| DBD::CSV(3pm) | User Contributed Perl Documentation | DBD::CSV(3pm) |
DBD::CSV - DBI driver for CSV files
use DBI;
# See "Creating database handle" below
$dbh = DBI->connect ("dbi:CSV:", undef, undef, {
f_ext => ".csv/r",
RaiseError => 1,
}) or die "Cannot connect: $DBI::errstr";
# Simple statements
$dbh->do ("CREATE TABLE foo (id INTEGER, name CHAR (10))");
# Selecting
my $sth = $dbh->prepare ("select * from foo");
$sth->execute;
$sth->bind_columns (\my ($id, $name));
while ($sth->fetch) {
print "id: $id, name: $name\n";
}
# Updates
my $sth = $dbh->prepare ("UPDATE foo SET name = ? WHERE id = ?");
$sth->execute ("DBI rocks!", 1);
$sth->finish;
$dbh->disconnect;
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 often used for exporting MS Access and MS Excel data.
See DBI for details on DBI, SQL::Statement for details on SQL::Statement and DBD::File for details on the base class DBD::File.
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
http://search.cpan.org/
It is possible to run "DBD::CSV" without this module if you define the environment variable $DBI_SQL_NANO to 1. This will reduce the SQL support a lot though. See DBI::SQL::Nano for more details. Note that the test suite does only test in this mode in the development environment.
Installing this module (and the prerequisites from above) is quite simple. The simplest way is to install the bundle:
$ cpan Bundle::DBD::CSV
Alternatively, you can name them all
$ cpan Text::CSV_XS DBI DBD::CSV
or even trust "cpan" to resolve all dependencies for you:
$ cpan DBD::CSV
If you cannot, for whatever reason, use cpan, fetch all modules from CPAN, and build with a sequence like:
gzip -d < DBD-CSV-0.40.tgz | tar xf -
(this is for Unix users, Windows users would prefer WinZip or something similar) and then enter the following:
cd DBD-CSV-0.40
perl Makefile.PL
make test
If any tests fail, let us know. Otherwise go on with
make install UNINST=1
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. ExtUtils::MakeMaker.
All SQL processing for DBD::CSV is done by SQL::Statement. See SQL::Statement for more specific information about its feature set. Features include joins, aliases, built-in and user-defined functions, and more. See SQL::Statement::Syntax for a description of the SQL syntax supported in DBD::CSV.
Table- and column-names are case insensitive unless quoted. Column names will be sanitized unless "raw_header" is true.
For most things, DBD-CSV operates the same as any DBI driver. See DBI for detailed usage.
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 => "/home/user/folder",
});
The directory tells the driver where it should create or open tables (a.k.a. files). It defaults to the current directory, so the following are equivalent:
$dbh = DBI->connect ("dbi:CSV:");
$dbh = DBI->connect ("dbi:CSV:", undef, undef, { f_dir => "." });
$dbh = DBI->connect ("dbi:CSV:f_dir=.");
We were told, that VMS might - for whatever reason - require:
$dbh = DBI->connect ("dbi:CSV:f_dir=");
The preferred way of passing the arguments is by driver attributes:
# specify most possible flags via driver flags
$dbh = DBI->connect ("dbi:CSV:", undef, undef, {
f_schema => undef,
f_dir => "data",
f_dir_search => [],
f_ext => ".csv/r",
f_lock => 2,
f_encoding => "utf8",
csv_eol => "\r\n",
csv_sep_char => ",",
csv_quote_char => '"',
csv_escape_char => '"',
csv_class => "Text::CSV_XS",
csv_null => 1,
csv_bom => 0,
csv_tables => {
syspwd => {
sep_char => ":",
quote_char => undef,
escape_char => undef,
file => "/etc/passwd",
col_names => [qw( login password
uid gid realname
directory shell )],
},
},
RaiseError => 1,
PrintError => 1,
FetchHashKeyName => "NAME_lc",
}) or die $DBI::errstr;
but you may set these attributes in the DSN as well, separated by semicolons. Pay attention to the semi-colon for "csv_sep_char" (as seen in many CSV exports from MS Excel) is being escaped in below example, as is would otherwise be seen as attribute separator:
$dbh = DBI->connect (
"dbi:CSV:f_dir=$ENV{HOME}/csvdb;f_ext=.csv;f_lock=2;" .
