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DBI::DBD::SqlEngine::DevelopersUser Contributed Perl DocumentatDBI::DBD::SqlEngine::Developers(3)

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 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.

perl v5.16.3				    2013-05-15	       DBI::DBD::SqlEngine::Developers(3)
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