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();

WARNING
    THIS IS ALPHA SOFTWARE. It is *only* 'Alpha' because the interface (API)
    is not finalised. 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 Acess 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, on Windows 95 and
    NT.

    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 0.93 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.

  Creating a database handle

    Creating a database handle usually implies connecting to a database
    server. Thus this command reads

        use DBI;
        my $dbh = DBI->connect("DBI:File:f_dir=$dir");

    The directory tells the driver where it should create or open tables
    (aka files). It defaults to the current directory, thus the following
    are equivalent:

        $dbh = DBI->connect("DBI:File:");
        $dbh = DBI->connect("DBI:File: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 table names to be 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 (?, ?)",
                 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.

    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 for 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 like 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

    Additional 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_class
    csv_csv Used as a default for the respective attributes of *csv_tables*, see
            below.

    csv_tables
            This hash ref is used for storing table dependent meta data. 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

    csv_class           The class to use for accessing the file, by default
                        "Text::CSV_XS". This attribute (like any other
                        attribute of prefix *csv_*, see *csv_csv* below) is
                        inherited from the dbh, if not explicitly specified.

    csv_csv             The csv object, an instance of *csv_class*. You need to
                        supply such an object for overwriting attributes
                        like `$csv-'{eol}>, `$csv-'{quote_char}> and the
                        like. See the Text::CSV_XS(3) manpage for details.
                        Note that by default binary mode is used for
                        creating the csv object. You must not change this!

    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. :-
            ) You can read it like this:

                require DBI;
                my $dbh = DBI->connect("DBI:CSV:f_dir=/etc");
                my $dbh->{csv_tables}->{passwd} = {
                    csv_csv => Text::CSV_XS->new({ binary => 1,
                                                   eol => "\012",
                                                   quote_char => undef,
                                                   escape_char => undef,
                                                   sep_char => ':'}),
                    file => '/etc/passwd',
                    col_names => ["login", "password", "uid", "gid", "realname",
                                  "directory", "shell"]
                };
                $dbh->do("UPDATE passwd SET login = 'joe' WHERE login = 'wiedmann'");

  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". Unfortunately the current
                version of DBI doesn't accept attributes of the data_sources
                method. Thus the method reads a global variable

                    $DBD::CSV::dr::data_sources_attr

                if you want to read the subdirectories of another directory.
                Example:

                    my($drh) = DBI->install_driver("CSV");
                    $DBD::CSV::dr::data_sources_attr = "/usr/local/csv_data";
                    my(@list) = $drh->data_sources();

    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 NULL's. 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
            These are merely restrictions of the DBD::File or SQL::Statement
            modules:

    Joins       The current version of the module works with single table
                SELECT's only, although the basic design of the
                SQL::Statement module allows joins and the likes.

    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.

AUTHOR AND COPYRIGHT
            This module is Copyright (C) 1998 by

                Jochen Wiedmann
                Am Eisteich 9
                72555 Metzingen
                Germany

                Email: joe@ispsoft.de
                Phone: +49 7123 14887

            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

