engines and *meta object*'s
        attribute management for derived drivers.

  DBI::DBD::SqlEngine
    This is the main package containing the routines to initialize DBI::DBD::SqlEngine based DBI
    drivers. Primarily the "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
    "setup_driver" as DBI::DBD::SqlEngine takes care of it.

  DBI::DBD::SqlEngine::dr
    The driver package contains the methods DBI calls indirectly via the DBI interface (see "DBI
    Class Methods" in DBI).

    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";

   Methods provided by "DBI::DBD::SqlEngine::dr":
    connect
        Supervises the driver bootstrap when calling

          DBI->connect( "dbi:Foo", , , { ... } );

        First it instantiates a new driver using "DBI::_new_dbh". After that, initial bootstrap of
        the newly instantiated driver is done by

          $dbh->func( 0, "init_default_attributes" );

        The first argument (0) signals that this is the very first call to
        "init_default_attributes". Modern drivers understand that and do early stage setup here
        after calling

          package DBD::Foo::db;
          our @DBD::Foo::db::ISA = qw(DBI::DBD::SqlEngine::db);

          sub init_default_attributes
          {
            my ($dbh, $phase) = @_;
            $dbh->SUPER::init_default_attributes($phase);
            ...; # own setup code, maybe separated by phases
          }

        When the $phase argument is passed down until
        "DBI::DBD::SqlEngine::db::init_default_attributes", "connect()" recognizes a *modern* driver
        and initializes the attributes from *DSN* and *$attr* arguments passed via "DBI->connect(
        $dsn, $user, $pass, \%attr )".

        At the end of the attribute initialization after *phase 0*, "connect()" invoked
        "init_default_attributes" again for *phase 1*:

          $dbh->func( 1, "init_default_attributes" );

    data_sources
        Returns a list of *DSN*'s using the "data_sources" method of the class specified in
        "$dbh->{sql_table_source}" or via "\%attr":

          @ary = DBI->data_sources($driver);
          @ary = DBI->data_sources($driver, \%attr);

    disconnect_all
        "DBI::DBD::SqlEngine" doesn't have an overall driver cache, so nothing happens here at all.

  DBI::DBD::SqlEngine::db
    This package defines the database methods, which are called via the DBI database handle $dbh.

   Methods provided by "DBI::DBD::SqlEngine::db":
    ping
        Simply returns the content of the "Active" attribute. Override when your driver needs more
        complicated actions here.

    prepare
        Prepares a new SQL statement to execute. Returns a statement handle, $sth - instance of the
        DBD:XXX::st. It is neither required nor recommended to override this method.

    validate_FETCH_attr
        Called by "FETCH" to allow inherited drivers do their own attribute name validation. Calling
        convention is similar to "FETCH" and the return value is the approved attribute name.

            return $validated_attribute_name;

        In case of validation fails (e.g. accessing private attribute or similar),
        "validate_FETCH_attr" is permitted to throw an exception.

    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 $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
        DBI::DBD::SqlEngine::db or a derived class.

    validate_STORE_attr
        Called by "STORE" to allow inherited drivers do their own attribute name validation. Calling
        convention is similar to "STORE" and the return value is the approved attribute name
        followed by the approved new value.

            return ($validated_attribute_name, $validated_attribute_value);

        In case of validation fails (e.g. accessing private attribute or similar),
        "validate_STORE_attr" is permitted to throw an exception
        ("DBI::DBD::SqlEngine::db::validate_STORE_attr" throws an exception when someone tries to
        assign value other than "SQL_IC_UPPER .. SQL_IC_MIXED" to "$dbh->{sql_identifier_case}" or
        "$dbh->{sql_quoted_identifier_case}").

    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 $drv_prefix) is added. If the database handle has an
        attribute "${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
        "DBI::DBD::SqlEngine::db::init_valid_attributes".

    set_versions
        This method sets the attributes "f_version", "sql_nano_version", "sql_statement_version" and
        (if not prohibited by a restrictive "${prefix}_valid_attrs") "${prefix}_version".

