phpman > perldoc > DBD::SQLite::VirtualTable::PerlData(3pm)

NAME
    DBD::SQLite::VirtualTable::PerlData -- virtual table hooked to Perl data

SYNOPSIS
    Within Perl :

      $dbh->sqlite_create_module(perl => "DBD::SQLite::VirtualTable::PerlData");

    Then, within SQL :

      CREATE VIRTUAL TABLE atbl USING perl(foo, bar, etc,
                                           arrayrefs="some::global::var::aref")

      CREATE VIRTUAL TABLE htbl USING perl(foo, bar, etc,
                                           hashrefs="some::global::var::href")

      CREATE VIRTUAL TABLE ctbl USING perl(single_col
                                           colref="some::global::var::ref")


      SELECT foo, bar FROM atbl WHERE ...;

DESCRIPTION
    A "PerlData" virtual table is a database view on some datastructure within a Perl program. The
    data can be read or modified both from SQL and from Perl. This is useful for simple
    import/export operations, for debugging purposes, for joining data from different sources, etc.

PARAMETERS
    Parameters for creating a "PerlData" virtual table are specified within the "CREATE VIRTUAL
    TABLE" statement, mixed with regular column declarations, but with an '=' sign.

    The only authorized (and mandatory) parameter is the one that specifies the Perl datastructure
    to which the virtual table is bound. It must be given as the fully qualified name of a global
    variable; the parameter can be one of three different kinds :

    "arrayrefs"
        arrayref that contains an arrayref for each row. Each such row will have a size equivalent
        to the number of columns declared for the virtual table.

    "hashrefs"
        arrayref that contains a hashref for each row. Keys in each hashref should correspond to the
        columns declared for the virtual table.

    "colref"
        arrayref that contains a single scalar for each row; obviously, this is a single-column
        virtual table.

USAGE
  Common part of all examples : declaring the module
    In all examples below, the common part is that the Perl program should connect to the database
    and then declare the "PerlData" virtual table module, like this

      # connect to the database
      my $dbh = DBI->connect("dbi:SQLite:dbname=$dbfile", '', '',
                              {RaiseError => 1, AutoCommit => 1});
                              # or any other options suitable to your needs

      # register the module
      $dbh->sqlite_create_module(perl => "DBD::SQLite::VirtualTable::PerlData");

    Then create a global arrayref variable, using "our" instead of "my", so that the variable is
    stored in the symbol table of the enclosing module.

      package Foo::Bar; # could as well be just "main"
      our $rows = [ ... ];

    Finally, create the virtual table and bind it to the global variable (here we assume that @$rows
    contains arrayrefs) :

      $dbh->do('CREATE VIRTUAL TABLE temp.vtab'
              .'  USING perl(col1 INT, col2 TEXT, etc,
                             arrayrefs="Foo::Bar::rows');

    In most cases, the virtual table will be for temporary use, which is the reason why this example
    prepends "temp." in front of the table name : this tells SQLite to cleanup that table when the
    database handle will be disconnected, without the need to emit an explicit DROP statement.

    Column names (and optionally their types) are specified in the virtual table declaration, just
    like for any regular table.

  Arrayref example : statistics from files
    Let's suppose we want to perform some searches over a collection of files, where search
    constraints may be based on some of the fields returned by stat, such as the size of the file or
    its last modify time. Here is a way to do it with a virtual table :

      my @files = ... ; # list of files to inspect

      # apply the L<stat> function to each file
      our $file_stats = [ map { [ $_, stat $_ ] } @files];

      # create a temporary virtual table
      $dbh->do(<<"");
         CREATE VIRTUAL TABLE temp.file_stats'
            USING perl(path, dev, ino, mode, nlink, uid, gid, rdev, size,
                             atime, mtime, ctime, blksize, blocks,
                       arrayrefs="main::file_stats");

      # search files
      my $sth = $dbh->prepare(<<"");
        SELECT * FROM file_stats
          WHERE mtime BETWEEN ? AND ?
            AND uid IN (...)

  Hashref example : unicode characters
    Given any unicode character, the "charinfo" in Unicode::UCD function returns a hashref with
    various bits of information about that character. So this can be exploited in a virtual table :

      use Unicode::UCD 'charinfo';
      our $chars = [map {charinfo($_)} 0x300..0x400]; # arbitrary subrange

      # create a temporary virtual table
      $dbh->do(<<"");
        CREATE VIRTUAL TABLE charinfo USING perl(
          code, name, block, script, category,
          hashrefs="main::chars"
         )

      # search characters
      my $sth = $dbh->prepare(<<"");
        SELECT * FROM charinfo
         WHERE script='Greek'
           AND name LIKE '%SIGMA%'

  Colref example: SELECT WHERE ... IN ...
    *Note: The idea for the following example is borrowed from the "test_intarray.h" file in
    SQLite's source (<http://www.sqlite.org/src>).*

    A "colref" virtual table is designed to facilitate using an array of values as the right-hand
    side of an IN operator. The usual syntax for IN is to prepare a statement like this:

        SELECT * FROM table WHERE x IN (?,?,?,...,?);

    and then bind individual values to each of the ? slots; but this has the disadvantage that the
    number of values must be known in advance. Instead, we can store values in a Perl array, bind
    that array to a virtual table, and then write a statement like this

        SELECT * FROM table WHERE x IN perl_array;

    Here is how such a program would look like :

      # connect to the database
      my $dbh = DBI->connect("dbi:SQLite:dbname=$dbfile", '', '',
                              {RaiseError => 1, AutoCommit => 1});

      # Declare a global arrayref containing the values. Here we assume
      # they are taken from @ARGV, but any other datasource would do.
      # Note the use of "our" instead of "my".
      our $values = \@ARGV;

      # register the module and declare the virtual table
      $dbh->sqlite_create_module(perl => "DBD::SQLite::VirtualTable::PerlData");
      $dbh->do('CREATE VIRTUAL TABLE temp.intarray'
              .'  USING perl(i INT, colref="main::values');

      # now we can SELECT from another table, using the intarray as a constraint
      my $sql    = "SELECT * FROM some_table WHERE some_col IN intarray";
      my $result = $dbh->selectall_arrayref($sql);

    Beware that the virtual table is read-write, so the statement below would push 99 into @ARGV !

      INSERT INTO intarray VALUES (99);

AUTHOR
    Laurent Dami <dami AT cpan.org>

COPYRIGHT AND LICENSE
    Copyright Laurent Dami, 2014.

    This library is free software; you can redistribute it and/or modify it under the same terms as
    Perl itself.