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589 lines
18 KiB
Markdown
589 lines
18 KiB
Markdown
title: Introduction to the Data Model and ORM
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summary: Introduction to creating and querying a database records through the ORM (object-relational model)
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# Introduction to the Data Model and ORM
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SilverStripe uses an [object-relational model](http://en.wikipedia.org/wiki/Object-relational_model) to represent its
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information.
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* Each database table maps to a PHP class.
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* Each database row maps to a PHP object.
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* Each database column maps to a property on a PHP object.
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All data tables in SilverStripe are defined as subclasses of [api:DataObject]. The [api:DataObject] class represents a
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single row in a database table, following the ["Active Record"](http://en.wikipedia.org/wiki/Active_record_pattern)
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design pattern. Database Columns are is defined as [Data Types](data_types_and_casting) in the static `$db` variable
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along with any [relationships](../relations) defined as `$has_one`, `$has_many`, `$many_many` properties on the class.
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Let's look at a simple example:
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**mysite/code/Player.php**
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:::php
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<?php
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class Player extends DataObject {
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private static $db = array(
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'PlayerNumber' => 'Int',
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'FirstName' => 'Varchar(255)',
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'LastName' => 'Text',
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'Birthday' => 'Date'
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);
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}
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This `Player` class definition will create a database table `Player` with columns for `PlayerNumber`, `FirstName` and
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so on. After writing this class, we need to regenerate the database schema.
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## Generating the Database Schema
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After adding, modifying or removing `DataObject` subclasses, make sure to rebuild your SilverStripe database. The
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database schema is generated automatically by visiting the URL http://www.yoursite.com/dev/build while authenticated as an administrator.
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This script will analyze the existing schema, compare it to what's required by your data classes, and alter the schema
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as required.
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It will perform the following changes:
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* Create any missing tables
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* Create any missing fields
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* Create any missing indexes
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* Alter the field type of any existing fields
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* Rename any obsolete tables that it previously created to _obsolete_(tablename)
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It **won't** do any of the following
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* Delete tables
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* Delete fields
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* Rename any tables that it doesn't recognize. This allows other applications to coexist in the same database, as long as
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their table names don't match a SilverStripe data class.
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<div class="notice" markdown='1'>
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You need to be logged in as an administrator to perform this command, unless your site is in [dev mode](../debugging),
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or the command is run through [CLI](../cli).
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</div>
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When rebuilding the database schema through the [api:SS_ClassLoader] the following additional properties are
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automatically set on the `DataObject`.
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* ID: Primary Key. When a new record is created, SilverStripe does not use the database's built-in auto-numbering
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system. Instead, it will generate a new `ID` by adding 1 to the current maximum ID.
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* ClassName: An enumeration listing this data-class and all of its subclasses.
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* Created: A date/time field set to the creation date of this record
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* LastEdited: A date/time field set to the date this record was last edited through `write()`
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**mysite/code/Player.php**
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:::php
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<?php
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class Player extends DataObject {
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private static $db = array(
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'PlayerNumber' => 'Int',
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'FirstName' => 'Varchar(255)',
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'LastName' => 'Text',
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'Birthday' => 'Date'
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);
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}
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Generates the following `SQL`.
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CREATE TABLE `Player` (
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`ID` int(11) NOT NULL AUTO_INCREMENT,
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`ClassName` enum('Player') DEFAULT 'Player',
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`LastEdited` datetime DEFAULT NULL,
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`Created` datetime DEFAULT NULL,
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`PlayerNumber` int(11) NOT NULL DEFAULT '0',
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`FirstName` varchar(255) DEFAULT NULL,
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`LastName` mediumtext,
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`Birthday` datetime DEFAULT NULL,
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PRIMARY KEY (`ID`),
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KEY `ClassName` (`ClassName`)
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);
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## Creating Data Records
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A new instance of a [api:DataObject] can be created using the `new` syntax.
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:::php
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$player = new Player();
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Or, a better way is to use the `create` method.
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:::php
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$player = Player::create();
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<div class="notice" markdown='1'>
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Using the `create()` method provides chainability, which can create add elegance and brevity to your code, e.g. `Player::create()->write()`. More importantly, however, it will look up the class in the [Injector](../extending/injector) so that can the class can be overriden by [dependency injection](http://en.wikipedia.org/wiki/Dependency_injection).
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</div>
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Database columns and properties can be set as class properties on the object. The SilverStripe ORM handles the saving
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of the values through a custom `__set()` method.
