DBD::File(3pm) User Contributed Perl Documentation DBD::File(3pm)
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.
Unsupported DBI attributes and methods
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.
f_dir => "/data/foo/csv",
See "KNOWN BUGS AND LIMITATIONS".
f_dir_search
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" ],
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:
f_ext => ".csv/r",
• 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->{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;
f_encoding
With this attribute, you can set the encoding in which the file is
opened. This is implemented using "binmode $fh,
":encoding(<f_encoding>)"".
f_meta
Private data area aliasing "sql_meta" in DBI::DBD::SqlEngine which
contains information about the tables this module handles. Table meta
data might not be available until the table has been accessed for the
first time e.g., by issuing a select on it however it is possible to
pre-initialize attributes for each table you use.
DBD::File recognizes the (public) attributes "f_ext", "f_dir",
"f_file", "f_encoding", "f_lock", "f_lockfile", "f_schema", in addition
to the attributes "sql_meta" in DBI::DBD::SqlEngine already supports.
Be very careful when modifying attributes you do not know, the
consequence might be a destroyed or corrupted table.
"f_file" is an attribute applicable to table meta data only and you
will not find a corresponding attribute in the dbh. Whilst it may be
reasonable to have several tables with the same column names, it is not
for the same file name. If you need access to the same file using
different table names, use "SQL::Statement" as the SQL engine and the
"AS" keyword:
SELECT * FROM tbl AS t1, tbl AS t2 WHERE t1.id = t2.id
"f_file" can be an absolute path name or a relative path name but if it
is relative, it is interpreted as being relative to the "f_dir"
attribute of the table meta data. When "f_file" is set DBD::File will
use "f_file" as specified and will not attempt to work out an
alternative for "f_file" using the "table name" and "f_ext" attribute.
While "f_meta" is a private and readonly attribute (which means, you
cannot modify it's values), derived drivers might provide restricted
write access through another attribute. Well known accessors are
"csv_tables" for DBD::CSV, "ad_tables" for DBD::AnyData and
"dbm_tables" for DBD::DBM.
New opportunities for attributes from DBI::DBD::SqlEngine
sql_table_source
"$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);
$dbh->func ("list_tables");
sql_data_source
"$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
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) = $drh->data_sources (f_dir => "/usr/local/csv_data");
Additional methods
The following methods are only available via their documented name when
DBD::File is used directly. Because this is only reasonable for testing
purposes, the real names must be used instead. Those names can be
computed by replacing the "f_" in the method name with the driver
prefix.
f_versions
Signature:
sub f_versions (;$)
{
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 = $dbh->func ("f_versions");
print "$f_versions\n";
__END__
# 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).
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_dir_search
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) 2009-2013 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.
SEE ALSO
DBI, DBD::DBM, DBD::CSV, Text::CSV, Text::CSV_XS, SQL::Statement, and
DBI::SQL::Nano
perl v5.38.2 2024-04-01 DBD::File(3pm)
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