4.0 KiB
Grouping Data Object Sets
The [api:DataObjectSet] class has a number of methods useful for grouping objects by fields. Together with sorting this can be used to break up long lists of data into more manageable sub-sections.
The [api:DataObjectSet->groupBy()] method takes a field name as the single argument, and breaks the set up into a number of arrays, where each array contains only objects with the same value of that field. The [api:DataObjectSet->GroupedBy()] method builds on this and returns the same data in a template-friendly format.
Grouping Sets By First Letter
This example deals with breaking up a [api:DataObjectSet] into sub-headings by the first letter.
Let's say you have a set of Module objects, each representing a SilverStripe module, and you want to output a list of these in alphabetical order, with each letter as a heading; something like the following list:
* B
* Blog
* C
* CMS Workflow
* Custom Translations
* D
* Database Plumber
* ...
The first step is to set up the basic data model, along with a method that returns the first letter of the title. This will be used both for grouping and for the title in the template.
:::php
class Module extends DataObject {
public static $db = array(
'Title' => 'Varchar(255)'
);
// ...
/**
* Returns the first letter of the module title, used for grouping.
*
* @return string
*/
public function getTitleFirstLetter() {
return $this->Title[0];
}
}
The next step is to create a method or variable that will contain/return all the Module objects, sorted by title. For this example this will be a method on the Page class.
:::php
class Page extends SiteTree {
// ...
/**
* Returns all modules, sorted by their title.
*
* @return DataObjectSet
*/
public function getModules() {
return DataObject::get('Module', null, '"Title"');
}
}
The final step is to render this into a template. The [api:DataObjectSet->GroupedBy()] method breaks up the set into a number of sets, grouped by the field that is passed as the parameter. In this case, the getTitleFirstLetter method defined earlier is used to break them up.
:::ss
// Modules list grouped by TitleFirstLetter
<h2>Modules</h2>
<% control Modules.GroupedBy(TitleFirstLetter) %>
<h3>$TitleFirstLetter</h3>
<ul>
<% control Children %>
<li>$Title</li>
<% end_control %>
</ul>
<% end_control %>
Grouping Sets By Month
Grouping a set by month is a very similar process. The only difference would be to sort the records by month name, and then create a method on the DataObject that returns the month name, and pass that to the [api:DataObjectSet->GroupedBy()] call.
Again, the first step is to create a method on the class in question that will be displayed in a list. For this example, a [api:DataObject] called NewsItem will be used. This will have a method which returns the month it was posted in:
:::php
class NewsItem extends DataObject {
public static $db = array(
'Title' => 'Varchar(255)',
'Date' => 'Date'
);
// ...
/**
* Returns the month name this news item was posted in.
*
* @return string
*/
public function getMonthPosted() {
return date('F', strtotime($this->Date));
}
}
The next step is to create a method that will return all the News records that exist, sorted by month name from January to December. This can be accomplshed by sorting by the Date field:
:::php
class Page extends SiteTree {
/**
* Returns all news items, sorted by the month they were posted
*
* @return DataObjectSet
*/
public function getNewsItems() {
return DataObject::get('NewsItem', null, '"Date"');
}
}
The final step is the render this into the template using the [api:DataObjectSet->GroupedBy()] method.
:::ss
// Modules list grouped by the Month Posted
<h2>Modules</h2>
<% control NewsItems.GroupedBy(MonthPosted) %>
<h3>$MonthPosted</h3>
<ul>
<% control Children %>
<li>$Title ($Date.Nice)</li>
<% end_control %>
</ul>
<% end_control %>