NAME

DBIx::Tree - Perl module for generating a tree from a self-referential table

SYNOPSIS

use DBIx::Tree;
# have DBIx::Tree build the necessary SQL from table & column names:
my $tree = new DBIx::Tree(connection => $dbh,
                          table      => $table,
                          method     => sub { disp_tree(@_) },
                          columns    => [$id_col, $label_col, $parent_col],
                          start_id   => $start_id);
$tree->traverse;

# alternatively, use your own custom SQL statement

my $sql = <<EOSQL;
SELECT nodes.id, labels.label, nodes.parent_id
FROM nodes
INNER JOIN labels
ON nodes.id = labels.node_id
WHERE labels.type = 'preferred label'
ORDER BY label ASC

EOSQL

my $tree = new DBIx::Tree(connection => $dbh,
                          sql        => $sql,
                          method     => sub { disp_tree(@_) },
                          columns    => ['id', 'label', 'parent_id'],
                          start_id   => $start_id);

$tree->traverse;

# or use an already prepared DBI statement handle:

my $sth = $dbh->prepare($sql);
my $tree = new DBIx::Tree(connection => $dbh,
                          sth        => $sth,
                          method     => sub { disp_tree(@_) },
                          columns    => ['id', 'label', 'parent_id'],
                          start_id   => $start_id);

$tree->traverse;

DESCRIPTION

When you've got one of those nasty self-referential tables that you want to bust out into a tree, this is the module to check out. Assuming there are no horribly broken nodes in your tree and (heaven forbid) any circular references, this module will turn something like:

food                food_id   parent_id
==================  =======   =========
Food                001       NULL
Beans and Nuts      002       001
Beans               003       002
Nuts                004       002
Black Beans         005       003
Pecans              006       004
Kidney Beans        007       003
Red Kidney Beans    008       007
Black Kidney Beans  009       007
Dairy               010       001
Beverages           011       010
Whole Milk          012       011
Skim Milk           013       011
Cheeses             014       010
Cheddar             015       014
Stilton             016       014
Swiss               017       014
Gouda               018       014
Muenster            019       014
Coffee Milk         020       011

into:

Food (001)
  Dairy (010)
    Beverages (011)
      Coffee Milk (020)
      Whole Milk (012)
      Skim Milk (013)
    Cheeses (014)
      Cheddar (015)
      Stilton (016)
      Swiss (017)
      Gouda (018)
      Muenster (019)
  Beans and Nuts (002)
    Beans (003)
      Black Beans (005)
      Kidney Beans (007)
        Red Kidney Beans (008)
        Black Kidney Beans (009)
    Nuts (004)
      Pecans (006)

There are examples in the examples directory - one plain text example, and two Tk examples.

Constructor arguments

my $tree = new DBIx::Tree(connection => $dbh,
                          table      => $table,
                          sql        => $sql,
                          sth        => $sth,
                          method     => sub { disp_tree(@_) },
                          columns    => [$id_col, $label_col, $parent_col],
                          start_id   => $start_id,
                          threshold  => $threshold,
                          match_data => $match_data,
                          limit      => $limit
                          recursive  => 1 || 0);

connection

A DBI connection handle. Unnecessary if you plan to provide a prepared DBI statement handle via the 'sth' parameter.

table

The database table containing the hierarchical data. Unnecessary if you plan to provide either a custom SQL statement via the 'sql' parameter or a prepared DBI statement handle via the 'sth' parameter.

sql

A string containing a custom "SELECT" SQL query statement that returns the hierarchical data. Unnecessary if all of the id/label/parent columns come from the same table specified by the 'table' parameter. Use only when you need to bring in supplementary information from other tables via custom "joins". Note that providing an 'sql' argument will override any other 'table' specification.

sth

A prepared (but not yet executed!) DBI statement handle. Unnecessary if you plan to provide either a basic table name via 'table' or a custom SQL statement via 'sql'. Note that providing an 'sth' argument will override any other 'sql' or 'table' specification.

