NAME
DBD::CSV - DBI driver for CSV files
SYNOPSIS
use DBI;
$dbh = DBI->connect("DBI:CSV:f_dir=/home/joe/csvdb")
or die "Cannot connect: " . $DBI::errstr;
$sth = $dbh->prepare("CREATE TABLE a (id INTEGER, name CHAR(10))")
or die "Cannot prepare: " . $dbh->errstr();
$sth->execute() or die "Cannot execute: " . $sth->errstr();
$sth->finish();
$dbh->disconnect();
# Read a CSV file with ";" as the separator, as exported by
# MS Excel. Note we need to escape the ";", otherwise it
# would be treated as an attribute separator.
$dbh = DBI->connect(qq{DBI:CSV:csv_sep_char=\\;});
$sth = $dbh->prepare("SELECT * FROM info");
# Same example, this time reading "info.csv" as a table:
$dbh = DBI->connect(qq{DBI:CSV:csv_sep_char=\\;});
$dbh->{'csv_tables'}->{'info'} = { 'file' => 'csv'};
$sth = $dbh->prepare("SELECT * FROM info");
WARNING
THIS IS ALPHA SOFTWARE. It is *only* 'Alpha' because the interface (API)
is not finalized. The Alpha status does not reflect code quality or
stability.
DESCRIPTION
The DBD::CSV module is yet another driver for the DBI (Database
independent interface for Perl). This one is based on the SQL "engine"
SQL::Statement and the abstract DBI driver DBD::File and implements
access to so-called CSV files (Comma separated values). Such files are
mostly used for exporting MS Access and MS Excel data.
See the DBI(3) manpage for details on DBI, the SQL::Statement(3) manpage
for details on SQL::Statement and the DBD::File(3) manpage for details
on the base class DBD::File.
Prerequisites
The only system dependent feature that DBD::File uses, is the `flock()'
function. Thus the module should run (in theory) on any system with a
working `flock()', in particular on all Unix machines and on Windows NT.
Under Windows 95 and MacOS the use of `flock()' is disabled, thus the
module should still be usable,
Unlike other DBI drivers, you don't need an external SQL engine or a
running server. All you need are the following Perl modules, available
from any CPAN mirror, for example
ftp://ftp.funet.fi/pub/languages/perl/CPAN/modules/by-module
DBI the DBI (Database independent interface for Perl), version 1.00 or a
later release
SQL::Statement
a simple SQL engine
Text::CSV_XS
this module is used for writing rows to or reading rows from CSV
files.
Installation
Installing this module (and the prerequisites from above) is quite
simple. You just fetch the archive, extract it with
gzip -cd DBD-CSV-0.1000.tar.gz | tar xf -
(this is for Unix users, Windows users would prefer WinZip or something
similar) and then enter the following:
cd DBD-CSV-0.1000
perl Makefile.PL
make
make test
If any tests fail, let me know. Otherwise go on with
make install
Note that you almost definitely need root or administrator permissions.
If you don't have them, read the ExtUtils::MakeMaker man page for
details on installing in your own directories. the ExtUtils::MakeMaker
manpage.
Creating a database handle
Creating a database handle usually implies connecting to a database
server. Thus this command reads
use DBI;
my $dbh = DBI->connect("DBI:CSV:f_dir=$dir");
The directory tells the driver where it should create or open tables
(a.k.a. files). It defaults to the current directory, thus the following
are equivalent:
$dbh = DBI->connect("DBI:CSV:");
$dbh = DBI->connect("DBI:CSV:f_dir=.");
You may set other attributes in the DSN string, separated by semicolons.
Creating and dropping tables
You can create and drop tables with commands like the following:
$dbh->do("CREATE TABLE $table (id INTEGER, name CHAR(64))");
$dbh->do("DROP TABLE $table");
Note that currently only the column names will be stored and no other
data. Thus all other information including column type (INTEGER or
CHAR(x), for example), column attributes (NOT NULL, PRIMARY KEY, ...)
will silently be discarded. This may change in a later release.
A drop just removes the file without any warning.
See the DBI(3) manpage for more details.
Table names cannot be arbitrary, due to restrictions of the SQL syntax.
I recommend that table names are valid SQL identifiers: The first
character is alphabetic, followed by an arbitrary number of alphanumeric
characters. If you want to use other files, the file names must start
with '/', './' or '../' and they must not contain white space.
Inserting, fetching and modifying data
The following examples insert some data in a table and fetch it back:
First all data in the string:
$dbh->do("INSERT INTO $table VALUES (1, "
. $dbh->quote("foobar") . ")");
Note the use of the quote method for escaping the word 'foobar'. Any
string must be escaped, even if it doesn't contain binary data.
Next an example using parameters:
$dbh->do("INSERT INTO $table VALUES (?, ?)", undef,
2, "It's a string!");
Note that you don't need to use the quote method here, this is done
automatically for you. This version is particularly well designed for
loops. Whenever performance is an issue, I recommend using this method.
