# 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

<% control Modules.GroupedBy(TitleFirstLetter) %>

$TitleFirstLetter

<% 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

<% control NewsItems.GroupedBy(MonthPosted) %>

$MonthPosted

<% end_control %>