Automatic Table Linking

PEAR Handbuch
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Automating the collection of related data

When designing a database, often some tables are related to others - a membership table would contain a reference to a person's id and the group id that they are a member of. Using the Link methods, you can automatically fetch objects into the parents variables.

The Automated method of doing this is heavily dependent on naming columns relating to databases, for example in the membership described above, you would have to have a column called person_id, group_id for the automated Link methods to understand which table to fetch the data from. The principle is TABLENAME_ANYTHING, and it will always attempt to find primary keys that match the value of field, the getLinks() methods will auto load the related object into $object->_tablename_anything

The other way of using getLink() is to use it with the second parameter which is the table name of the related table, it will then query the primary key on that table to see if it matches the value of the requested row. In this method however the getLinks() method will not work, as it will not know the related table names.

Using link ini files for table links

DB_DataObject Version 0.3 introduced the ability to create link ini files so you can map rows to other database columns using an ini file this ini file should have the name databasename.links.ini, and be placed in the same folder as the databasename.ini file that is created automatically by createTables.php

The Ini file contains a section for each table, then the row that is linked equal to the table and row that it should locate the row from. If you use a 'full stop' in the key (link from column), getLinks() will look up in the table with the row name matching the string to the left of the 'full stop', and replace the 'full stop' with and underscore and assign the object variable to that name.
Beispiel 1. An example databasename.links.ini file
; for table person [person] ; link value of eycolor to table colors, match name column eyecolor = colors:name ; link value of owner to table grp, match id column owner = grp:id ; link value of picture to table attachments, match id column picture = attachments:id ; for a sales example with multiple links of a single column [sales] ; for autoloading the car object into $sales->_car_id car_id = car:id ; for autoloading the part number object into $sales->_car_id_partnum car_id.partnum = part_numbers:car_id

::getLink()

Gets the Related Row Object from the Related Table

::getLink (string Row [, string Table [, string Key]])

This would execute the following SQL statements, and fetch the data
Beispiel 3. Resulting SQL
SELECT * FROM person WHERE id=12 SELECT * FROM group WHERE id=3 SELECT * FROM hair WHERE id=4

::getLinks()

Loads all the related Objects

::getLinks ()

This would execute the following SQL statement, and fetch the data
Beispiel 6. Resulting SQL
SELECT * FROM person WHERE id=1079 SELECT * FROM convention WHERE id=1
And output the following data
Beispiel 7. Resulting Output
Object:dataobjects_person Object ( [_DB_DataObject_version] => 1.0 [__table] => person [_database_dsn] => [_database_dsn_md5] => 3974043abbccdd6412fb156a1d10b98377 [_database] => testing [_condition] => [_group_by] => [_order_by] => [_limit] => [_data_select] => * [_link_loaded] => 1 [_lastError] => pear_error Object ( [error_message_prefix] => [mode] => 1 [level] => 1024 [code] => -3 [message] => getLink:Could not find class for row last_modified, table last [userinfo] => [callback] => ) [id] => 1079 [N] => 1 [_DB_resultid] => 2 [first_name] => Tim [last_name] => White [middle_name] => [badge_number] => 123 [street] => 334411 N Washington [city] => Texas [state] => CO [zip] => 12345 [phone] => 343412323232 [reg_type] => Staff [judge] => [staff] => CHECKED [volunteer] => [rpga_number] => 1232323 [total_fee] => 0.00 [email_address] => tim@example.com [country] => USA [convention_id] => 1 [last_modified] => 20020711084539 [_first_name] => [_last_name] => [_middle_name] => [_badge_number] => [_reg_type] => [_rpga_number] => [_total_fee] => [_email_address] => [_convention_id] => dataobjects_convention Object ( [_DB_DataObject_version] => 1.0 [__table] => convention [_database_dsn] => [_database_dsn_md5] => 3974043abbcc86412fb156a1d10b98377 [_database] => testing [_condition] => [_group_by] => [_order_by] => [_limit] => [_data_select] => * [_link_loaded] => [_lastError] => [id] => 1 [N] => 1 [_DB_resultid] => 3 [name] => ABCD XYZ [sponsor_organization] => some sponser [rpga_convention_code] => ABCD_XYZ [web_site_url] => http://example.com [last_modified] => 20020703143828 ) [_last_modified] => )

In the example above, alot of the columns have '_' underscores in and do not relate to tables, DB_DataObject will only flag it as an error in $object->_lastError.

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