This class represents a set of database objects, such as the results of a query. It is the base for all datamodel-related querying. It implements the Iterator interface introduced in PHP5.

Relations (has_many/many_many) are described in ComponentSet, a subclass of DataObjectSet.

$mySet->Count();

$myFirstDataObject = $mySet->First();
$myLastDataObject = $mySet->Last();

$mySpecialDataObjects = $mySet->find('Status', 'special');
$startingFromTen = $mySet->getOffset(10);
$tenToTwenty = $mySet->getRange(10, 10);

$myIDArray = $mySet->column('ID');

You can group a set by a specific column. Consider using SQLQuery with a GROUP BY statement for enhanced performance.

$groupedSet = $mySet->groupBy('Lastname');

Sort a set by a specific column.

$mySet->sort('Lastname'); //ascending
$mySet->sort('Lastname', 'DESC'); //descending

This works on the object itself, so do NOT do something like this:

$sortedSet = $mySet->sort('Lastname'); //ascending

$myFirstSet->merge($mySecondSet);
// $myFirstSet now contains all combined values

When using DropdownField and its numerous subclasses to select a value from a set, you can easily map the records to a compatible array:

$map = $mySet->toDropDownMap('ID', 'Title');
$dropdownField = new DropdownField('myField', 'my label', $map);

$myArray = $mySet->toArray();

Use buildNestedUL to return a nested unordered list out of a “chain” of DataObject-relations.

It is good practice to check for empty sets before doing any iteration.

$mySet = DataObject::get('Players');
if($mySet->exists()) foreach($mySet as $player)
// ...

DataObjects have native support for dealing with pagination. See setPageLimits, setPageLength, etc.

Complete pagination documentation

Click here for the API documentation.