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DBD::File(3)                         User Contributed Perl Documentation                        DBD::File(3)



NAME
       DBD::File - Base class for writing file based DBI drivers

SYNOPSIS
       This module is a base class for writing other DBDs.  It is not intended to function as a DBD itself
       (though it is possible).  If you want to access flat files, use DBD::AnyData, or DBD::CSV (both of
       which are subclasses of DBD::File).

DESCRIPTION
       The DBD::File module is not a true DBI driver, but an abstract base class for deriving concrete DBI
       drivers from it. The implication is, that these drivers work with plain files, for example CSV files
       or INI files. The module is based on the SQL::Statement module, a simple SQL engine.

       See DBI for details on DBI, SQL::Statement for details on SQL::Statement and DBD::CSV, DBD::DBM or
       DBD::AnyData for example drivers.

   Metadata
       The following attributes are handled by DBI itself and not by DBD::File, thus they all work as
       expected:

           Active
           ActiveKids
           CachedKids
           CompatMode             (Not used)
           InactiveDestroy
           AutoInactiveDestroy
           Kids
           PrintError
           RaiseError
           Warn                   (Not used)

       The following DBI attributes are handled by DBD::File:

       AutoCommit

       Always on.

       ChopBlanks

       Works.

       NUM_OF_FIELDS

       Valid after "$sth->execute".

       NUM_OF_PARAMS

       Valid after "$sth->prepare".

       NAME

       Valid after "$sth->execute"; undef for Non-Select statements.

       NULLABLE

       Not really working, always returns an array ref of ones, except the affected table has been created
       in this session.  Valid after "$sth->execute"; undef for non-select statements.

       The following DBI attributes and methods are not supported:

       bind_param_inout
       CursorName
       LongReadLen
       LongTruncOk

       DBD::File specific attributes

       In addition to the DBI attributes, you can use the following dbh attributes:

       f_dir

       This attribute is used for setting the directory where the files are opened and it defaults to the
       current directory (.). Usually you set it on the dbh but it may be overridden per table (see f_meta).

       When the value for "f_dir" is a relative path, it is converted into the appropriate absolute path
       name (based on the current working directory) when the dbh attribute is set.

       See "KNOWN BUGS AND LIMITATIONS".

       f_ext

       This attribute is used for setting the file extension. The format is:

         extension{/flag}

       where the /flag is optional and the extension is case-insensitive.  "f_ext" allows you to specify an
       extension which:

       •   makes DBD::File prefer table.extension over table.

       •   makes the table name the filename minus the extension.

           DBI:CSV:f_dir=data;f_ext=.csv

       In the above example and when "f_dir" contains both table.csv and table, DBD::File will open
       table.csv and the table will be named "table". If table.csv does not exist but table does that file
       is opened and the table is also called "table".

       If "f_ext" is not specified and table.csv exists it will be opened and the table will be called
       "table.csv" which is probably not what you want.

       NOTE: even though extensions are case-insensitive, table names are not.

           DBI:CSV:f_dir=data;f_ext=.csv/r

       The "r" flag means the file extension is required and any filename that does not match the extension
       is ignored.

       Usually you set it on the dbh but it may be overridden per table (see f_meta).

       f_schema

       This will set the schema name and defaults to the owner of the directory in which the table file
       resides. You can set "f_schema" to "undef".

           my $dbh = DBI->connect ("dbi:CSV:", "", "", {
               f_schema => undef,
               f_dir    => "data",
               f_ext    => ".csv/r",
               }) or die $DBI::errstr;

       By setting the schema you affect the results from the tables call:

           my @tables = $dbh->tables ();

           # no f_schema
           "merijn".foo
           "merijn".bar

           # f_schema => "dbi"
           "dbi".foo
           "dbi".bar

           # f_schema => undef
           foo
           bar

       Defining "f_schema" to the empty string is equal to setting it to "undef" so the DSN can be
       "dbi:CSV:f_schema=;f_dir=.".

       f_lock

       The "f_lock" attribute is used to set the locking mode on the opened table files. Note that not all
       platforms support locking.  By default, tables are opened with a shared lock for reading, and with an
       exclusive lock for writing. The supported modes are:

         0: No locking at all.

         1: Shared locks will be used.

         2: Exclusive locks will be used.

