Introduction to the data model and ORM#

Silverstripe uses an object-relational mapping to represent its information.

• Each database table maps to a PHP class.
• Each database row maps to a PHP object.
• Each database column maps to a property on a PHP object.

All data tables in Silverstripe CMS are defined as subclasses of DataObject. The DataObject class represents a single row in a database table, following the "Active Record" design pattern. Database Columns are defined as Data Types in the static $db variable along with any relationships defined as $has_one, $has_many, $many_many properties on the class.

Let's look at a simple example:

// app/src/Model/Player.php
namespace App\Model;

use SilverStripe\ORM\DataObject;

class Player extends DataObject
{
    private static $db = [
        'PlayerNumber' => 'Int',
        'FirstName' => 'Varchar(255)',
        'LastName' => 'Text',
        'Birthday' => 'Date',
    ];
}

This Player class definition will create a database table Player with columns for PlayerNumber, FirstName and so on. After writing this class, we need to regenerate the database schema.

Generating the database schema#

After adding, modifying or removing DataObject subclasses, make sure to rebuild your Silverstripe CMS database. The database schema is generated automatically by visiting the URL http://www.yoursite.com/dev/build while authenticated as an administrator.

This script will analyze the existing schema, compare it to what's required by your data classes, and alter the schema as required.

It will perform the following changes:

• Create any missing tables
• Create any missing fields
• Create any missing indexes
• Alter the field type of any existing fields
• Rename any obsolete tables that it previously created to _obsolete_(tablename)

It won't do any of the following

• Delete tables
• Delete fields
• Rename any tables that it doesn't recognize. This allows other applications to coexist in the same database, as long as their table names don't match a Silverstripe CMS data class.

When rebuilding the database schema through the ClassLoader the following additional properties are automatically set on the DataObject.

• ID: Primary Key. This will use the database's built-in auto-numbering system on the base table, and apply the same ID to all subclass tables.
• ClassName: An enumeration listing this data-class and all of its subclasses.
• Created: A date/time field set to the creation date of this record
• LastEdited: A date/time field set to the date this record was last edited through write()

// app/src/Model/Player.php
namespace App\Model;

use SilverStripe\ORM\DataObject;

class Player extends DataObject
{
    private static string $table_name = 'Player';

    private static $db = [
        'PlayerNumber' => 'Int',
        'FirstName' => 'Varchar(255)',
        'LastName' => 'Text',
        'Birthday' => 'Date',
    ];
}

Generates the following SQL.

CREATE TABLE `Player` (
    `ID` int(11) NOT NULL AUTO_INCREMENT,
    `ClassName` enum('Player') DEFAULT 'Player',
    `LastEdited` datetime DEFAULT NULL,
    `Created` datetime DEFAULT NULL,
    `PlayerNumber` int(11) NOT NULL DEFAULT '0',
    `FirstName` varchar(255) DEFAULT NULL,
    `LastName` mediumtext,
    `Birthday` datetime DEFAULT NULL,

    PRIMARY KEY (`ID`),
    KEY `ClassName` (`ClassName`)
);

Creating data records#

A new instance of a DataObject can be created using the new syntax.

$player = new Player();

Or, a better way is to use the create method.

$player = Player::create();

Database columns and properties can be set as class properties on the object. The Silverstripe CMS ORM handles the saving of the values through a custom __set() method.

$player->FirstName = 'Sam';
$player->PlayerNumber = 07;

To save the DataObject to the database, use the write() method. The first time write() is called, an ID will be set.

$player->write();

For convenience, the write() method returns the record's ID. This is particularly useful when creating new records.

$player = Player::create();
$id = $player->write();

Querying data#

With the Player class defined we can query our data using the ORM or Object-Relational Model. The ORM provides shortcuts and methods for fetching, sorting and filtering data from our database.

$players = Player::get();
// returns a `DataList` containing all the `Player` objects.

$player = Player::get()->byID(2);
// returns a single `Player` object instance that has the ID of 2.

echo $player->ID;
// returns the players 'ID' column value

echo $player->dbObject('LastEdited')->Ago();
// calls the `Ago` method on the `LastEdited` property.

The ORM uses a "fluent" syntax, where you specify a query by chaining together different methods. Two common methods are filter() and sort():

$members = Player::get()->filter([
    'FirstName' => 'Sam',
])->sort('Surname');

// returns a `DataList` containing all the `Player` records that have the `FirstName` of 'Sam'

Lazy loading#

The ORM doesn't actually execute the SQLSelect until you iterate on the result with a foreach() or <% loop %>.

