NAME¶
DBD::CSV - DBI driver for CSV files
SYNOPSIS¶
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;
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 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.
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
http://search.cpan.org/
- DBI
- A recent version of the DBI (Database independent interface for Perl). See
below why.
- DBD::File
- This is the base class for DBD::CSV, and it is part of the DBI
distribution. As DBD::CSV requires a matching version of DBD::File which
is (partly) developed by the same team that maintains DBD::CSV. See
META.json or Makefile.PL for the minimum versions.
- SQL::Statement
- A simple SQL engine. This module defines all of the SQL syntax for
DBD::CSV, new SQL support is added with each release so you should look
for updates to SQL::Statement regularly.
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.
- Text::CSV_XS
- This module is used to read and write rows in a CSV file.
Installation¶
Installing this module (and the prerequisites from above) is quite simple. The
simplest way is to install the bundle:
$ cpan Bundle::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.
Supported SQL Syntax¶
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;
Using DBD::CSV with DBI¶
For most things, DBD-CSV operates the same as any DBI driver. See DBI for
detailed usage.
Creating a database handle (connect)¶
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_tables => {
info => { f_file => "info.csv" }
},
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.
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 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.
Inserting, fetching and modifying data¶
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");
Error handling¶
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: $@";
This is not only shorter, it even works when using DBI methods within
subroutines.
DBI database handle attributes¶
The following attributes are handled by DBI itself and not by DBD::File, thus
they all work as expected:
Active
ActiveKids
CachedKids
CompatMode (Not used)
InactiveDestroy
Kids
PrintError
RaiseError
Warn (Not used)
The following DBI attributes are handled by DBD::File:
- AutoCommit
- Always on
- ChopBlanks
- Works
- NUM_OF_FIELDS
- Valid after "$sth->execute"
- NUM_OF_PARAMS
- Valid after "$sth->prepare"
- NAME
- NAME_lc
- NAME_uc
- Valid after "$sth->execute"; undef for Non-Select
statements.
- NULLABLE
- Not really working. Always returns an array ref of one's, as DBD::CSV does
not 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
DBD-CSV specific database handle attributes¶
In addition to the DBI attributes, you can use the following dbh attributes:
DBD::File attributes¶
- f_dir
- This attribute is used for setting the directory where CSV files are
opened. Usually you set it in the dbh and it defaults to the current
directory ("."). However, it may be overridden in statement
handles.
- f_dir_search
- This attribute optionally defines a list of extra directories to search
when opening existing tables. It should be an anonymous list or an array
reference listing all folders where tables could be found.
my $dbh = DBI->connect ("dbi:CSV:", "", "", {
f_dir => "data",
f_dir_search => [ "ref/data", "ref/old" ],
f_ext => ".csv/r",
}) or die $DBI::errstr;
- f_ext
- This attribute is used for setting the file extension.
- f_schema
- This attribute allows you to set the database schema name. The default is
to use the owner of "f_dir". "undef" is allowed, but
not in the DSN part.
my $dbh = DBI->connect ("dbi:CSV:", "", "", {
f_schema => undef,
f_dir => "data",
f_ext => ".csv/r",
}) or die $DBI::errstr;
- f_encoding
- This attribute allows you to set the encoding of the data. With CSV, it is
not possible to set (and remember) the encoding on a column basis, but
DBD::File now allows the encoding to be set on the underlying file. If
this attribute is not set, or undef is passed, the file will be seen as
binary.
- f_lock
- With this attribute you can specify a locking mode to be used (if locking
is supported at all) for opening tables. By default, tables are opened
with a shared lock for reading, and with an exclusive lock for writing.
The supported modes are:
- 0
- Force no locking at all.
- 1
- Only shared locks will be used.
- 2
- Only exclusive locks will be used.
But see "KNOWN BUGS" in DBD::File.
DBD::CSV specific attributes¶
- csv_class
- The attribute csv_class controls the CSV parsing engine. This
defaults to "Text::CSV_XS", but "Text::CSV" can be
used in some cases, too. Please be aware that "Text::CSV" does
not care about any edge case as "Text::CSV_XS" does and that
"Text::CSV" is probably about 100 times slower than
"Text::CSV_XS".
Text::CSV_XS specific attributes¶
- csv_eol
- csv_sep_char
- csv_quote_char
- csv_escape_char
- csv_csv
- The attributes csv_eol, csv_sep_char, csv_quote_char
and csv_escape_char are corresponding to the respective attributes
of the csv_class (usually Text::CSV_CS) object. You may 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 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.
- csv_null
- With this option set, all new statement handles will set
"always_quote" and "blank_is_undef" in the CSV parser
and writer, so it knows how to distinguish between the empty string and
"undef" or "NULL". You cannot reset it with a false
value. You can pass it to connect, or set it later:
$dbh = DBI->connect ("dbi:CSV:", "", "", { csv_null => 1 });
$dbh->{csv_null} = 1;
- 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:
- csv_*
- All other attributes that start with "csv_" and are not
described above will be passed to "Text::CSV_XS" (without the
"csv_" prefix). These extra options are only likely to be useful
for reading (select) handles. Examples:
$dbh->{csv_allow_whitespace} = 1;
$dbh->{csv_allow_loose_quotes} = 1;
$dbh->{csv_allow_loose_escapes} = 1;
See the "Text::CSV_XS" documentation for the full list and the
documentation.
Driver specific attributes¶
- f_file
- The name of the file used for the table; defaults to
"$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
basis.
- col_names
- skip_first_row
- By default DBD::CSV assumes that column names are stored in the first row
of the CSV file and sanitizes them (see "raw_header" below). 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", ...
- raw_header
- Due to the SQL standard, field names cannot contain special characters
like a dot (".") or a space (" ") unless the column
names are quoted. Following the approach of mdb_tools, all these tokens
are translated to an underscore ("_") when reading the first
line of the CSV file, so all field names are 'sanitized'. If you do not
want this to happen, set "raw_header" to a true value and the
entries in the first line of the CSV data will be used verbatim for column
headers and field names. DBD::CSV cannot guarantee that any part in the
toolchain will work if field names have those characters, and the chances
are high that the SQL statements will fail.
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 = $dbh->prepare ("SELECT * FROM passwd");
Driver private methods¶
These methods are inherited from DBD::File:
- data_sources
- The "data_sources" method returns a list of sub-directories of
the current directory in the form "dbi:CSV:directory=$dirname".
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");
- 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 "Creating
and dropping tables" above.
KNOWN ISSUES¶
- •
- The module is using flock () internally. However, this function is not
available on some platforms. Use of 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).
TODO¶
- Tests
- Aim for a full 100% code coverage
- 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 $_") for DBI-tables ();
- errors Make sure that all documented exceptions are tested.
. write to write-protected file
. read from badly formatted csv
. pass bad arguments to csv parser while fetching
Add tests that specifically test DBD::File functionality where that is
useful.
- RT
- Attack all open DBD::CSV bugs in RT
- CPAN::Forum
- Attack all items in http://www.cpanforum.com/dist/DBD-CSV
- Documentation
- Expand on error-handling, and document all possible errors. Use
Text::CSV_XS::error_diag () wherever possible.
- Debugging
- Implement and document dbd_verbose.
- Data dictionary
- Investigate the possibility to store the data dictionary in a file like
.sys$columns that can store the field attributes (type, key,
nullable).
- Examples
- Make more real-life examples from the docs in examples/
SEE ALSO¶
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/
AUTHORS and MAINTAINERS¶
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 AND LICENSE¶
Copyright (C) 2009-2014 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.