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:::php
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$player->FirstName = "Sam";
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$player->PlayerNumber = 07;
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To save the `DataObject` to the database, use the `write()` method. The first time `write()` is called, an `ID` will be
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set.
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:::php
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$player->write();
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For convenience, the `write()` method returns the record's ID. This is particularly useful when creating new records.
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:::php
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$player = Player::create();
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$id = $player->write();
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## Querying Data
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With the `Player` class defined we can query our data using the `ORM` or Object-Relational Model. The `ORM` provides
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shortcuts and methods for fetching, sorting and filtering data from our database.
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:::php
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$players = Player::get();
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// returns a `DataList` containing all the `Player` objects.
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$player = Player::get()->byId(2);
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// returns a single `Player` object instance that has the ID of 2.
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echo $player->ID;
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// returns the players 'ID' column value
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echo $player->dbObject('LastEdited')->Ago();
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// calls the `Ago` method on the `LastEdited` property.
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The `ORM` uses a "fluent" syntax, where you specify a query by chaining together different methods. Two common methods
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are `filter()` and `sort()`:
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:::php
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$members = Player::get()->filter(array(
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'FirstName' => 'Sam'
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))->sort('Surname');
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// returns a `DataList` containing all the `Player` records that have the `FirstName` of 'Sam'
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<div class="info" markdown="1">
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Provided `filter` values are automatically escaped and do not require any escaping.
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</div>
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## Lazy Loading
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The `ORM` doesn't actually execute the [api:SQLQuery] until you iterate on the result with a `foreach()` or `<% loop %>`.
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It's smart enough to generate a single efficient query at the last moment in time without needing to post-process the
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result set in PHP. In `MySQL` the query generated by the ORM may look something like this
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:::php
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$players = Player::get()->filter(array(
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'FirstName' => 'Sam'
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));
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$players = $players->sort('Surname');
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// executes the following single query
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// SELECT * FROM Player WHERE FirstName = 'Sam' ORDER BY Surname
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This also means that getting the count of a list of objects will be done with a single, efficient query.
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:::php
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$players = Player::get()->filter(array(
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'FirstName' => 'Sam'
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))->sort('Surname');
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// This will create an single SELECT COUNT query
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// SELECT COUNT(*) FROM Player WHERE FirstName = 'Sam'
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echo $players->Count();
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## Looping over a list of objects
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`get()` returns a `DataList` instance. You can loop over `DataList` instances in both PHP and templates.
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:::php
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$players = Player::get();
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foreach($players as $player) {
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echo $player->FirstName;
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}
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Notice that we can step into the loop safely without having to check if `$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.
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:::php
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$players = Player::get();
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if($players->exists()) {
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// do something here
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}
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See the [Lists](../lists) documentation for more information on dealing with [api:SS_List] instances.
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## Returning a single DataObject
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There are a couple of ways of getting a single DataObject from the ORM. If you know the ID number of the object, you
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can use `byID($id)`:
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:::php
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$player = Player::get()->byID(5);
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`get()` returns a [api:DataList] instance. You can use operations on that to get back a single record.
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:::php
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$players = Player::get();
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$first = $players->first();
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$last = $players->last();
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## Sorting
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If would like to sort the list by `FirstName` in a ascending way (from A to Z).
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:::php
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// Sort can either be Ascending (ASC) or Descending (DESC)
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$players = Player::get()->sort('FirstName', 'ASC');
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// Ascending is implied
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$players = Player::get()->sort('FirstName');
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To reverse the sort
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:::php
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$players = Player::get()->sort('FirstName', 'DESC');
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// or..
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$players = Player::get()->sort('FirstName', 'ASC')->reverse();
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However you might have several entries with the same `FirstName` and would like to sort them by `FirstName` and
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`LastName`
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:::php
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$players = Players::get()->sort(array(
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'FirstName' => 'ASC',
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'LastName'=>'ASC'
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));
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You can also sort randomly.
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:::php
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$players = Player::get()->sort('RAND()')
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## Filtering Results
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The `filter()` method filters the list of objects that gets returned.
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:::php
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$players = Player::get()->filter(array(
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'FirstName' => 'Sam'
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));
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Each element of the array specifies a filter. You can specify as many filters as you like, and they **all** must be
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true for the record to be included in the result.