It's smart enough to generate a single efficient query at the last moment in time without needing to post-process the result set in PHP. In MySQL the query generated by the ORM may look something like this

$players = Player::get()->filter([
    'FirstName' => 'Sam',
]);

$players = $players->sort('Surname');

// executes the following single query
// SELECT * FROM Player WHERE FirstName = 'Sam' ORDER BY Surname

This also means that getting the count of a list of objects will be done with a single, efficient query.

$players = Player::get()->filter([
    'FirstName' => 'Sam',
])->sort('Surname');

// This will create an single SELECT COUNT query
// SELECT COUNT(*) FROM Player WHERE FirstName = 'Sam'
echo $players->Count();

Looping over a list of objects#

get() returns a DataList instance. You can loop over DataList instances in both PHP and templates.

$players = Player::get();

foreach ($players as $player) {
    echo $player->FirstName;
}

Notice that we can step into the loop safely without having to check if $players exists. The get() call is robust, and will at worst return an empty DataList object. If you do want to check if the query returned any records, you can use the exists() method, e.g.

$players = Player::get();

if ($players->exists()) {
    // do something here
}

See the Lists documentation for more information on dealing with SS_List instances.

Returning a single DataObject#

There are a couple of ways of getting a single DataObject from the ORM. If you know the ID number of the object, you can use byID($id):

$player = Player::get()->byID(5);

get() returns a DataList instance. You can use operations on that to get back a single record.

$players = Player::get();

$first = $players->first();
$last = $players->last();

Sorting#

If you would like to sort the list by FirstName in an ascending way (from A to Z).

 // Sort can either be Ascending (ASC) or Descending (DESC)
$players = Player::get()->sort('FirstName', 'ASC');

 // Ascending is implied
$players = Player::get()->sort('FirstName');

To reverse the sort

$players = Player::get()->sort('FirstName', 'DESC');

// or..
$players = Player::get()->sort('FirstName', 'ASC')->reverse();

However you might have several entries with the same FirstName and would like to sort them by FirstName and LastName

$players = Players::get()->sort([
    'FirstName' => 'ASC',
    'LastName' => 'ASC',
]);

You can also sort randomly. Using the DB class, you can get the random sort method per database type.

$random = DB::get_conn()->random();
$players = Player::get()->sort($random);

Filtering results#

The filter() method filters the list of objects that gets returned.

$players = Player::get()->filter([
    'FirstName' => 'Sam',
]);

Each element of the array specifies a filter. You can specify as many filters as you like, and they all must be true for the record to be included in the result.

The key in the filter corresponds to the field that you want to filter and the value in the filter corresponds to the value that you want to filter to.

So, this would return only those players called "Sam Minnée".

$players = Player::get()->filter([
    'FirstName' => 'Sam',
    'LastName' => 'Minnée',
]);

// SELECT * FROM Player WHERE FirstName = 'Sam' AND LastName = 'Minnée'

There is also a shorthand way of getting Players with the FirstName of Sam.

$players = Player::get()->filter('FirstName', 'Sam');

Or if you want to find both Sam and Sig.

$players = Player::get()->filter('FirstName', ['Sam', 'Sig']);

// SELECT * FROM Player WHERE FirstName IN ('Sam', 'Sig')

You can use SearchFilters to add additional behavior to your filter command rather than an exact match.

$players = Player::get()->filter([
    'FirstName:StartsWith' => 'S',
    'PlayerNumber:GreaterThan' => '10',
]);

filterAny#

Use the filterAny() method to match multiple criteria non-exclusively (with an "OR" disjunctive),

$players = Player::get()->filterAny([
    'FirstName' => 'Sam',
    'Age' => 17,
]);

// SELECT * FROM Player WHERE ("FirstName" = 'Sam' OR "Age" = '17')

You can combine both conjunctive ("AND") and disjunctive ("OR") statements.

$players = Player::get()
    ->filter([
        'LastName' => 'Minnée',
    ])
    ->filterAny([
        'FirstName' => 'Sam',
        'Age' => 17,
    ]);
// SELECT * FROM Player WHERE ("LastName" = 'Minnée' AND ("FirstName" = 'Sam' OR "Age" = '17'))

You can use SearchFilters to add additional behavior to your filterAny command.

$players = Player::get()->filterAny([
    'FirstName:StartsWith' => 'S',
    'PlayerNumber:GreaterThan' => '10',
]);

Filtering by null values#

Since null values in SQL are special, they are non-comparable with other values, certain filters will add IS NULL or IS NOT NULL predicates automatically to your query. As per ANSI SQL-92, any comparison condition against a field will filter out nulls by default. Therefore, it's necessary to include certain null checks to ensure that exclusion filters behave predictably.

For instance, the below code will select only values that do not match the given value, including nulls.

$players = Player::get()->filter('FirstName:not', 'Sam');
// ... WHERE "FirstName" != 'Sam' OR "FirstName" IS NULL
// Returns rows with any value (even null) other than Sam

If null values should be excluded, include the null in your check.

