silverstripe-framework/docs/en/tutorials/5-dataobject-relationship-management.md

# Tutorial 5 - Dataobject Relationship Management

## Overview

In the [second tutorial](2-extending-a-basic-site) we have learned how to add extrafields to a page type thanks
to the *$db* array and how to add an image using the *$has_one* array and so create a relationship between a table and
the *Image* table by storing the id of the respective *Image* in the first table. This tutorial explores all this
relations between [DataObjects](/topics/datamodel#relations) and the way to manage them easily.

<div class="notice" markdown='1'>
	I'm using the default tutorial theme in the following examples so the templates may vary or you may need to change
	the template code in this example to fit your theme
</div>

## What are we working towards?

To simulate these relations between objects, we are going to simulate the management via the CMS of the **[Google Summer
Of Code 2007](http://www.silverstripe.com/google-summer-of-code-2007-we-are-in/)** that SilverStripe was part of.

To do this, we are gonna use the following objects :

*  Project : Project on SilverStripe system for the GSOC 
*  Student : Student involved in the project
*  Mentor : SilverStripe developer
*  Module : Module used for the project


This is a table which sums up the relations between them :
 | Project             | Student             | Mentor        | Modules          |                           
 | -------             | -------             | ------        | ------------------                           
 | i18n Multi-Language | Bernat Foj Capell   | Ingo Schommer | Cms, Framework, i18n, Translation              | 
 | Image Manipulation  | Mateusz Ujma        | Sam Minnee    | Cms, Framework, ImageManipulation              | 
 | Google Maps         | Ofir Picazo Navarro | Hayden Smith  | Cms, Framework, Maps                           | 
 | Mashups             | Lakshan Perera      | Matt Peel     | Cms, Framework, MashUps                        | 
 | Multiple Databases  | Philipp Krenn       | Brian Calhoun | Cms, Framework, MultipleDatabases              | 
 | Reporting           | Quin Hoxie          | Sam Minnee    | Cms, Framework, Reporting                      | 
 | Security & OpenID   | Markus Lanthaler    | Hayden Smith  | Cms, Framework, auth_openid                    | 
 | SEO                 | Will Scott          | Brian Calhoun | Cms, Framework, googleadwords, googleanalytics | 
 | Usability           | Elijah Lofgren      | Sean Harvey   | Cms, Framework, UsabilityElijah                | 
 | Safari 3 Support    | Meg Risen           | Sean Harvey   | Cms, Framework, UsabilityMeg                   | 

## GSOC Projects

Before starting the relations management, we need to create a *ProjectsHolder* class where we will save the GSOC Project
pages.

*tutorial/code/ProjectsHolder.php*

	:::php
	<?php
	
	class ProjectsHolder extends Page {
	
		static $allowed_children = array( 'Project' );
	
	}
	
	class ProjectsHolder_Controller extends Page_Controller {
	
	}

## Project - Student relation

**A project can only be done by one student.**

**A student has only one project.**

This relation is called a **1-to-1** relation.

The first step is to create the student and project objects.

*tutorial/code/Student.php*

	:::php
	<?php
	
	class Student extends DataObject {
	
		static $db = array(
			'FirstName' => 'Text',
			'Lastname' => 'Text',
			'Nationality' => 'Text'
		);
	
		public function getCMSFields_forPopup() {
			$fields = new FieldList();
			
			$fields->push( new TextField( 'FirstName', 'First Name' ) );
			$fields->push( new TextField( 'Lastname' ) );
			$fields->push( new TextField( 'Nationality' ) );
			
			return $fields;
		}
	
	}


*tutorial/code/Project.php*

	:::php
	<?php
	
	class Project extends Page {
	
		static $has_one = array(
			'MyStudent' => 'Student'
		);
	
	}
	class Project_Controller extends Page_Controller {}

This code will create a relationship between the *Project* table and the *Student* table by storing the id of the
respective *Student* in the *Project* table.

The second step is to add the table in the method *getCMSFields* which will allow you to manage the *has_one* relation.

	:::php
	class Project extends Page {
	
		...
	
		public function getCMSFields() {
			$fields = parent::getCMSFields();
			
			$tablefield = new HasOneComplexTableField(
				$this,
				'MyStudent',
				'Student',
				array(
					'FirstName' => 'First Name',
					'Lastname' => 'Family Name',
					'Nationality' => 'Nationality'
				),
				'getCMSFields_forPopup'
			);
			$tablefield->setParentClass('Project');
			
			$fields->addFieldToTab( 'Root.Student', $tablefield );
			
			return $fields;
		}
	
	}

Let’s walk through the parameters of the *HasOneComplexTableField* constructor.

