EXT: Bidirectional M-M relations¶

The problem at hand¶

It has bothered me for some time that MM-relations in TYPO3s backend were only singledirectional. To explain what I mean by that, take this example:

You have two tables, tx_myext_table1 and tx_myext_table2 . In tx_myext_table1 you have configured a field of type “select”. The item array of this select field is filled with records from t x_myext_table2 by using an M-M relation. For this purpose a third “join”-table tx_myext_table1_table2_mm is used.

In order to find any relations TYPO3 expects the tx_myext_table1_table2_mm to contain the following fields:

uid_local - this points to the uid of the local table (tx_myext_table1). uid_foreign – this points to the uid of the foreign table (tx_myext_table2).

So far everything is good. You can view, edit and delete relations between the two tables - but only from the local table´s point of view . Now, what if you wanted to create a “select” field in the tx_myext_table2 which was populated with records from the tx_myext_table1 using the same “join” table ( tx_myext_table1_table2_mm) ? The short answer to that question is: You can't.

To give you a real world example, take a look at the tt_news extension. You can open a single tt_news record and assign it to one or more categories. But you can't open a category and select which tt_news records should be assigned to it.

This is were this extension comes in. It allows you to create “select” and “group” fields that uses the uid_local field in the “join” table to lookup records in the foreign table.

Addition to Core API's (section 4.2.9 ['columns'][fieldname]['config'] / TYPE: "select")¶

'config' => Array(
    'type' => 'select',
    'foreign_table' => 'tx_myext_table1',
    'MM' => 'tx_myext_table1_table2_mm | foreign',
    'maxitems' => 100
)

Addition to Core API's (section 4.2.10 ['columns'][fieldname]['config'] / TYPE: "group")¶

'config' => Array(
    'type' => 'group',
    'allowed' => 'tx_myext_table1',
    'MM' => 'tx_myext_table1_table2_mm | foreign',
    'maxitems' => 100
)

#
# Example MM table for database relations
#

CREATE TABLE example_db_mm (
  uid_local int(11) DEFAULT '0' NOT NULL,
  uid_foreign int(11) DEFAULT '0' NOT NULL,
  tablenames varchar(30) DEFAULT '' NOT NULL,
  sorting int(11) DEFAULT '0' NOT NULL,
  KEY uid_local (uid_local),
  KEY uid_foreign (uid_foreign)
) TYPE=MyISAM;

#
# Example MM table for file attachments
#

CREATE TABLE example_files_mm (
  uid_local int(11) DEFAULT '0' NOT NULL,
  uid_foreign varchar(60) DEFAULT '' NOT NULL,
  sorting int(11) DEFAULT '0' NOT NULL,
  KEY uid_local (uid_local),
  KEY uid_foreign (uid_foreign)
) TYPE=MyISAM;

Example: Adding a bidirectional field in tt_news¶

In this section I will go through an example of how to use bidirectional M-M relations. This example extends the tt_news extension by adding a bidirectional field to the tt_news_cat table. NOTE: An implementation of this example is uploaded to the TER in the bidirectional_example extension.

Creating the field in the database¶

We start by creating the field in the database:

#
# Table structure for table 'tt_news_cat'
#
CREATE TABLE tt_news_cat (
        tx_bidirectionalexample_tt_news int(11) DEFAULT '0' NOT NULL
);

Konfiguring the field¶

Next, we configure the field and adds it to the $TCA:

 0: <?php
 1: if (!defined ('TYPO3_MODE'))     die ('Access denied.');
 2: $tempColumns = Array (
 3:     "tx_bidirectionalexample_tt_news" => Array (
 4:         "exclude" => 1,
 5:         "label" => "News in this category",
 6:         "config" => Array (
 7:             "type" => "select",
 8:             "foreign_table" => "tt_news",
 9:             "foreign_table_where" => "ORDER BY tt_news.crdate",
10:             "size" => 10,
11:             "minitems" => 0,
12:             "maxitems" => 100,
13:             "MM" => "tt_news_cat_mm | foreign",
14:         )
15:     ),
16: );
17: t3lib_div::loadTCA("tt_news_cat");
18: t3lib_extMgm::addTCAcolumns("tt_news_cat",$tempColumns,1);
19: t3lib_extMgm::addToAllTCAtypes("tt_news_cat","tx_bidirectionalexample_tt_news;;;;1-1-1");
20: ?>

Notice the syntax of line 13

XCLASS'ing¶

In order to achieve it's goal this extension XCLASSes “t3lib_loadDBGroup”. In my opinion XCLASS'ing is a very bad way of extending the functionality of TYPO3 and most of the time I only use the technique for “user_*” extensions (extensions that are not going to be made public). Therefore I advise you only to use this extension if you really need the functionality of bidirectional relations.

Sorting¶

There are some issues with the sorting of items which have still to be cleared out.

List module¶

Values from bidirectional fields may not display correctly in the List module's “extended mode”.