$players = Player::get()->filter('FirstName:not', ['Sam', null]);
// ... WHERE "FirstName" != 'Sam' AND "FirstName" IS NOT NULL
// Only returns non-null values for "FirstName" that aren't Sam.
// Strictly the IS NOT NULL isn't necessary, but is included for explicitness

It is also often useful to filter by all rows with either empty or null for a given field.

$players = Player::get()->filter('FirstName', [null, '']);
// ... WHERE "FirstName" == '' OR "FirstName" IS NULL
// Returns rows with FirstName which is either empty or null

Filtering by aggregates#

You can use aggregate expressions in your filters, as well.

// get the teams that have more than 10 players
$teams = Team::get()->filter('Players.Count():GreaterThan', 10);

// get the teams with at least one player who has scored 5 or more points
$teams = Team::get()->filter('Players.Min(PointsScored):GreaterThanOrEqual', 5);

// get the teams with players who are averaging more than 15 points
$teams = Team::get()->filter('Players.Avg(PointsScored):GreaterThan', 15);

// get the teams whose players have scored less than 300 points combined
$teams = Team::get()->filter('Players.Sum(PointsScored):LessThan', 300);

filterByCallback#

It is also possible to filter by a PHP callback, this will force the data model to fetch all records and loop them in PHP, thus filter() or filterAny() are to be preferred over filterByCallback().

The first parameter to the callback is the item, the second parameter is the list itself. The callback will run once for each record, if the callback returns true, this record will be added to the list of returned items.

The below example will get all Players aged over 10.

$players = Player::get()->filterByCallback(function ($item, $list) {
    return ($item->Age() > 10);
});

exclude#

The exclude() method is the opposite to the filter in that it removes entries from a list.

$players = Player::get()->exclude('FirstName', 'Sam');

// SELECT * FROM Player WHERE FirstName != 'Sam'

Remove both Sam and Sig..

$players = Player::get()->exclude([
    'FirstName' => ['Sam','Sig'],
]);

Exclude follows the same pattern as filter, so for removing only Sam Minnée from the list:

$players = Player::get()->exclude([
    'FirstName' => 'Sam',
    'Surname' => 'Minnée',
]);

// SELECT * FROM Player WHERE (FirstName != 'Sam' OR LastName != 'Minnée')

Removing players with either the first name of Sam or the last name of Minnée requires multiple ->exclude calls:

$players = Player::get()->exclude('FirstName', 'Sam')->exclude('Surname', 'Minnée');

// SELECT * FROM Player WHERE FirstName != 'Sam' AND LastName != 'Minnée'

And removing Sig and Sam with that are either age 17 or 43.

$players = Player::get()->exclude([
    'FirstName' => ['Sam', 'Sig'],
    'Age' => [17, 43],
]);

// SELECT * FROM Player WHERE ("FirstName" NOT IN ('Sam','Sig) OR "Age" NOT IN ('17', '43'));

You can use SearchFilters to add additional behavior to your exclude command.

$players = Player::get()->exclude([
    'FirstName:EndsWith' => 'S',
    'PlayerNumber:LessThanOrEqual' => '10',
]);

subtract#

You can subtract entries from a DataList by passing in another DataList to subtract()

$sam = Player::get()->filter('FirstName', 'Sam');
$players = Player::get();

$noSams = $players->subtract($sam);

Though for the above example it would probably be easier to use filter() and exclude(). A better use case could be when you want to find all the members that does not exist in a Group.

// ... Finding all members that does not belong to $group.
use SilverStripe\Security\Member;
$otherMembers = Member::get()->subtract($group->Members());

limit#

You can limit the amount of records returned in a DataList by using the limit() method.

use SilverStripe\Security\Member;
$members = Member::get()->limit(5);

limit() accepts two arguments, the first being the amount of results you want returned, with an optional second parameter to specify the offset, which allows you to tell the system where to start getting the results from. The offset, if not provided as an argument, will default to 0.

// Return 10 members with an offset of 4 (starting from the 5th result).
$members = Member::get()->sort('Surname')->limit(10, 4);

Mapping classes to tables with DataObjectSchema#

Note that in most cases, the underlying database table for any DataObject instance will be the same as the class name. However in cases where dealing with namespaced classes, especially when using DB schema which don't support slashes in table names, it is necessary to provide an alternate mapping.

For instance, the below model will be stored in the table name BannerImage

namespace SilverStripe\BannerManager;

use SilverStripe\ORM\DataObject;

class BannerImage extends DataObject
{
    private static $table_name = 'BannerImage';
}

Note that any model class which does not explicitly declare a table_name config option will have a name automatically generated for them. In the above case, the table name would have been SilverStripe\BannerManager\BannerImage

When creating raw SQL queries that contain table names, it is necessary to ensure your queries have the correct table. This functionality can be provided by the DataObjectSchema service, which can be accessed via DataObject::getSchema(). This service provides the following methods, most of which have a table and class equivalent version.

