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https://github.com/silverstripe/silverstripe-framework
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159 lines
4.8 KiB
Markdown
159 lines
4.8 KiB
Markdown
# Grouping lists of records
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The [SS_List](api:SilverStripe\ORM\SS_List) class is designed to return a flat list of records.
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These lists can get quite long, and hard to present on a single list.
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[Pagination](/developer_guides/templates/how_tos/pagination) is one way to solve this problem,
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by splitting up the list into multiple pages.
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In this howto, we present an alternative to pagination:
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Grouping a list by various criteria, through the [GroupedList](api:SilverStripe\ORM\GroupedList) class.
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This class is a [ListDecorator](api:SilverStripe\ORM\ListDecorator), which means it wraps around a list,
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adding new functionality.
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It provides a `groupBy()` method, which takes a field name, and breaks up the managed list
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into a number of arrays, where each array contains only objects with the same value of that field.
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Similarly, the `GroupedBy()` method builds on this and returns the same data in a template-friendly format.
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## Grouping Sets By First Letter
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This example deals with breaking up a [SS_List](api:SilverStripe\ORM\SS_List) into sub-headings by the first letter.
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Let's say you have a set of Module objects, each representing a SilverStripe module, and you want to output a list of
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these in alphabetical order, with each letter as a heading; something like the following list:
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* B
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* Blog
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* C
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* CMS Workflow
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* Custom Translations
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* D
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* Database Plumber
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* ...
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The first step is to set up the basic data model,
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along with a method that returns the first letter of the title. This
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will be used both for grouping and for the title in the template.
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```php
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use SilverStripe\ORM\DataObject;
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class Module extends DataObject
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{
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private static $db = [
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'Title' => 'Text'
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];
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/**
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* Returns the first letter of the module title, used for grouping.
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* @return string
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*/
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public function getTitleFirstLetter()
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{
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return $this->Title[0];
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}
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}
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```
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The next step is to create a method or variable that will contain/return all the objects,
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sorted by title. For this example this will be a method on the `Page` class.
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```php
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use SilverStripe\CMS\Model\SiteTree;
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use SilverStripe\ORM\GroupedList;
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class Page extends SiteTree
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{
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/**
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* Returns all modules, sorted by their title.
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* @return GroupedList
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*/
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public function getGroupedModules()
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{
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return GroupedList::create(Module::get()->sort('Title'));
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}
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}
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```
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The final step is to render this into a template. The `GroupedBy()` method breaks up the set into
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a number of sets, grouped by the field that is passed as the parameter.
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In this case, the `getTitleFirstLetter()` method defined earlier is used to break them up.
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```ss
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<%-- Modules list grouped by TitleFirstLetter --%>
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<h2>Modules</h2>
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<% loop $GroupedModules.GroupedBy(TitleFirstLetter) %>
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<h3>$TitleFirstLetter</h3>
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<ul>
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<% loop $Children %>
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<li>$Title</li>
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<% end_loop %>
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</ul>
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<% end_loop %>
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```
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## Grouping Sets By Month
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Grouping a set by month is a very similar process.
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The only difference would be to sort the records by month name, and
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then create a method on the DataObject that returns the month name,
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and pass that to the [GroupedList::GroupedBy()](api:SilverStripe\ORM\GroupedList::GroupedBy()) call.
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We're reusing our example `Module` object,
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but grouping by its built-in `Created` property instead,
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which is automatically set when the record is first written to the database.
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This will have a method which returns the month it was posted in:
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```php
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use SilverStripe\ORM\DataObject;
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class Module extends DataObject
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{
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/**
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* Returns the month name this news item was posted in.
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* @return string
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*/
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public function getMonthCreated()
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{
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return date('F', strtotime($this->Created));
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}
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}
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```
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The next step is to create a method that will return all records that exist,
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sorted by month name from January to December. This can be accomplshed by sorting by the `Created` field:
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```php
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use SilverStripe\CMS\Model\SiteTree;
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use SilverStripe\ORM\GroupedList;
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class Page extends SiteTree
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{
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/**
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* Returns all news items, sorted by the month they were posted
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* @return GroupedList
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*/
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public function getGroupedModulesByDate()
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{
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return GroupedList::create(Module::get()->sort('Created'));
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}
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}
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```
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The final step is the render this into the template using the [GroupedList::GroupedBy()](api:SilverStripe\ORM\GroupedList::GroupedBy()) method.
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```ss
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// Modules list grouped by the Month Posted
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<h2>Modules</h2>
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<% loop $GroupedModulesByDate.GroupedBy(MonthCreated) %>
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<h3>$MonthCreated</h3>
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<ul>
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<% loop $Children %>
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<li>$Title ($Created.Nice)</li>
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<% end_loop %>
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</ul>
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<% end_loop %>
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```
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## Related
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* [Howto: "Pagination"](/developer_guides/templates/how_tos/pagination)
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