1.  **$this** : The first object concerned by the relation
2.  **'MyStudent'** : The name of the second object of the relation
3.  **'Student'** : The type of the second object of the relation
4.  **array(...)** : The fields of the second object which will be in the table
5.  **'getCMSFields_forPopup'** : The method which will be called to add, edit or only show a second object

You can also directly replace the last parameter by this code :

	:::php
	   new FieldList(
	      new TextField( 'FirstName', 'First Name' ),
	      new TextField( 'Lastname' ),
	      new TextField( 'Nationality' )
	   );


<div class="tip" markdown='1'>
	Don't forget to rebuild the database using *dev/build?flush=1* before you 
	proceed to the next part of this tutorial.
</div>

Now that we have created our *Project* page type and *Student* data object, let’s add some content.

Go into the CMS and create one *Project* page for each project listed [above](#what-are-we-working-towards) under a 
*ProjectsHolder* page named **GSOC Projects** for instance.

![tutorial:gsoc-project-creation.png](_images/gsoc-project-creation.jpg)

As you can see in the tab panel *Student*, the adding functionality is titled *Add Student*. However, if you want to
modify this title, you have to add this code in the *getCMSFields* method of the *Project* class :

	:::php
	$tablefield->setAddTitle( 'A Student' );


Select now one of the *Project* page that you have created, go in the tab panel *Student* and add all the students
listed [above](#what-are-we-working-towards) by clicking on the link **Add A Student** of your 
*HasOneComplexTableField* table.

![tutorial:gsoc-student-creation.png](_images/gsoc-student-creation.jpg)

After having added all the students, you will see that, in the tab panel *Student* of all the *Project* pages, the
*HasOneComplexTableField* tables have the same content.

For each *Project* page, you can now affect **one and only one** student to it ( see the
[list](#What_are_we_working_towards?) ).

![tutorial:gsoc-project-student-selection.png](_images/gsoc-project-student-selection.jpg)

You will also notice, that you have the possibility to **unselect** a student which will make your *Project* page
without any student affected to it.

**At the moment, the *HasOneComplexTableField* table doesn't manage totally the *1-to-1* relation because you can easily
select the same student for two ( or more ) differents *Project* pages which corresponds to a *1-to-many* relation.**

To use your *HasOneComplexTableField* table for a **1-to-1** relation, make this modification in the class *Project* :

	:::php
	class Project extends Page {
	
		...
	
		public function getCMSFields() {
		
			...
			
			$tablefield->setParentClass('Project');
			
			$tablefield->setOneToOne();
			
			$fields->addFieldToTab( 'Root.Content.Student', $tablefield );
			
			return $fields;
		}
	
	}

Now, you will notice that by checking a student in a *Project* page, you will be unable to select him again in any other
*Project* page which is the definition of a **1-to-1** relation.






## Student - Mentor relation

**A student has one mentor.**

**A mentor has several students.**

This relation is called a **1-to-many** relation.

The first step is to create the mentor object and set the relation with the *Student* data object.

*tutorial/code/Mentor.php*

	:::php
	<?php
	
	class Mentor extends Page {
	
		static $db = array(
			'FirstName' => 'Text',
			'Lastname' => 'Text',
			'Nationality' => 'Text'
		);
		
		static $has_many = array(
			'Students' => 'Student'
		);
		
		public function getCMSFields() {
			$fields = parent::getCMSFields();
			
			$fields->addFieldToTab( 'Root.Content', new TextField( 'FirstName' ) );
			$fields->addFieldToTab( 'Root.Content', new TextField( 'Lastname' ) );
			$fields->addFieldToTab( 'Root.Content', new TextField( 'Nationality' ) );
		
			return $fields;
		}
	
	}
	class Mentor_Controller extends Page_Controller {}

*tutorial/code/Student.php*

	:::php
	class Student extends DataObject {
	
		...
	
		static $has_one = array(
			'MyMentor' => 'Mentor'
		);
	
	}


This code will create a relationship between the *Student* table and the *Mentor* table by storing the id of the
respective *Mentor* in the *Student* table.