        This method is called at the end of the "connect ()" phase.

        When overriding this method, do not forget to invoke the superior one.

    init_valid_attributes
        This method is called after the database handle is instantiated as the first attribute
        initialization.

        "DBI::DBD::SqlEngine::db::init_valid_attributes" initializes the attributes
        "sql_valid_attrs" and "sql_readonly_attrs".

        When overriding this method, do not forget to invoke the superior one, preferably before
        doing anything else.

    init_default_attributes
        This method is called after the database handle is instantiated to initialize the default
        attributes. It expects one argument: $phase. If $phase is not given, "connect" of
        "DBI::DBD::SqlEngine::dr" expects this is an old-fashioned driver which isn't capable of
        multi-phased initialization.

        "DBI::DBD::SqlEngine::db::init_default_attributes" initializes the attributes
        "sql_identifier_case", "sql_quoted_identifier_case", "sql_handler", "sql_init_order",
        "sql_meta", "sql_engine_version", "sql_nano_version" and "sql_statement_version" when
        SQL::Statement is available.

        It sets "sql_init_order" to the given $phase.

        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" and "drv_version" are added (when available) to the list of valid and
        immutable attributes (where "drv_" is interpreted as the driver prefix).

    get_versions
        This method is called by the code injected into the instantiated driver to provide the user
        callable driver method "${prefix}versions" (e.g. "dbm_versions", "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).

        "get_versions" takes the $dbh as the first argument and optionally a second argument
        containing a table name. The second argument is not evaluated in
        "DBI::DBD::SqlEngine::db::get_versions" itself - but might be in the future.

        If the derived implementor class provides a method named "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.

    sql_parser_object
        Returns a SQL::Parser instance, when "sql_handler" is set to "SQL::Statement". The parser
        instance is stored in "sql_parser_object".

        It is not recommended to override this method.

    disconnect
        Disconnects from a database. All local table information is discarded and the "Active"
        attribute is set to 0.

    type_info_all
        Returns information about all the types supported by DBI::DBD::SqlEngine.

    table_info
        Returns a statement handle which is prepared to deliver information about all known tables.

    list_tables
        Returns a list of all known table names.

    quote
        Quotes a string for use in SQL statements.

    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.

    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.

   Attributes used by "DBI::DBD::SqlEngine::db":
    This section describes attributes which are important to developers of DBI Database Drivers
    derived from "DBI::DBD::SqlEngine".

    sql_init_order
        This attribute contains a hash with priorities as key and an array containing the $dbh
        attributes to be initialized during before/after other attributes.

        "DBI::DBD::SqlEngine" initializes following attributes:

          $dbh->{sql_init_order} = {
               0 => [qw( Profile RaiseError PrintError AutoCommit )],
              90 => [ "sql_meta", $dbh->{$drv_pfx_meta} ? $dbh->{$drv_pfx_meta} : () ]
          }

        The default priority of not listed attribute keys is 50. It is well known that a lot of
        attributes needed to be set before some table settings are initialized. For example, for
        DBD::DBM, when using

          my $dbh = DBI->connect( "dbi:DBM:", undef, undef, {
              f_dir => "/path/to/dbm/databases",
              dbm_type => "BerkeleyDB",
              dbm_mldbm => "JSON", # use MLDBM::Serializer::JSON
              dbm_tables => {
                  quick => {
                      dbm_type => "GDBM_File",
                      dbm_MLDBM => "FreezeThaw"
                  }
              }
          });

        This defines a known table "quick" which uses the GDBM_File backend and FreezeThaw as
        serializer instead of the overall default BerkeleyDB and JSON. But all files containing the
        table data have to be searched in "$dbh->{f_dir}", which requires "$dbh->{f_dir}" must be
        initialized before "$dbh->{sql_meta}->{quick}" is initialized by "bootstrap_table_meta"
        method of "DBI::DBD::SqlEngine::Table" to get "$dbh->{sql_meta}->{quick}->{f_dir}" being
        initialized properly.

    sql_init_phase
        This attribute is only set during the initialization steps of the DBI Database Driver. It
        contains the value of the currently run initialization phase. Currently supported phases are
        *phase 0* and *phase 1*. This attribute is set in "init_default_attributes" and removed in
        "init_done".

