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Author image H.Merijn Brand
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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");

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 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

DBD::File

This is the base class for DBD::CSV, and it is included in the DBI distribution. As DBD::CSV requires version 0.37 or newer for DBD::File it effectively requires DBI version 1.609 or newer.

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.

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. ExtUtils::MakeMaker.

Supported SQL Syntax

All SQL processing for DBD::CSV is done by the SQL::Statement module. Features include joins, aliases, built-in and user-defined functions, and more. See SQL::Statement::Sytax for a description of the SQL syntax supported in DBD::CSV.

Table names are case insensitive unless quoted.

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

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 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(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, 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 $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(3) for details on these methods. See SQL::Statement(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 $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

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
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 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

DBD-CSV specific database handle attributes

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.

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;
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 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 distinquish 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 most likely to be only 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.

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 and sanitzes 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 (.). 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. 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.

Example: Suggest you want to use /etc/passwd as a CSV file. :-) There simplest way is:

    use 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   => [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 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 "Creating and dropping tables" above.

KNOWN ISSUES

  • 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).

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

Add 'sane_colnames' attribute to allow weird characters in col_names. Translate all illegal characters to '_' like mdb_tools does.

 s{[-\x00-\x20'":;.,/\\]}{_}g for @$row;
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.

Encoding

Test how well UTF-8 is supported, if not (yet), enable UTF-8, and maybe even more.

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(3), Text::CSV_XS(3), SQL::Statement(3)

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>

The original author is Jochen Wiedmann. Previous maintainer was Jeff Zucker

COPYRIGHT AND LICENSE

Copyright (C) 2009 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.