The second step is to add the table in the method *getCMSFields* which will allow you to manage the *has_many* relation.

*tutorial/code/Mentor.php*

	:::php
	class Mentor extends Page {
	
		...
	
		public function getCMSFields() {
			$fields = parent::getCMSFields();
		
			...
		
			$tablefield = new HasManyComplexTableField(
				$this,
				'Students',
				'Student',
				array(
					'FirstName' => 'FirstName',
					'Lastname' => 'Family Name',
					'Nationality' => 'Nationality'
				),
				'getCMSFields_forPopup'
			);
			$tablefield->setAddTitle( 'A Student' );
		
			$fields->addFieldToTab( 'Root.Students', $tablefield );
		
			return $fields;
		}
	
	}
	class Mentor_Controller extends Page_Controller {}

To know more about the parameters of the *HasManyComplexTableField* constructor, [check](#project_-_student_relation)
those of the *HasOneComplexTableField* constructor.

<div class="tip" markdown='1'>
	Don't forget to rebuild the database using *dev/build?flush=1* before you 
	proceed to the next part of this tutorial.
</div>

Now that we have created our *Mentor* page type, go into the CMS and create one *Mentor* page for each mentor listed
[above](#what-are-we-working-towards) under a simple *Page* named
**Mentors** for instance.

![tutorial:gsoc-mentor-creation.png](_images/gsoc-mentor-creation.jpg)

For each *Mentor* page, you can now affect **many** students created previously ( see the
[list](#What_are_we_working_towards?) ) by going in the tab panel *Students*.

![tutorial:gsoc-mentor-student-selection.png](_images/gsoc-mentor-student-selection.jpg)

You will also notice, that by checking a student in a *Mentor* page, you will be unable to select him again in any other
*Mentor* page which is the definition of a **1-to-many** relation.

As the *HasOneComplexTableField* table, you also have the possibility not to select any student which will make your
*Mentor* page without any student affected to it.










## Project - Module relation

**A project uses several modules.**

**A module is used by several projects.**

This relation is called a **many-to-many** relation.

The first step is to create the module object and set the relation with the *Project* page type.

*tutorial/code/Module.php*

	:::php
	<?php
	
	class Module extends DataObject {
	
	   static $db = array(
	      'Name' => 'Text'
	   );
	
	   static $belongs_many_many = array(
	      'Projects' => 'Project'
	   );
	
	   public function getCMSFields_forPopup() {
	      $fields = new FieldList();
	      $fields->push( new TextField( 'Name' ) );
	      return $fields;
	   }
	
	}

*tutorial/code/Project.php*

	:::php
	class Project extends Page {
	
	   ...
	
	   static $many_many = array(
	      'Modules' => 'Module'
	   );
	
	}


This code will create a relationship between the *Project* table and the *Module* table by storing the ids of the
respective *Project* and *Module* in a another table named **Project_Modules**.

The second step is to add the table in the method *getCMSFields* which will allow you to manage the *many_many*
relation.

	:::php
	class Project extends Page {
	
	   ...
	
	   public function getCMSFields() {
	      $fields = parent::getCMSFields();
	
	      ...
	
	      $modulesTablefield = new ManyManyComplexTableField(
	         $this,
	         'Modules',
	         'Module',
	         array(
		    'Name' => 'Name'
	         ),
	         'getCMSFields_forPopup'
	      );
	      $modulesTablefield->setAddTitle( 'A Module' );
	
	      $fields->addFieldToTab( 'Root.Modules', $modulesTablefield );
	
	      return $fields;
	   }
	
	}

To know more about the parameters of the *ManyManyComplexTableField* constructor,
[check](#project_-_student_relation) those of the *HasOneComplexTableField*
constructor.

<div class="tip" markdown='1'>
	Don't forget to rebuild the database using *dev/build?flush=1* before you 
	proceed to the next part of this tutorial.
</div>

Select now one of the *Project* page, go in the tab panel *Modules* and add all the modules listed
[above](#what-are-we-working-towards) by clicking on the link **Add A
Module** of your *ManyManyComplexTableField* table.

![tutorial:gsoc-module-creation.png](_images/gsoc-module-creation.jpg)

For each *Project* page, you can now affect **many** modules created previously ( see the
[list](#What_are_we_working_towards?) ) by going in the tab panel
*Modules*.