    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_table_source
        Names a class which is responsible for delivering *data sources* and *available tables*
        (Database Driver related). *data sources* here refers to "data_sources" in DBI, not
        "sql_data_source".

        See "DBI::DBD::SqlEngine::TableSource" for details.

    sql_data_source
        Name a class which is responsible for handling table resources open and completing table
        names requested via SQL statements.

        See "DBI::DBD::SqlEngine::DataSource" for details.

    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).

  DBI::DBD::SqlEngine::st
    Contains the methods to deal with prepared statement handles:

    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.

    execute
        Executes a previously prepared statement (with placeholders, if any).

    finish
        Finishes a statement handle, discards all buffered results. The prepared statement is not
        discarded so the statement can be executed again.

    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.

    fetchrow_arrayref
        Alias for "fetch".

    FETCH
        Fetches statement handle attributes. Supported attributes (for full overview see "Statement
        Handle Attributes" in DBI) are "NAME", "TYPE", "PRECISION" and "NULLABLE". Each column is
        returned as "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. Note
        that statement attributes are not associated with any table used in this statement.

        This method usually requires extending in a derived implementation. See DBD::CSV or DBD::DBM
        for some example.

    STORE
        Allows storing of statement private attributes. No special handling is currently implemented
        here.

    rows
        Returns the number of rows affected by the last execute. This method might return "undef".

  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.

  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.

  DBI::DBD::SqlEngine::Statement
    Derives from DBI::SQL::Nano::Statement for unified naming when deriving new drivers. No
    additional feature is provided from here.

  DBI::DBD::SqlEngine::Table
    Derives from DBI::SQL::Nano::Table for unified naming when deriving new drivers.

    You should consult the documentation of "SQL::Eval::Table" (see 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.

    bootstrap_table_meta
        Initializes a table meta structure. Can be safely overridden in a derived class, as long as
        the "SUPER" method is called at the end of the overridden method.

        It copies the following attributes from the database into the table meta data
        "$dbh->{ReadOnly}" into "$meta->{readonly}", "sql_identifier_case" and "sql_data_source" 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.

    init_table_meta
        Initializes more attributes of the table meta data - usually more expensive ones (e.g. those
        which require class instantiations) - when the file name and the table name could mapped.

    get_table_meta
        Returns the table meta data. If there are none for the required table, a new one is
        initialized. When after bootstrapping a new *table_meta* and completing the table name a
        mapping can be established between an existing *table_meta* and the new bootstrapped one,
        the already existing is used and a mapping shortcut between the recent used table name and
        the already known table name is hold in "$dbh->{sql_meta_map}". When it fails, nothing is
        returned. On success, the name of the table and the meta data structure is returned.

    get_table_meta_attr
        Returns a single attribute from the table meta data. If the attribute name appears in
        %compat_map, the attribute name is updated from there.

    set_table_meta_attr
        Sets a single attribute in the table meta data. If the attribute name appears in
        %compat_map, the attribute name is updated from there.

    table_meta_attr_changed
        Called when an attribute of the meta data is modified.

        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.

    register_reset_on_modify
        Allows "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 );

    register_compat_map
        Allows "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 );

    open_data
        Called to open the table's data storage. This is silently forwarded to
        "$meta->{sql_data_source}->open_data()".

        After this is done, a derived class might add more steps in an overridden "open_file"
        method.

    new Instantiates the table. This is done in 3 steps:

         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.

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 >

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.