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+=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