![tutorial:gsoc-project-module-selection.png](_images/gsoc-project-module-selection.jpg)

You will also notice, that you are able to select several times a *Module* on different *Project* pages which is the
definition of a **many-to-many** relation.

As the *HasOneComplexTableField* and *HasManyComplexTableField* table, you also have the possibility not to select any
module which will make your *Project* page without any module affected to it.





## Displaying the data on your website

Now that we have created all the *Page* and *DataObject* classes necessary and the relational tables to
manage the [relations](../topics/datamodel#relations) between them, we would like to see these relations on the website.

We will see in this section how to display all these relations but also how to create a template for a *DataObject*.

For every kind of *Page* or *DataObject*, you can access to their relations thanks to the **control** loop.

**1. GSOC Projects**

Let's start with the *ProjectsHolder* page created before. For this template, we are will display the same table than
[above](#what-are-we-working-towards).

![tutorial:gsoc-projects-table.png](_images/gsoc-projects-table.jpg)

*tutorial/templates/Layout/ProjectsHolder.ss*

	:::ss
	<% include Menu2 %>

	<div id="Content" class="typography">
		<% if Level(2) %>
	        <% include BreadCrumbs %>
	    <% end_if %>

		$Content

		<table>
	        <thead>
	            <tr>
	                <th>Project</th>
	                <th>Student</th>
	                <th>Mentor</th>
	                <th>Modules</th>
	            </tr>
	        </thead>
	        <tbody>
	            <% control Children %>
	                <tr>
	                    <td>$Title</td>
	                    <td>
	                        <% if MyStudent %>
	                            <% control MyStudent %>
	                                $FirstName $Lastname
	                            <% end_control %>
	                        <% else %>
	                            No Student
	                        <% end_if %>
	                    </td>
	                    <td>
	                        <% if MyStudent %>
	                            <% control MyStudent %>
	                                <% if MyMentor %>
	                                    <% control MyMentor %>
	                                        $FirstName $Lastname
	                                    <% end_control %>
	                                <% else %>
	                                    No Mentor
	                                <% end_if %>
	                            <% end_control %>
	                        <% else %>
	                            No Mentor
	                        <% end_if %>
	                    </td>
	                    <td>
	                        <% if Modules %>
	                            <% control Modules %>
	                                $Name &nbsp;
	                            <% end_control %>
	                        <% else %>
	                            No Modules
	                        <% end_if %>
	                    </td>
	                </tr>
	            <% end_control %>
	        </tbody>
	    </table>

		$Form

	</div>


<div class="notice" markdown='1'>
	If you are using the blackcandy template: You might want to move the `<% include Sidebar %>`
	(tutorial/templates/Includes/SideBar.ss) include in the *tutorial/templates/Layout/Page.ss* template above
	the typography div to get rid of the bullets
</div>


**2. Project**

We know now how to easily access and show [relations](../topics/datamodel#relations) between *DataObject* in a template.

We can now do the same for every *Project* page by creating its own template.

![tutorial:gsoc-project.png](_images/gsoc-project.jpg)

*tutorial/templates/Layout/Project.ss*

	:::ss
	<% include Menu2 %>

	<div id="Content" class="typography">
		<% if Level(2) %>
	        <% include BreadCrumbs %>
	    <% end_if %>

		$Content

		<% if MyStudent %>
	        <% control MyStudent %>
	            <p>First Name: <strong>$FirstName</strong></p>
	            <p>Lastname: <strong>$Lastname</strong></p>
	            <p>Nationality: <strong>$Nationality</strong></p>

	            <h3>Mentor</h3>

	            <% if MyMentor %>
	                <% control MyMentor %>
	                    <p>First Name: <strong>$FirstName</strong></p>
	                    <p>Lastname: <strong>$Lastname</strong></p>
	                    <p>Nationality: <strong>$Nationality</strong></p>
	                <% end_control %>
	            <% else %>
	                <p>This student doesn't have any mentor.</p>
	            <% end_if %>
	        <% end_control %>
	    <% else %>
	        <p>There is no any student working on this project.</p>
	    <% end_if %>

	    <h3>Modules</h3>

	    <% if Modules %>
	        <ul>
	            <% control Modules %>
	                <li>$Name</li>
	            <% end_control %>
	        </ul>
	    <% else %>
	        <p>This project has not used any modules.</p>
	    <% end_if %>

		$Form

	</div>


What we would like now is to create a special template for the *DataObject* *Student* and the *Page* *Mentor* which will
be used when we will call directly the variable in the *Project* template. In our case, we will use the same template
because these two classes have the same fields ( FirstName, Surname and Nationality ).