method

A callback method to be invoked each time a tree item is encountered. This method will be given a hashtable as a parameter, containing the following elements:

item:        the name of the item
level (0-n): the nesting level of the item.
id:          the unique id of the item.
parent_id:   an array ref containing the geneology of parent id's
             for the current item
parent_name: an array ref containing the geneology of parent name's
             for the current item

If the 'threshold' parameter has been set (either via the new() constructor or in the call to traverse()), the callback will only occur if the tree item is 'threshold' or more levels deep in the hierarchy.

post_method

A callback method to be invoked after all the children of a tree item have been encountered. This method will be given a hashtable as a parameter, containing the following elements:

item:        the name of the item
level (0-n): the nesting level of the item.
id:          the unique id of the item.
parent_id:   an array ref containing the geneology of parent id's
             for the current item
parent_name: an array ref containing the geneology of parent name's
             for the current item

If the 'threshold' parameter has been set (either via the new() constructor or in the call to traverse()), the callback will only occur if the tree item is 'threshold' or more levels deep in the hierarchy.

columns:

A reference to a list of three column names that can be found in the table/result set:

id_col:     The name of the column containing the unique id.
label_col:  The name of the column containing the textual data
            of the row, like a name.
parent_col: The name of the column containing the id of the
            row's parent.

Optional additional columns; note that these will only be used in queries built by DBIx::Tree from 'table' specifications - i.e. they will not be used with 'sth'- or 'sql'-type query parameters (presumably you can provide this functionality yourself when using one of those query types).

order_col:  The name of a column to use for ordering the results;
            defaults to the column name specified by label_col.
            This column name does not need to exist in the result
            set, but should exist in the table being queried.

order_dir:  An SQL directive specifying the directionality of the
            ordering; for most databases this is either 'ASC' or
            'DESC'.  The default is an empty string, which leaves
            the decision to the database (in most cases, this will
            be ascending)

start_id

The unique id of the root item. Defaults to 1. May be overriden by the 'start_id' argument to traverse().

threshold

The level in the hierarchical tree at which to begin processing items. The root of the tree is considered to be at level 1. May be overriden by the 'threshold' argument to traverse().

match_data

The value of a partial match to look for - if this is supplied, only rows whose label_col matches (match_data + '%') this will be selected. This feature was supplied by Ilia Lobsanov <ilia@lobsanov.com>

limit

Limit the number of rows using an SQL LIMIT clause - not all SQL servers support this. This feature was supplied by Ilia Lobsanov <ilia@lobsanov.com>

recursive

Specifies which of two methods DBIx::Tree will use to traverse the tree. The default is non-recursively, which is efficient in that it requires only a single database query, but it also loads the entire tree into memory at once. The recursive method queries the database repetitively, but has smaller memory requirements. The recursive method will also be more efficient when an alternative start_id is specified. Note that if you supply both a limit argument and a threshold argument (implying that you want to see at most N records at or below the given threshold), the recursive method will be used automatically for efficiency.

DBIx::Tree Methods

traverse(%args)

Begins a depth-first traversal of the hierarchical tree. The optional %args hash provides locally overriding values for the identical parameters set in the new() constructor.

TODO

Graceful handling of circular references. Better docs. Rewrite the algorithm. Separate data acquisition from data formatting.

AUTHOR

Brian Jepson, bjepson@ids.net

This module was inspired by the Expanding Hierarchies example that I stumbled across in the Microsoft SQL Server Database Developer's Companion section of the Microsoft SQL Server Programmer's Toolkit.

Jan Mach <machj@ders.cz> contributed substantial performance improvements, ordering handling for tree output, and other bug fixes.

Aaron Mackey <amackey@virginia.edu> has continued active development on the module based on Brian Jepson's version 0.91 release.

SEE ALSO

perl(1). DBI(3). Tk(3).