You might wonder about the `undef'. Don't wonder, just take it as it is.
:-) It's an attribute argument that I have never ever used and will be
parsed to the prepare method as a second argument.
To retrieve data, you can use the following:
my($query) = "SELECT * FROM $table WHERE id > 1 ORDER BY id";
my($sth) = $dbh->prepare($query);
$sth->execute();
while (my $row = $sth->fetchrow_hashref) {
print("Found result row: id = ", $row->{'id'},
", name = ", $row->{'name'});
}
$sth->finish();
Again, column binding works: The same example again.
my($query) = "SELECT * FROM $table WHERE id > 1 ORDER BY id";
my($sth) = $dbh->prepare($query);
$sth->execute();
my($id, $name);
$sth->bind_columns(undef, \$id, \$name);
while ($sth->fetch) {
print("Found result row: id = $id, name = $name\n");
}
$sth->finish();
Of course you can even use input parameters. Here's the same example for
the third time:
my($query) = "SELECT * FROM $table WHERE id = ?";
my($sth) = $dbh->prepare($query);
$sth->bind_columns(undef, \$id, \$name);
for (my($i) = 1; $i <= 2; $i++) {
$sth->execute($id);
if ($sth->fetch) {
print("Found result row: id = $id, name = $name\n");
}
$sth->finish();
}
See the DBI(3) manpage for details on these methods. See the
SQL::Statement(3) manpage for details on the WHERE clause.
Data rows are modified with the UPDATE statement:
$dbh->do("UPDATE $table SET id = 3 WHERE id = 1");
Likewise you use the DELETE statement for removing rows:
$dbh->do("DELETE FROM $table WHERE id > 1");
Error handling
In the above examples we have never cared about return codes. Of course,
this cannot be recommended. Instead we should have written (for
example):
my($query) = "SELECT * FROM $table WHERE id = ?";
my($sth) = $dbh->prepare($query)
or die "prepare: " . $dbh->errstr();
$sth->bind_columns(undef, \$id, \$name)
or die "bind_columns: " . $dbh->errstr();
for (my($i) = 1; $i <= 2; $i++) {
$sth->execute($id)
or die "execute: " . $dbh->errstr();
if ($sth->fetch) {
print("Found result row: id = $id, name = $name\n");
}
}
$sth->finish($id)
or die "finish: " . $dbh->errstr();
Obviously this is tedious. Fortunately we have DBI's *RaiseError*
attribute:
$dbh->{'RaiseError'} = 1;
$@ = '';
eval {
my($query) = "SELECT * FROM $table WHERE id = ?";
my($sth) = $dbh->prepare($query);
$sth->bind_columns(undef, \$id, \$name);
for (my($i) = 1; $i <= 2; $i++) {
$sth->execute($id);
if ($sth->fetch) {
print("Found result row: id = $id, name = $name\n");
}
}
$sth->finish($id);
};
if ($@) { die "SQL database error: $@"; }
This is not only shorter, it even works when using DBI methods within
subroutines.
Metadata
The following attributes are handled by DBI itself and not by DBD::File,
thus they all work as expected:
Active
ActiveKids
CachedKids
CompatMode (Not used)
InactiveDestroy
Kids
PrintError
RaiseError
Warn (Not used)
The following DBI attributes are handled by DBD::File:
AutoCommit
Always on
ChopBlanks
Works
NUM_OF_FIELDS
Valid after `$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 one's, as
DBD::CSV doesn't verify input data. Valid after `$sth->execute';
undef for non-Select statements.
These attributes and methods are not supported:
bind_param_inout
CursorName
LongReadLen
LongTruncOk
In addition to the DBI attributes, you can use the following dbh
attributes:
f_dir This attribute is used for setting the directory where CSV files are
opened. Usually you set it in the dbh, it defaults to the
current directory ("."). However, it is overwritable in the
statement handles.
csv_eol
csv_sep_char
csv_quote_char
csv_escape_char
csv_class
csv_csv The attributes *csv_eol*, *csv_sep_char*, *csv_quote_char* and
*csv_escape_char* are corresponding to the respective attributes
of the Text::CSV_XS object. You want to set these attributes if
you have unusual CSV files like /etc/passwd or MS Excel
generated CSV files with a semicolon as separator. Defaults are
"\015\012", ';', '"' and '"', respectively.
The attributes are used to create an instance of the class
*csv_class*, by default Text::CSV_XS. Alternatively you may pass
an instance as *csv_csv*, the latter takes precedence. Note that
the *binary* attribute *must* be set to a true value in that
case.
Additionally you may overwrite these attributes on a per-table
base in the *csv_tables* attribute.
csv_tables
This hash ref is used for storing table dependent metadata. For
any table it contains an element with the table name as key and
another hash ref with the following attributes:
file The tables file name; defaults to
"$dbh->{f_dir}/$table"
eol
sep_char
quote_char
escape_char
class
csv These correspond to the attributes *csv_eol*,
*csv_sep_char*, *csv_quote_char*, *csv_escape_char*,
*csv_class* and *csv_csv*. The difference is that
they work on a per-table base.
col_names
skip_first_row By default DBD::CSV assumes that column names are stored
in the first row of the CSV file. If this is not the
case, you can supply an array ref of table names
with the *col_names* attribute. In that case the
attribute *skip_first_row* will be set to FALSE.
