/ 
ObjStore-1.21
River stage zero No dependents
/ ObjStore::Table2

NAME

ObjStore::Table2 - Simulated RDBMS Tables

SYNOPSIS

# posh 1.21 (Perl 5.00454 ObjectStore Release 5.0.1.0)
cd table-test ObjStore::Table2::Database

my $a = $db->array; for (1..10) { $a->_Push({row => $_}) }

$db->table->new_index('Field', 'row');
$db->table->build_indices;

DESCRIPTION

$at = TABLE ObjStore::Table2 {
 array[10] of ObjStore::HV {
   row => 1,
 },
 indices: ROW;
},

Unstructured perl databases are probably under-constrained for most applications. Tables standardize the interface for storing a bunch of records and their associated indices.

Raw Representation

$at = ObjStore::Table2 {
 _array => ObjStore::AV [
   ObjStore::HV {
     row => 1,
   },
   ObjStore::HV {
     row => 2,
   },
   ObjStore::HV {
     row => 3,
   },
   ...
 ],
 _index_segments => 1,
 row => ObjStore::Table::Index::Field {
   _field => 'row',
   _name => 'row',
   _segment => 6,
   _table => ObjStore::Ref => ObjStore::Table2 ...
   ctime => 882030349,
   map => ObjStore::HV {
     1 => ObjStore::HV ...
     10 => ObjStore::HV ...
     2 => ObjStore::HV ...
     ...
   },
   row => ObjStore::HV ...
 },
},

API

  • $t->index($index_name)

    Returns the index named $index_name.

  • $t->fetch($index_name, $key)

    Returns the record resulting from looking up $key in the index named $index_name.

  • $t->index_segments($yes)

    Indices can be allocated in their own segments or in the same segment as the table array. The default is to use separate segments.

  • $t->new_index($type, @ARGS)

    Creates an index of type $type using @ARGS and adds it to the table.

  • $t->add_index($index)

    Adds the given index to the table.

  • $t->remove_index($index)

  • $t->build_indices

  • $t->rebuild_indices

  • $t->drop_indices

  • $t->repair_indices($rec, $array_index)

    Attempt to repair all indices after a change at $array_index. $rec is the record that was added or deleted at $array_index.

  • $t->map_indices($coderef)

    Invokes $coderef->($index) over each index.

Representation Independent API

A database can essentially be a table or tables can be stored within a database. The implementation is only slightly different in either case. To smooth things over, a few accessor methods are provided that always work consistently.

  • $t->table

    Returns the top-level hash.

  • $t->array

    Returns the row array.

ObjStore::Table::Index

Base class for indices.

  • $class->new($table, $name)

    Adds an index called $name to the given table.

  • $i->name

    Returns the name of the index.

  • $i->table

    Returns the table to which the index is attached.

  • $i->build

  • $i->is_built

  • $i->drop

    Frees the index but preserves enough information to rebuild it.

  • $i->rebuild

  • $i->set_index_segment($segment)

    Sets the segment where the index will be created. May only be called once. A different API will be available for multisegment indices.

ObjStore::Table::Index::Field

$table->new_index('Field', $name, $field)

A basic unique index over all records. $field is an access path into the records to be indexed. For example, if your records looks like this:

{ f1 => [1,2,3] }

The access path would be "f1->0" to index the zeroth element of the array at hash key f1.

ObjStore::Table::Index::GroupBy

$table->new_index('GroupBy', $name, $field);

Groups all records into arrays indexed by $field. $field is an access path into the records to be indexed.

MIGRATION

Both ObjStore::HV::Database and ObjStore::Table are bless-migratible to ObjStore::Table2.

The old ObjStore::Table stored all indices in a hash under the top-level. Table2 stores them directly in the top-level. This should make index lookups slightly more efficient.

BUGS

Usage is a bit more cumbersome than I would like. The interface will change slightly as perl supports more overload-type features.

TODO

  • Automatic index maintanance: the array will be overloaded such that adds/deletes optionally trigger index updates

  • More built-in index types

AUTHOR

Copyright (c) 1997 Joshua Nathaniel Pritikin. All rights reserved.

This package is free software; you can redistribute it and/or modify it under the same terms as perl itself. This software is provided "as is" without express or implied warranty.