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The key in the filter corresponds to the field that you want to filter and the value in the filter corresponds to the
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value that you want to filter to.
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So, this would return only those players called "Sam Minnée".
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:::php
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$players = Player::get()->filter(array(
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'FirstName' => 'Sam',
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'LastName' => 'Minnée',
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));
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// SELECT * FROM Player WHERE FirstName = 'Sam' AND LastName = 'Minnée'
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There is also a shorthand way of getting Players with the FirstName of Sam.
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:::php
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$players = Player::get()->filter('FirstName', 'Sam');
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Or if you want to find both Sam and Sig.
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:::php
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$players = Player::get()->filter(
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'FirstName', array('Sam', 'Sig')
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);
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// SELECT * FROM Player WHERE FirstName IN ('Sam', 'Sig')
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You can use [SearchFilters](searchfilters) to add additional behavior to your `filter` command rather than an
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exact match.
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:::php
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$players = Player::get()->filter(array(
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'FirstName:StartsWith' => 'S'
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'PlayerNumber:GreaterThan' => '10'
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));
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### filterAny
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Use the `filterAny()` method to match multiple criteria non-exclusively (with an "OR" disjunctive),
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:::php
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$players = Player::get()->filterAny(array(
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'FirstName' => 'Sam',
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'Age' => 17,
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));
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// SELECT * FROM Player WHERE ("FirstName" = 'Sam' OR "Age" = '17')
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You can combine both conjunctive ("AND") and disjunctive ("OR") statements.
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:::php
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$players = Player::get()
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->filter(array(
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'LastName' => 'Minnée'
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))
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->filterAny(array(
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'FirstName' => 'Sam',
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'Age' => 17,
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));
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// SELECT * FROM Player WHERE ("LastName" = 'Minnée' AND ("FirstName" = 'Sam' OR "Age" = '17'))
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You can use [SearchFilters](searchfilters) to add additional behavior to your `filterAny` command.
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:::php
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$players = Player::get()->filterAny(array(
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'FirstName:StartsWith' => 'S'
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'PlayerNumber:GreaterThan' => '10'
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));
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### filterByCallback
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It is also possible to filter by a PHP callback, this will force the data model to fetch all records and loop them in
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PHP, thus `filter()` or `filterAny()` are to be preferred over `filterByCallback()`.
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<div class="notice" markdown="1">
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Because `filterByCallback()` has to run in PHP, it has a significant performance tradeoff, and should not be used on large recordsets.
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`filterByCallback()` will always return an `ArrayList`.
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</div>
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The first parameter to the callback is the item, the second parameter is the list itself. The callback will run once
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for each record, if the callback returns true, this record will be added to the list of returned items.
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The below example will get all `Players` aged over 10.
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:::php
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$players = Player::get()->filterByCallback(function($item, $list) {
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return ($item->Age() > 10);
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});
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### Exclude
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The `exclude()` method is the opposite to the filter in that it removes entries from a list.
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:::php
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$players = Player::get()->exclude('FirstName', 'Sam');
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// SELECT * FROM Player WHERE FirstName != 'Sam'
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Remove both Sam and Sig..
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:::php
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$players = Player::get()->exclude(
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'FirstName', array('Sam','Sig')
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);
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`Exclude` follows the same pattern as filter, so for removing only Sam Minnée from the list:
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:::php
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$players = Player::get()->exclude(array(
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'FirstName' => 'Sam',
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'Surname' => 'Minnée',
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));
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And removing Sig and Sam with that are either age 17 or 74.
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:::php
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$players = Player::get()->exclude(array(
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'FirstName' => array('Sam', 'Sig'),
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'Age' => array(17, 43)
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));
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// SELECT * FROM Player WHERE ("FirstName" NOT IN ('Sam','Sig) OR "Age" NOT IN ('17', '74));
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You can use [SearchFilters](searchfilters) to add additional behavior to your `exclude` command.
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:::php
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$players = Player::get()->exclude(array(
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'FirstName:EndsWith' => 'S'
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'PlayerNumber:LessThanOrEqual' => '10'
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));
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### Subtract
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You can subtract entries from a [api:DataList] by passing in another DataList to `subtract()`
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:::php
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$sam = Player::get()->filter('FirstName', 'Sam');
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$players = Player::get();
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$noSams = $players->subtract($sam);
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Though for the above example it would probably be easier to use `filter()` and `exclude()`. A better use case could be
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when you want to find all the members that does not exist in a Group.
