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Persistence::Database::SQL
Object Persistence in SQL Databases.

Persistence::Database::SQL - Object Persistence in SQL Databases.


NAME

Persistence::Database::SQL - Object Persistence in SQL Databases.


SYNOPSIS


  use Persistence::Database::SQL;

  my $db = new Persistence::Database::SQL

    ( Engine => 'Postgres',

      Database => $database_name, 

      Table => $table_name,

      Template => $template_hashref );

  my (@objects) = $db->search

    ( Key => $key,

      Regex => $regex );

  for $obj (@objects) {

    $db->table('expired'); 

    $obj->commit();

    $db->table($table_name); 

    $obj->expire();

  }

  my $dbhandle = $db->dbhandle();

  my $query = "SELECT oid,* FROM $table_name WHERE $field=$value";

  my $sth = $dbhandle->prepare($query); $sth->execute();

  while (@row = $sth->fetchrow()) {

    my $obj = new Persistence::Object::Postgres

      ( __Dope => $db,

        __Oid => $row[0] );

    $obj->expire();

  }


DESCRIPTION

This module provides a store of persistent objects using various DBMS engines. It works in association with a lower level persistent object implementation, such as Persistence::Object::Postgres.

Using a template mapping object properties to PostgreSQL class fields, it is possible to automatically generate DBMS fields out of the object data, which allows you to use SQL indexing and querying facilities on your database of persistent objects.


CONSTRUCTOR

new()
Creates a new Database Object.

  my $database = new Persistence::Database::SQL

    ( 

      Engine => 'Postgres',           # Required

      Database => $database_name, 

      Table => $table_name,

      Template => $template_hashref,

      Host => $db_host,               # Optional

      Port => $db_port,

      Username => $db_username,

      Password => $db_password

      Createfields => $boolean,

      Createtables => $boolean

    );

Takes a hash argument with following possible keys:

Engine

The name of the underlying DBMS engine, for which there must be a Persistence::Object::Engine class available. Currently, the only available engine is 'Postgres'. This attribute is required.

Database

The name of the database. A database by this name must exist previously within the DBMS system in use with sufficient priveleges for the user. This attribute is required.

Table

The table within the database to use for object storage. A table by this name must exist previously within the DBMS system in use with sufficient priveleges for the user. This attribute is required, and can be later changed with the table() method.

Template

A reference to a hash that maps persistent object key names to database field names. Key names that are mapped in the template will be extracted and stored in separate database fields. In the degenerate case where you provide an empty hash for the mapping template, only the complete object dump is stored.

The complete object dump will always be stored, in a database field called __dump, which will be created if it doesn't exist. If the database user doesn't have sufficient priveleges to alter tables, and the __dump field doesn't exist in the database, commit() will fail.

This attribute is required, and can be later changed with the template() method.

Host

The name or IP address of the database server. A default value is provided by the DBMS-specific object class if this attribute is omitted.

Port

The port on which the database server can be accessed. A default value is provided by the DBMS-specific object class if this attribute is omitted.

Username

The username to use to acccess the database server. A default value, usually the username of the user running the program, is provided by the DBMS-specific object class if this attribute is omitted.

Password

The password for the user. A default value may be provided by the DBMS-specific object class if this attribute is omitted, though it would probably be an empty string.

Createfields

Whether or not new fields should be created in the database to meet the needs of complying with the mapping template. If true, fields will silently be created in the database. For this to work, the database user must have sufficient priveleges within the database system.

If false, data will not be stored in a separate database field even if a mapping for it exists in the template, unless the field in question already exists in the database.

The default is true. This attribute can be queried and changed on the fly with the createfields() method.

Createtables

Whether or not new tables should be created in the database if they are referenced but don't already exist. If true, tables will automatically be created as needed. For this to work, the database user must have sufficient priveleges within the database system.

If false, tables will not be automatically created, which will cause commit() and load() to fail if asked to operate on a nonexistent table.

The default is true. This attribute can be queried and changed on the fly with the createtables() method.

NOTE: This is not yet implemented. For the moment, tables are NOT automatically created, regardless of the value of this attribute.


OBJECT METHODS

select($where)
Selects objects from the database using the SQL where clause supplied in $where.

  $database->select("where $key = $value");

dbhandle()
Returns the handle to the database connection. You could use this to execute arbitrary SQL queries on the database.

  $handle = $database->dbhandle()


BUGS

  • Error checking needs work.


SEE ALSO

Persistence::Object::Postgres(3), Data::Dumper(3), Persistence::Object::Simple(3), perlobj(1), perlbot(1), perltoot(1).


AUTHOR

Persistence::Database::SQL is Copyright (c) 2000 Ashish Gulhati <hash@netropolis.org>. All Rights Reserved.


ACKNOWLEDGEMENTS

Thanks to Barkha for inspiration, laughs and all 'round good times; to Vipul for Persistence::Object::Simple, the constant use and abuse of which resulted in the writing of this module; and of-course, to Larry Wall, Richard Stallman, and Linus Torvalds.


LICENSE

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

It would be nice if you would mail your patches to me, and I would love to hear about projects that make use of this module.


DISCLAIMER

This is free software. If it breaks, you own both parts.

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