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' => 'info.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.
Supported SQL
The level of SQL support available depends on the version of
SQL::Statement installed. Any version will support *basic*
CREATE, INSERT, DELETE, UPDATE, and SELECT statements. Only
versions of SQL::Statement 1.0 and above support additional
features such as table joins, string functions, etc. See the
documentation of the latest version of SQL::Statement for details.
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:
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 currently maintained by Jeff Zucker <jeff@vpservices.com>.
The original module was written by Jochen Wiedmann.
This module is Copyright (C) 1998 by and Jochen Wiedmann
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