       But see KNOWN BUGS below.

       f_lockfile

       If you wish to use a lockfile extension other than ".lck", simply specify the "f_lockfile" attribute:

         $dbh = DBI->connect ("dbi:DBM:f_lockfile=.foo");
         $dbh->{f_lockfile} = ".foo";
         $dbh->{f_meta}{qux}{f_lockfile} = ".foo";

       If you wish to disable locking, set the "f_lockfile" to 0.

         $dbh = DBI->connect ("dbi:DBM:f_lockfile=0");
         $dbh->{f_lockfile} = 0;
         $dbh->{f_meta}{qux}{f_lockfile} = 0;

       f_encoding

       With this attribute, you can set the encoding in which the file is opened.  This is implemented using
       "binmode $fh, ":encoding(<f_encoding>)"".

       f_meta

       Private data area which contains information about the tables this module handles. Table meta data
       might not be available until the table has been accessed for the first time e.g., by issuing a select
       on it however it is possible to pre-initialize attributes for each table you use.

       DBD::File recognizes the (public) attributes "f_ext", "f_dir", "f_file", "f_encoding", "f_lock",
       "f_lockfile", "f_schema", "col_names", "table_name" and "sql_identifier_case". Be very careful when
       modifying attributes you do not know, the consequence might be a destroyed or corrupted table.

       "f_file" is an attribute applicable to table meta data only and you will not find a corresponding
       attribute in the dbh. Whilst it may be reasonable to have several tables with the same column names,
       it is not for the same file name. If you need access to the same file using different table names,
       use "SQL::Statement" as the SQL engine and the "AS" keyword:

           SELECT * FROM tbl AS t1, tbl AS t2 WHERE t1.id = t2.id

       "f_file" can be an absolute path name or a relative path name but if it is relative, it is
       interpreted as being relative to the "f_dir" attribute of the table meta data. When "f_file" is set
       DBD::File will use "f_file" as specified and will not attempt to work out an alternative for "f_file"
       using the "table name" and "f_ext" attribute.

       While "f_meta" is a private and readonly attribute (which means, you cannot modify it's values),
       derived drivers might provide restricted write access through another attribute. Well known accessors
       are "csv_tables" for DBD::CSV, "ad_tables" for DBD::AnyData and "dbm_tables" for DBD::DBM.

       Internally private attributes to deal with SQL backends:

       Do not modify any of these private attributes unless you understand the implications of doing so. The
       behavior of DBD::File and derived DBDs might be unpredictable when one or more of those attributes
       are modified.

       sql_nano_version

       Contains the version of loaded DBI::SQL::Nano.

       sql_statement_version

       Contains the version of loaded SQL::Statement.

       sql_handler

       Contains either the text 'SQL::Statement' or 'DBI::SQL::Nano'.

       sql_ram_tables

       Contains optionally temporary tables.

       sql_flags

       Contains optional flags to instantiate the SQL::Parser parsing engine when SQL::Statement is used as
       SQL engine. See SQL::Parser for valid flags.

   Driver private methods
       Default DBI methods

       data_sources

       The "data_sources" method returns a list of subdirectories of the current directory in the form
       "dbi:CSV:f_dir=$dirname".

       If you want to read the subdirectories of another directory, use

           my ($drh)  = DBI->install_driver ("CSV");
           my (@list) = $drh->data_sources (f_dir => "/usr/local/csv_data");

       list_tables

       This method returns a list of file names inside $dbh->{f_dir}.  Example:

           my ($dbh)  = DBI->connect ("dbi:CSV:f_dir=/usr/local/csv_data");
           my (@list) = $dbh->func ("list_tables");

       Note that the list includes all files contained in the directory, even those that have non-valid
       table names, from the view of SQL.

       Additional methods

       The following methods are only available via their documented name when DBD::File is used directly.
       Because this is only reasonable for testing purposes, the real names must be used instead. Those
       names can be computed by replacing the "f_" in the method name with the driver prefix.

       f_versions

       Signature:

           sub f_versions (;$)
           {
               my ($table_name) = @_;
               $table_name ||= ".";
               ...
           }

       Returns the versions of the driver, including the DBI version, the Perl version, DBI::PurePerl
       version (if DBI::PurePerl is active) and the version of the SQL engine in use.

           my $dbh = DBI->connect ("dbi:File:");
           my $f_versions = $dbh->f_versions ();
           print "$f_versions\n";
           __END__
           # DBD::File        0.39 using SQL::Statement 1.28
           # DBI              1.612
           # OS               netbsd (5.99.24)
           # Perl             5.010001 (x86_64-netbsd-thread-multi)

       Called in list context, f_versions will return an array containing each line as single entry.