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:::php
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// ... Finding all members that does not belong to $group.
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$otherMembers = Member::get()->subtract($group->Members());
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### Limit
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You can limit the amount of records returned in a DataList by using the `limit()` method.
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:::php
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$members = Member::get()->limit(5);
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`limit()` accepts two arguments, the first being the amount of results you want returned, with an optional second
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parameter to specify the offset, which allows you to tell the system where to start getting the results from. The
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offset, if not provided as an argument, will default to 0.
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:::php
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// Return 10 members with an offset of 4 (starting from the 5th result).
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$members = Member::get()->sort('Surname')->limit(10, 4);
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<div class="alert">
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Note that the `limit` argument order is different from a MySQL LIMIT clause.
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</div>
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### Raw SQL
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Occasionally, the system described above won't let you do exactly what you need to do. In these situations, we have
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methods that manipulate the SQL query at a lower level. When using these, please ensure that all table and field names
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are escaped with double quotes, otherwise some DB backends (e.g. PostgreSQL) won't work.
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Under the hood, query generation is handled by the `[api:DataQuery]` class. This class does provide more direct access
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to certain SQL features that `DataList` abstracts away from you.
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In general, we advise against using these methods unless it's absolutely necessary. If the ORM doesn't do quite what
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you need it to, you may also consider extending the ORM with new data types or filter modifiers
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#### Where clauses
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You can specify a WHERE clause fragment (that will be combined with other filters using AND) with the `where()` method:
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:::php
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$members = Member::get()->where("\"FirstName\" = 'Sam'")
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#### Joining Tables
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You can specify a join with the `innerJoin` and `leftJoin` methods. Both of these methods have the same arguments:
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* The name of the table to join to.
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* The filter clause for the join.
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* An optional alias.
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:::php
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// Without an alias
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$members = Member::get()
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->leftJoin("Group_Members", "\"Group_Members\".\"MemberID\" = \"Member\".\"ID\"");
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$members = Member::get()
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->innerJoin("Group_Members", "\"Rel\".\"MemberID\" = \"Member\".\"ID\"", "Rel");
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<div class="alert" markdown="1">
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Passing a *$join* statement to will filter results further by the JOINs performed against the foreign table. It will
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**not** return the additionally joined data.
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</div>
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### Default Values
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Define the default values for all the `$db` fields. This example sets the "Status"-column on Player to "Active"
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whenever a new object is created.
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:::php
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<?php
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class Player extends DataObject {
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private static $defaults = array(
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"Status" => 'Active',
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);
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}
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<div class="notice" markdown='1'>
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Note: Alternatively you can set defaults directly in the database-schema (rather than the object-model). See
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[Data Types and Casting](data-types) for details.
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</div>
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## Subclasses
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Inheritance is supported in the data model: separate tables will be linked together, the data spread across these
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tables. The mapping and saving logic is handled by SilverStripe, you don't need to worry about writing SQL most of the
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time.
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For example, suppose we have the following set of classes:
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:::php
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<?php
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class Page extends SiteTree {
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}
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class NewsPage extends Page {
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private static $db = array(
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'Summary' => 'Text'
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);
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}
|
|
|
|
The data for the following classes would be stored across the following tables:
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|
|
|
:::yml
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|
SiteTree:
|
|
- ID: Int
|
|
- ClassName: Enum('SiteTree', 'Page', 'NewsPage')
|
|
- Created: Datetime
|
|
- LastEdited: Datetime
|
|
- Title: Varchar
|
|
- Content: Text
|
|
NewsArticle:
|
|
- ID: Int
|
|
- Summary: Text
|
|
|
|
Accessing the data is transparent to the developer.
|
|
|
|
:::php
|
|
$news = NewsPage::get();
|
|
|
|
foreach($news as $article) {
|
|
echo $news->Title;
|
|
}
|
|
|
|
The way the ORM stores the data is this:
|
|
|
|
* "Base classes" are direct sub-classes of [api: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 `[api:SiteTree]`.
|
|
|
|
To retrieve a news article, SilverStripe joins the [api:SiteTree], [api:Page] and NewsArticle tables by their ID fields.
|
|
|
|
## Related Documentation
|
|
|
|
* [Data Types and Casting](../data_types_and_casting)
|
|
|
|
## API Documentation
|
|
|
|
* [api:DataObject]
|
|
* [api:DataList]
|
|
* [api:DataQuery]
|