"f_encoding=utf8;csv_eol=\n;csv_sep_char=\\;;" .
"csv_quote_char=\";csv_escape_char=\\;csv_class=Text::CSV_XS;" .
"csv_null=1") or die $DBI::errstr;
Using attributes in the DSN is easier to use when the DSN is derived from an outside source (environment variable, database entry, or configure file), whereas specifying entries in the attribute hash is easier to read and to maintain.
The default value for "csv_binary" is 1 (True).
The default value for "csv_auto_diag" is <1>. Note that this might cause trouble on perl versions older than 5.8.9, so up to and including perl version 5.8.8 it might be required to use ";csv_auto_diag=0" inside the "DSN" or "csv_auto_diag =" 0> inside the attributes.
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 DBI 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.
The following examples insert some data in a table and fetch it back: First, an example where the column data is concatenated in the SQL 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 does not 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 quote column data passed as parameters. 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 used and will be passed to the prepare method as the 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 $sth = $dbh->prepare (qq;
SELECT * FROM $table WHERE id > 1 ORDER BY id;
;);
$sth->execute;
my ($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 $sth = $dbh->prepare ("SELECT * FROM $table WHERE id = ?");
$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 DBI for details on these methods. See SQL::Statement 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");
In the above examples we have never cared about return codes. Of course, this is not recommended. Instead we should have written (for example):
my $sth = $dbh->prepare ("SELECT * FROM $table WHERE id = ?") 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 ();
$sth->fetch and
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 $sth = $dbh->prepare ("SELECT * FROM $table WHERE id = ?");
$sth->bind_columns (undef, \$id, \$name);
for (my $i = 1; $i <= 2; $i++) {
$sth->execute ($id);
$sth->fetch and
print "Found result row: id = $id, name = $name\n";
}
$sth->finish ($id);
};
$@ and die "SQL database error: $@";
This is not only shorter, it even works when using DBI methods within subroutines.
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:
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:
my $dbh = DBI->connect ("dbi:CSV:", "", "", {
f_dir => "data",
f_dir_search => [ "ref/data", "ref/old" ],
f_ext => ".csv/r",
}) or die $DBI::errstr;
my $dbh = DBI->connect ("dbi:CSV:", "", "", {
f_schema => undef,
f_dir => "data",
f_ext => ".csv/r",
}) or die $DBI::errstr;
But see "KNOWN BUGS" in DBD::File.
In order to use the specified class other than "Text::CSV_XS", it needs to be loaded before use. "DBD::CSV" does not "require"/"use" the specified class itself.
The csv_eol attribute defines the end-of-line pattern, which is better known as a record separator pattern since it separates records. The default is windows-style end-of-lines "\015\012" for output (writing) and unset for input (reading), so if on unix you may want to set this to newline ("\n") like this:
$dbh->{csv_eol} = "\n";
It is also possible to use multi-character patterns as record separators. For example this file uses newlines as field separators (sep_char) and the pattern "\n__ENDREC__\n" as the record separators (eol):
name
city
__ENDREC__
joe
seattle
__ENDREC__
sue
portland
__ENDREC__
To handle this file, you'd do this:
$dbh->{eol} = "\n__ENDREC__\n" ,
$dbh->{sep_char} = "\n"
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.
