dbd::csv(3)

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 DBI(3) for details on DBI, SQL::Statement(3) for details on SQL::Statement and DBD::File(3) 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 partic
ular 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 ExtU tils::MakeMaker man page for details on installing in your own directories. ExtUtils::MakeMaker.: The level of SQL support available depends on the ver; sion of
SQL::Statement installed. Any version will support *ba; sic*
CREATE, INSERT, DELETE, UPDATE, and SELECT statements.; Only
versions of SQL::Statement 1.0 and above support addi; tional
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=.");
(I was told, that VMS requires: $dbh = DBI->connect("DBI:CSV:f_dir=");
for whatever reasons.)
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 fol lowing:: $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 DBI(3) 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, fol lowed 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 $table VALUES (?, ?)", undef,
2, "It's a string!");
Note that you don't need to use the quote method here, this is done automatically for you. This version is par ticularly well designed for loops. Whenever performance is an issue, I recommend using this method.
You might wonder about the "undef". Don't wonder, just take it as it is. :-) It's an attribute argument that I have never ever used and will be parsed to the prepare method as a second argument.
To retrieve data, you can use the following:: my($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);
$sth->bind_columns(undef, d, ame);
while ($sth->fetch) {
print("Found result row: id = $id, name = $name0);

}
$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);
$sth->bind_columns(undef, d, ame);
for (my($i) = 1; $i <= 2; $i++) {
$sth->execute($id);
if ($sth->fetch) {
print("Found result row: id = $id, name =

$name0);

}
$sth->finish();

}; See DBI(3) for details on these methods. See SQL::State_ ment(3) 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, d, ame)

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 =

$name0);

}

}
$sth->finish($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);
$sth->bind_columns(undef, d, ame);
for (my($i) = 1; $i <= 2; $i++) {
$sth->execute($id);
if ($sth->fetch) {
print("Found result row: id = $id, name =

$name0);

}

}
$sth->finish($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 state
ments.
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 state
ment 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 correspond ing 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 " 15 12",
';', '"' 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 col
umn 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=0"
.

"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' => "0,
'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 subdirec
tories 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:directo

ry=/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 "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 hap pen, that fetch returns a string. Of course, a string con taining 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);
$sth->bind_columns(undef, d, ame);
while ($sth->fetch) {
printf("Found result row: id = %s, name = %s0,
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 corre
sponding 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. Surpris
ingly 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 "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 val
ues 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 exam
ple 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 impor
tant 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 author is Jochen Wiedmann.
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.

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