Methods which return class names:

• tableClass($table) Finds the class name for a given table. This also handles suffixed tables such as Table_Live.
• baseDataClass($class) Returns the base data class for the given class.
• classForField($class, $field) Finds the specific class that directly holds the given field

Methods which return table names:

• tableName($class) Returns the table name for a given class or object.
• baseDataTable($class) Returns the base data class for the given class.
• tableForField($class, $field) Finds the specific class that directly holds the given field and returns the table.

Note that in cases where the class name is required, an instance of the object may be substituted.

For example, if running a query against a particular model, you will need to ensure you use the correct table and column.

use SilverStripe\ORM\DataObject;
use SilverStripe\ORM\Queries\SQLSelect;

public function countDuplicates($model, $fieldToCheck)
{
    $table = DataObject::getSchema()->tableForField($model, $field);
    $query = SQLSelect::create();
    $query->setFrom("\"{$table}\"");
    $query->setWhere(["\"{$table}\".\"{$field}\"" => $model->$fieldToCheck]);
    return $query->count();
}

Raw SQL#

Occasionally, the system described above won't let you do exactly what you need to do. In these situations, we have methods that manipulate the SQL query at a lower level. When using these, please ensure that all table and field names are escaped with double quotes, otherwise some DB backends (e.g. PostgreSQL) won't work.

Under the hood, query generation is handled by the DataQuery class. This class does provide more direct access to certain SQL features that DataList abstracts away from you.

In general, we advise against using these methods unless it's absolutely necessary. If the ORM doesn't do quite what you need it to, you may also consider extending the ORM with new data types or filter modifiers

Where clauses#

You can specify a WHERE clause fragment (that will be combined with other filters using AND) with the where() method:

$members = Member::get()->where("\"FirstName\" = 'Sam'");

Joining tables#

You can specify a join with the innerJoin and leftJoin methods. Both of these methods have the same arguments:

• The name of the table to join to.
• The filter clause for the join.
• An optional alias.

// Without an alias
$members = Member::get()
    ->leftJoin('Group_Members', '"Group_Members"."MemberID" = "Member"."ID"');

$members = Member::get()
    ->innerJoin('Group_Members', '"Rel"."MemberID" = "Member"."ID"', 'Rel');

Default values#

Define the default values for all the $db fields. This example sets the "Status"-column on Player to "Active" whenever a new object is created.

namespace App\Model;

use SilverStripe\ORM\DataObject;

class Player extends DataObject
{
    private static $defaults = [
        'Status' => 'Active',
    ];
}

Subclasses#

Inheritance is supported in the data model: separate tables will be linked together, the data spread across these tables. The mapping and saving logic is handled by Silverstripe CMS , you don't need to worry about writing SQL most of the time.

For example, suppose we have the following set of classes:

namespace {

    use SilverStripe\CMS\Model\SiteTree;

    class Page extends SiteTree
    {
        // ...
    }
}

namespace App\PageType;

use Page;

class NewsPage extends Page
{
    private static $db = [
        'Summary' => 'Text',
    ];
}

The data for the following classes would be stored across the following tables:

SilverStripe\CMS\Model\SiteTree:
  ID: Int
  ClassName: Enum('SiteTree', 'Page', 'NewsPage')
  Created: Datetime
  LastEdited: Datetime
  Title: Varchar
  Content: Text

App\PageType\NewsPage:
  ID: Int
  Summary: Text

Accessing the data is transparent to the developer.

$news = NewsPage::get();

foreach ($news as $article) {
    echo $article->Title;
}

The way the ORM stores the data is this:

• "Base classes" are direct sub-classes of DataObject. They are always given a table, whether or not they have special fields. This is called the "base table". In our case, SiteTree is the base table.
• The base table's ClassName field is set to class of the given record. It's an enumeration of all possible sub-classes of the base class (including the base class itself).
• Each sub-class of the base object will also be given its own table, as long as it has custom fields. In the example above, NewsSection didn't have its own data, so an extra table would be redundant.
• In all the tables, ID is the primary key. A matching ID number is used for all parts of a particular record: record #2 in Page refers to the same object as record #2 in SiteTree.

To retrieve a news article, Silverstripe CMS joins the SiteTree, Page and NewsPage tables by their ID fields.

Related lessons#

• Introduction to the ORM
• Adding custom fields to a page

Related documentation#

• Data Types and Casting

API documentation#

• DataObject
• DataList
• DataQuery
• DataObjectSchema