4.2 KiB
Grouping lists of records
The [api:SS_List] class is designed to return a flat list of records. These lists can get quite long, and hard to present on a single list. Pagination is one way to solve this problem, by splitting up the list into multiple pages.
In this howto, we present an alternative to pagination:
Grouping a list by various criteria, through the [api:GroupedList] class.
This class is a [api:SS_ListDecorator], which means it wraps around a list,
adding new functionality.
It provides a groupBy() method, which takes a field name, and breaks up the managed list
into a number of arrays, where each array contains only objects with the same value of that field.
Similarly, the 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:SS_List] 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 {
private static $db = array(
'Title' => 'Text'
);
/**
* 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 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 GroupedList
*/
public function getGroupedModules() {
return GroupedList::create(Module::get()->sort('Title'));
}
}
The final step is to render this into a template. The 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>
<% loop $GroupedModules.GroupedBy(TitleFirstLetter) %>
<h3>$TitleFirstLetter</h3>
<ul>
<% loop $Children %>
<li>$Title</li>
<% end_loop %>
</ul>
<% end_loop %>
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:GroupedList->GroupedBy()] call.
We're reusing our example Module object,
but grouping by its built-in Created property instead,
which is automatically set when the record is first written to the database.
This will have a method which returns the month it was posted in:
:::php
class Module extends DataObject {
// ...
/**
* Returns the month name this news item was posted in.
* @return string
*/
public function getMonthCreated() {
return date('F', strtotime($this->Created));
}
}
The next step is to create a method that will return all records that exist,
sorted by month name from January to December. This can be accomplshed by sorting by the Created field:
:::php
class Page extends SiteTree {
// ...
/**
* Returns all news items, sorted by the month they were posted
* @return GroupedList
*/
public function getGroupedModulesByDate() {
return GroupedList::create(Module::get()->sort('Created'));
}
}
The final step is the render this into the template using the [api:GroupedList->GroupedBy()] method.
:::ss
// Modules list grouped by the Month Posted
<h2>Modules</h2>
<% loop $GroupedModulesByDate.GroupedBy(MonthCreated) %>
<h3>$MonthCreated</h3>
<ul>
<% loop $Children %>
<li>$Title ($Created.Nice)</li>
<% end_loop %>
</ul>
<% end_loop %>