$dbh = DBI->connect ("dbi:CSV:", "", "", { csv_null => 1 });
$dbh->{csv_null} = 1;
$dbh = DBI->connect ("dbi:CSV:", "", "", { csv_bom => 1 });
$dbh->{csv_bom} = 1;
If you pass it "f_file" or its alias "file", "f_ext" has no effect, but "f_dir" and "f_encoding" still have.
csv_tables => {
syspwd => { # Table name
csv_sep_char => ":", # Text::CSV_XS
quote_char => undef, # Text::CSV_XS
escape_char => undef, # Text::CSV_XS
f_dir => "/etc", # DBD::File
f_file => "passwd", # DBD::File
col_names => # DBD::File
[qw( login password uid gid realname directory shell )],
},
},
$dbh->{csv_allow_whitespace} = 1;
$dbh->{csv_allow_loose_quotes} = 1;
$dbh->{csv_allow_loose_escapes} = 1;
See the "Text::CSV_XS" documentation for the full list and the documentation.
"$dbh->{f_dir}/$table"
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", ...
Note that column names that match reserved SQL words will cause unwanted and sometimes confusing errors. If your CSV has headers that match reserved words, you will require these two attributes.
If "test.csv" looks like
select,from
1,2
the select query would result in "select select, from from test;", which obviously is illegal SQL.
Currently, the sanitizing of headers is as simple as
s/\W/_/g;
Note that headers (column names) might be folded in other parts of the code stack, specifically SQL::Statement, whose docs mention:
Wildcards are expanded to lower cased identifiers. This might
confuse some people, but it was easier to implement.
That means that in
my $sth = $dbh->prepare ("select * from foo");
$sth->execute;
while (my $row = $sth->fetchrow_hashref) {
say for keys %$row;
}
all keys will show as all lower case, regardless of the original header.
It's strongly recommended to check the attributes supported by "Metadata" in DBD::File.
Example: Suppose you want to use /etc/passwd as a CSV file. :-) There simplest way is:
use DBI;
my $dbh = DBI->connect ("dbi:CSV:", undef, undef, {
f_dir => "/etc",
csv_sep_char => ":",
csv_quote_char => undef,
csv_escape_char => undef,
});
$dbh->{csv_tables}{passwd} = {
col_names => [qw( 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 override them on a per table basis:
require DBI;
my $dbh = DBI->connect ("dbi:CSV:");
$dbh->{csv_tables}{passwd} = {
eol => "\n",
sep_char => ":",
quote_char => undef,
escape_char => undef,
f_file => "/etc/passwd",
col_names => [qw( login password uid gid
realname directory shell )],
};
$sth = $dbh->prepare ("SELECT * FROM passwd");
These methods are inherited from DBD::File:
If you want to read the sub-directories of another directory, use
my $drh = DBI->install_driver ("CSV");
my @list = $drh->data_sources (f_dir => "/usr/local/csv_data");
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 "Creating and dropping tables" above.
- eol Make tests for different record separators.
- csv_xs Test with a variety of combinations for
sep_char, quote_char, and escape_char testing
- quoting $dbh->do ("drop table $_") for DBI-tables ();
- errors Make sure that all documented exceptions are tested.
. write to write-protected file
. read from badly formatted csv
. pass bad arguments to csv parser while fetching
Add tests that specifically test DBD::File functionality where that is useful.
DBI, Text::CSV_XS, SQL::Statement, DBI::SQL::Nano
For help on the use of DBD::CSV, see the DBI users mailing list:
http://lists.cpan.org/showlist.cgi?name=dbi-users
For general information on DBI see
http://dbi.perl.org/ and http://faq.dbi-support.com/
This module is currently maintained by
H.Merijn Brand <h.m.brand@xs4all.nl>
in close cooperation with and help from
Jens Rehsack <sno@NetBSD.org>
The original author is Jochen Wiedmann. Previous maintainer was Jeff Zucker
Copyright (C) 2009-2023 by H.Merijn Brand Copyright (C) 2004-2009 by Jeff Zucker Copyright (C) 1998-2004 by 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.
| 2023-01-15 | perl v5.36.0 |