Dynamically Generating Dropdown Lists

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13 October 2010 | Aram Balakjian | CMS, DataObjects, Forms | Supports v2.4, v2.3

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This post title may look familiar, but it has in fact been completely re-written with lots of new code! When using dropdown menus, you will often want to dynamically generate the options, usually to a list of DataObjects or Pages for the user to choose from. This tutorial explores the options at your disposal when it comes to creating dynamic dropdowns in the SilverStripe.

From Enum Values

Alternatively you can generate the list from a set of Enum values defined in your $db array like so:

	"Options" => "Enum('Default, Option1, Option2, Option3', 'Default')"

Then use this syntax when adding your form field to the getCMSFields() function:

$fields->addFieldToTab(
	"Root.Content.Main",
	new DropdownField(
		'Options',
		'Choose an option', 
		$this->dbObject('Options')->enumValues())
);

From DataObjects

The Quick way

If you want to create a drop down list (or option set) dynamically, for example from a set of pages or DataObjects, you can use the DataObject::get() call along with the function toDropdownMap() to generate it like so:

new DropdownField(
	'DataObjectID',
	'Please choose an object',
	Dataobject::get("MyObject")->map("ID", "Title", "Please Select")
);

We use the map() function to generate a key => Value array, with the ID as the Key which is what will be saved) and the Title field as the value (which is what will be displayed). The downside to this method is that if there are no MyObject objects you will get a big far error.

The Longer (more stable) way

In order to prevent the error above you can instead create a function which will either return the mapped values or an array containing a 'None Found' type message. That function might look something like this:

function getMyObjectOptions()
{
	if($Pages = DataObject::get('MyObject'))
	{
	return $Pages->map('ID', 'Title', 'Please Select');
	}
	else
	{
	return array('No Objects found');
	}
}

Then in your Dropdown definition you just add $this->getMyObjectOptions() as the $Source argument:

new DropdownField(
	'DataObjectID',
	'Please choose an object',
	$this->getMyObjectOptions()
);

Adding custom 'Summary' values

Let's say you wanted your dropdown options to say something like 'MyObjectTitle running on 23/3/2010'. Well that is pretty simple actually, all you need to do is create a function inside MyObject which returns the string that you want. So for example let's assume that the MyObject DataObject has a field Title and a field Date, here is the function you would add to MyObject.php

function DropdownSummary()
{
	$String = $this->Title . ' running on ' $this->dbObject('Date')->Nice();
		
	return $String;
}

Then in our getMyObjectOptions() function we simply specify DropdownSummary in the map() function instead of Title

function getMyObjectOptions()
{
	if($Pages = DataObject::get('MyObject'))
	{
	return $Pages->map('ID', 'DropdownSummary', 'Please Select');
	}
	else
	{
	return array('No Objects found');
	}
}