*tutorial/templates/Includes/GSOCPerson.ss*

	:::ss
	<p>First Name: <strong>$FirstName</strong></p>
	<p>Lastname: <strong>$Lastname</strong></p>
	<p>Nationality: <strong>$Nationality</strong></p>


Now the template is created, we need to establish the link between the *Student* and *Mentor* classes with their common
template.

To do so, add this code in the two classes.  This will create a control on each of those objects which can be called 
from templates either within a control block or dot notation.

*tutorial/code/Student.php, tutorial/code/Mentor.php*

	:::php
	public function PersonalInfo() {
		$template = 'GSOCPerson';
		return $this->renderWith( $template );
	}


We can now modify the *Project.ss* template.

	:::ss
	
	...
	
	<% if MyStudent %>
		$MyStudent.PersonalInfo
	
		<h3>Mentor</h3>
		
		<% control MyStudent %>
			<% if MyMentor %>
				$MyMentor.PersonalInfo
			<% else %>
				<p>This student doesn't have any mentor.</p>
			<% end_if %>
		<% end_control %>
	<% else %>
		<p>There is no any student working on this project.</p>
	<% end_if %>
	
	...

<div class="notice" markdown='1'>
	Remember to add `?flush=1` to the url when refreshing the project page or otherwise you will get a template error
</div>

In the *Project* template, it has been really easy to display the **1-to-1** relation with a *Student* object just by
calling the variable **$MyStudent**. This has been made possible thanks to the code below present in the *Project*
class.

	:::php
	static $has_one = array(
	    'MyStudent' => 'Student'
	);


However, in the *Student* class, there is no any code relating to the **1-to-1** relation with a *Project* *Page*. So
how to access it from a *Student* *DataObject* ?

**3. Mentor**

In this template, we are gonna try to access the *Project* details from a *Student* *DataObject*.

What we want to do is to access to the *Project* page in the same way than we have done for the other relations
**without modifying the relations between *Page* and *DataObject* and the database structure**.

![tutorial:gsoc-mentor.png](_images/gsoc-mentor.jpg)

To do so, we have to create a function in the *Student* class which will return the *Project* linked with it. Let's call
it *MyProject* for instance.

	:::php
	class Student extends DataObject {
	
		...
	
		public function MyProject() {
			return Project::get()->filter("MyStudentID", $this->ID);
		}
	
	}


We can now use this value in the same way that we have used the other relations.
That's how we can use this function in the *Mentor* template.

*tutorial/templates/Layout/Mentor.ss*

	:::ss
	<% include Menu2 %>

	<div id="Content" class="typography">
		<% include BreadCrumbs %>
		$Content

	    <h3>Personal Details</h3>

	    <p>First Name: <strong>$FirstName</strong></p>
	    <p>Lastname: <strong>$Lastname</strong></p>
	    <p>Nationality: <strong>$Nationality</strong></p>

	    <h3>Students</h3>

	    <% if Students %>
	        <table>
	            <thead>
	                <tr>
	                    <th>Student</th>
	                    <th>Project</th>
	                </tr>
	            </thead>
	            <tbody>
	                <% control Students %>
	                    <tr>
	                        <td>$FirstName $Lastname</td>
	                        <td>
	                            <% if MyProject %>
	                                <% control MyProject %>
	                                    $Title
	                                <% end_control %>
	                            <% else %>
	                                No Project
	                            <% end_if %>
	                        </td>
	                    </tr>
	                <% end_control %>
	            </tbody>
	        </table>
	    <% else %>
	        <p>There is no any student working with this mentor.</p>
	    <% end_if %>

	    $Form
	</div>


## Summary

This tutorial has demonstrated how easy it is to manage all the type of relations between *DataObject* objects in the
CMS and how to display them on the website.


## Download the code

Download all the [code](http://doc.silverstripe.org/framework/docs/en/tutorials/_images/tutorial5-completecode.zip) for this tutorial.

You can also download the [code](http://doc.silverstripe.org/framework/docs/en/tutorials/_images/tutorial5-completecode-blackcandy.zip) for use in the blackcandy template.