       Some drivers might use the optional (table name) argument and modify version information related to
       the table (e.g. DBD::DBM provides storage backend information for the requested table, when it has a
       table name).

       f_get_meta

       Signature:

           sub f_get_meta ($$)
           {
               my ($table_name, $attrib) = @_;
               ...
           }

       Returns the value of a meta attribute set for a specific table, if any.  See f_meta for the possible
       attributes.

       A table name of "." (single dot) is interpreted as the default table.  This will retrieve the
       appropriate attribute globally from the dbh.  This has the same restrictions as "$dbh->{$attrib}".

       f_set_meta

       Signature:

           sub f_set_meta ($$$)
           {
               my ($table_name, $attrib, $value) = @_;
               ...
           }

       Sets the value of a meta attribute set for a specific table.  See f_meta for the possible attributes.

       A table name of "." (single dot) is interpreted as the default table which will set the specified
       attribute globally for the dbh.  This has the same restrictions as "$dbh->{$attrib} = $value".

       f_clear_meta

       Signature:

           sub f_clear_meta ($)
           {
               my ($table_name) = @_;
               ...
           }

       Clears the table specific meta information in the private storage of the dbh.

SQL ENGINES
       DBD::File currently supports two SQL engines: SQL::Statement and DBI::SQL::Nano::Statement_.
       DBI::SQL::Nano supports a very limited subset of SQL statements, but it might be faster for some very
       simple tasks. SQL::Statement in contrast supports a much larger subset of ANSI SQL.

       To use SQL::Statement, you need at least version 1.28 of SQL::Statement and the environment variable
       "DBI_SQL_NANO" must not be set to a true value.

KNOWN BUGS AND LIMITATIONS
       •   This module uses flock () internally but flock is not available on all platforms. On MacOS and
           Windows 95 there is no locking at all (perhaps not so important on MacOS and Windows 95, as there
           is only a single user).

       •   The module stores details about the handled tables in a private area of the driver handle ($drh).
           This data area is not shared between different driver instances, so several "DBI->connect ()"
           calls will cause different table instances and private data areas.

           This data area is filled for the first time when a table is accessed, either via an SQL statement
           or via "table_info" and is not destroyed until the table is dropped or the driver handle is
           released.  Manual destruction is possible via f_clear_meta.

           The following attributes are preserved in the data area and will evaluated instead of driver
           globals:

           f_ext
           f_dir
           f_lock
           f_lockfile
           f_encoding
           f_schema
           col_names
           sql_identifier_case

           The following attributes are preserved in the data area only and cannot be set globally.

           f_file

           The following attributes are preserved in the data area only and are computed when initializing
           the data area:

           f_fqfn
           f_fqbn
           f_fqln
           table_name

           For DBD::CSV tables this means, once opened "foo.csv" as table named "foo", another table named
           "foo" accessing the file "foo.txt" cannot be opened.  Accessing "foo" will always access the file
           "foo.csv" in memorized "f_dir", locking "f_lockfile" via memorized "f_lock".

           You can use f_clear_meta or the "f_file" attribute for a specific table to work around this.

       •   When used with SQL::Statement and temporary tables e.g.,

             CREATE TEMP TABLE ...

           the table data processing bypasses DBD::File::Table. No file system calls will be made and there
           are no clashes with existing (file based) tables with the same name. Temporary tables are chosen
           over file tables, but they will not covered by "table_info".

AUTHOR
       This module 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 AND LICENSE
        Copyright (C) 2009-2010 by H.Merijn Brand & Jens Rehsack
        Copyright (C) 2004-2009 by Jeff Zucker
        Copyright (C) 1998-2004 by Jochen Wiedmann

       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.

SEE ALSO
       DBI, DBD::DBM, DBD::CSV, Text::CSV, Text::CSV_XS, SQL::Statement, and DBI::SQL::Nano



perl v5.16.2                                     2012-02-16                                     DBD::File(3)