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

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

       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).

       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

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

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

           CompatMode             (Not used)
           Warn                   (Not used)

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


       Always on.




       Valid after "$sth->execute".


       Valid after "$sth->prepare".


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


       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.

       Unsupported DBI attributes and methods





       DBD::File specific attributes

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


       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.

         f_dir => "/data/foo/csv",



       This optional attribute can be set to pass a list of folders to also
       find existing tables. It will not be used to create new files.

         f_dir_search => [ "/data/bar/csv", "/dump/blargh/data" ],


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


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

         f_ext => ".csv/r",

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

       o   makes the table name the filename minus the extension.


       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

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


       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


       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

           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

           # f_schema => "dbi"

           # f_schema => undef

       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=.".


       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.


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

         $dbh = DBI->connect ("");
         $dbh->{f_lockfile} = ".foo";
         $dbh->{dbm_tables}{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->{dbm_tables}{qux}{f_lockfile} = 0;


       With this attribute, you can set the encoding in which the file is
       opened.  This is implemented using "binmode $fh,


       Private data area aliasing "sql_meta" in DBI::DBD::SqlEngine 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", in addition
       to the attributes "sql_meta" in DBI::DBD::SqlEngine already supports.
       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 =

       "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.

       New opportunities for attributes from DBI::DBD::SqlEngine


       "$dbh->{sql_table_source}" can be set to
       DBD::File::TableSource::FileSystem (and is the default setting of
       DBD::File). This provides usual behaviour of previous DBD::File
       releases on

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

         @ary = $dbh->data_sources ();
         @ary = $dbh->data_sources (\%attr);

         @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");


       "$dbh->{sql_data_source}" can be set to either
       DBD::File::DataSource::File, which is default and provides the well
       known behavior of DBD::File releases prior to 0.41, or
       DBD::File::DataSource::Stream, which reuses already opened file-handle
       for operations.

       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


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


       Contains the version of loaded SQL::Statement.


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


       Contains optionally temporary tables.


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

   Driver private methods
       Default DBI methods


       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");

       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



         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 = $dbh->func ("f_versions");
           print "$f_versions\n";
           # DBD::File              0.41 using IO::File (1.16)
           #   DBI::DBD::SqlEngine  0.05 using SQL::Statement 1.406
           # DBI                    1.623
           # OS                     darwin (12.2.1)
           # Perl                   5.017006 (darwin-thread-multi-ld-2level)

       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).

       o   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).

       o   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:


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


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


           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

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

       o   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".

       This module is currently maintained by

       H.Merijn Brand < h.m.brand at > and Jens Rehsack < rehsack at >

       The original author is Jochen Wiedmann.

        Copyright (C) 2009-2013 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.

       DBI, DBD::DBM, DBD::CSV, Text::CSV, Text::CSV_XS, SQL::Statement, and

perl v5.20.0                      2013-07-22                    DBD::File(3pm)

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