If you supply an empty array ref, the driver will
read the first row for you, count the number of
columns and create column names like `col0', `col1',
...
Example: Suggest you want to use /etc/passwd as a CSV file. :-) There
simplest way is:
require DBI;
my $dbh = DBI->connect("DBI:CSV:f_dir=/etc;csv_eol=\n;"
. "csv_sep_char=:;csv_quote_char=;"
. "csv_escape_char=");
$dbh->{'csv_tables'}->{'passwd'} = {
'col_names' => ["login", "password", "uid", "gid", "realname",
"directory", "shell"]
};
$sth = $dbh->prepare("SELECT * FROM passwd");
Another possibility where you leave all the defaults as they are and
overwrite them on a per table base:
require DBI;
my $dbh = DBI->connect("DBI:CSV:");
$dbh->{'csv_tables'}->{'passwd'} = {
'eol' => "\n",
'sep_char' => ":",
'quote_char' => undef,
'escape_char' => undef,
'file' => '/etc/passwd',
'col_names' => ["login", "password", "uid", "gid", "realname",
"directory", "shell"]
};
$sth = $dbh->prepare("SELECT * FROM passwd");
Driver private methods
These methods are inherited from DBD::File:
data_sources
The `data_sources' method returns a list of subdirectories of the
current directory in the form "DBI:CSV:directory=$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 $dbh->{'directory'}.
Example:
my($dbh) = DBI->connect("DBI:CSV:directory=/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.
See the section on "Creating and dropping tables" above.
Data restrictions
When inserting and fetching data, you will sometimes be surprised:
DBD::CSV doesn't correctly handle data types, in particular NULLs. If
you insert integers, it might happen, that fetch returns a string. Of
course, a string containing the integer, so that's perhaps not a real
problem. But the following will never work:
$dbh->do("INSERT INTO $table (id, name) VALUES (?, ?)",
undef, "foo bar");
$sth = $dbh->prepare("SELECT * FROM $table WHERE id IS NULL");
$sth->execute();
my($id, $name);
$sth->bind_columns(undef, \$id, \$name);
while ($sth->fetch) {
printf("Found result row: id = %s, name = %s\n",
defined($id) ? $id : "NULL",
defined($name) ? $name : "NULL");
}
$sth->finish();
The row we have just inserted, will never be returned! The reason is
obvious, if you examine the CSV file: The corresponding row looks like
"","foo bar"
In other words, not a NULL is stored, but an empty string. CSV files
don't have a concept of NULL values. Surprisingly the above example
works, if you insert a NULL value for the name! Again, you find the
explanation by examining the CSV file:
""
In other words, DBD::CSV has "emulated" a NULL value by writing a row
with less columns. Of course this works only if the rightmost column is
NULL, the two rightmost columns are NULL, ..., but the leftmost column
will never be NULL!
See the section on "Creating and dropping tables" above for table name
restrictions.
TODO
Extensions of DBD::CSV:
CSV file scanner
Write a simple CSV file scanner that reads a CSV file and attempts
to guess sep_char, quote_char, escape_char and eol automatically.
These are merely restrictions of the DBD::File or SQL::Statement
modules:
Joins
The current version of the module works with single table SELECTs
only, although the basic design of the SQL::Statement module allows
joins and the like.
Table name mapping
Currently it is not possible to use files with names like
`names.csv'. Instead you have to use soft links or rename files. As
an alternative one might use, for example a dbh attribute
'table_map'. It might be a hash ref, the keys being the table names
and the values being the file names.
Column name mapping
Currently the module assumes that column names are stored in the
first row. While this is fine in most cases, there should be a
possibility of setting column names and column number from the
programmer: For example MS Access doesn't export column names by
default.
KNOWN BUGS
* The module is using flock() internally. However, this function is
not available on platforms. Using flock() is disabled on MacOS
and Windows 95: There's no locking at all (perhaps not so
important on these operating systems, as they are for single
users anyways).
AUTHOR AND COPYRIGHT
This module is Copyright (C) 1998 by
Jochen Wiedmann
Am Eisteich 9
72555 Metzingen
Germany
Email: joe@ispsoft.de
Phone: +49 7123 14887
All rights reserved.
You may distribute this module under the terms of either the GNU General
Public License or the Artistic License, as specified in the Perl README
file.
SEE ALSO
the DBI(3) manpage, the Text::CSV_XS(3) manpage, the SQL::Statement(3)
manpage
For help on the use of DBD::CSV, see the DBI users mailing list:
http://www.isc.org/dbi-lists.html
For general information on DBI see
http://www.symbolstone.org/technology/perl/DBI