mirror of
https://github.com/silverstripe/silverstripe-framework
synced 2024-09-18 23:46:21 +02:00
299 lines
8.1 KiB
Markdown
299 lines
8.1 KiB
Markdown
title: Relations between Records
|
|
summary: Relate models together using the ORM using has_one, has_many, and many_many.
|
|
|
|
# Relations between Records
|
|
|
|
In most situations you will likely see more than one [api:DataObject] and several classes in your data model may relate
|
|
to one another. An example of this is a `Player` object may have a relationship to one or more `Team` or `Coach` classes
|
|
and could take part in many `Games`. Relations are a key part of designing and building a good data model.
|
|
|
|
Relations are built through static array definitions on a class, in the format `<relationship-name> => <classname>`.
|
|
SilverStripe supports a number of relationship types and each relationship type can have any number of relations.
|
|
|
|
## has_one
|
|
|
|
A 1-to-1 relation creates a database-column called "`<relationship-name>`ID", in the example below this would be
|
|
"TeamID" on the "Player"-table.
|
|
|
|
:::php
|
|
<?php
|
|
|
|
class Team extends DataObject {
|
|
|
|
private static $db = array(
|
|
'Title' => 'Varchar'
|
|
);
|
|
|
|
private static $has_many = array(
|
|
'Players' => 'Player'
|
|
);
|
|
}
|
|
|
|
class Player extends DataObject {
|
|
|
|
private static $has_one = array(
|
|
"Team" => "Team",
|
|
);
|
|
}
|
|
|
|
This defines a relationship called `Team` which links to a `Team` class. The `ORM` handles navigating the relationship
|
|
and provides a short syntax for accessing the related object.
|
|
|
|
At the database level, the `has_one` creates a `TeamID` field on `Player`. A `has_many` field does not impose any database changes. It merely injects a new method into the class to access the related records (in this case, `Players()`)
|
|
|
|
:::php
|
|
$player = Player::get()->byId(1);
|
|
|
|
$team = $player->Team();
|
|
// returns a 'Team' instance.
|
|
|
|
echo $player->Team()->Title;
|
|
// returns the 'Title' column on the 'Team' or `getTitle` if it exists.
|
|
|
|
The relationship can also be navigated in [templates](../templates).
|
|
|
|
:::ss
|
|
<% with $Player %>
|
|
<% if $Team %>
|
|
Plays for $Team.Title
|
|
<% end_if %>
|
|
<% end_with %>
|
|
|
|
## has_many
|
|
|
|
Defines 1-to-many joins. As you can see from the previous example, `$has_many` goes hand in hand with `$has_one`.
|
|
|
|
<div class="alert" markdown='1'>
|
|
Please specify a $has_one-relationship on the related child-class as well, in order to have the necessary accessors
|
|
available on both ends.
|
|
</div>
|
|
|
|
:::php
|
|
<?php
|
|
|
|
class Team extends DataObject {
|
|
|
|
private static $db = array(
|
|
'Title' => 'Varchar'
|
|
);
|
|
|
|
private static $has_many = array(
|
|
'Players' => 'Player'
|
|
);
|
|
}
|
|
|
|
class Player extends DataObject {
|
|
|
|
private static $has_one = array(
|
|
"Team" => "Team",
|
|
);
|
|
}
|
|
|
|
Much like the `has_one` relationship, `has_many` can be navigated through the `ORM` as well. The only difference being
|
|
you will get an instance of [api:HasManyList] rather than the object.
|
|
|
|
:::php
|
|
$team = Team::get()->first();
|
|
|
|
echo $team->Players();
|
|
// [HasManyList]
|
|
|
|
echo $team->Players()->Count();
|
|
// returns '14';
|
|
|
|
foreach($team->Players() as $player) {
|
|
echo $player->FirstName;
|
|
}
|
|
|
|
To specify multiple $has_manys to the same object you can use dot notation to distinguish them like below:
|
|
|
|
:::php
|
|
<?php
|
|
|
|
class Person extends DataObject {
|
|
|
|
private static $has_many = array(
|
|
"Managing" => "Company.Manager",
|
|
"Cleaning" => "Company.Cleaner",
|
|
);
|
|
}
|
|
|
|
class Company extends DataObject {
|
|
|
|
private static $has_one = array(
|
|
"Manager" => "Person",
|
|
"Cleaner" => "Person"
|
|
);
|
|
}
|
|
|
|
|
|
Multiple `$has_one` relationships are okay if they aren't linking to the same object type. Otherwise, they have to be
|
|
named.
|
|
|
|
|
|
## belongs_to
|
|
|
|
Defines a 1-to-1 relationship with another object, which declares the other end of the relationship with a
|
|
corresponding $has_one. A single database column named `<relationship-name>ID` will be created in the object with the
|
|
`$has_one`, but the $belongs_to by itself will not create a database field. This field will hold the ID of the object
|
|
declaring the `$belongs_to`.
|
|
|
|
Similarly with $has_many, dot notation can be used to explicitly specify the `$has_one` which refers to this relation.
|
|
This is not mandatory unless the relationship would be otherwise ambiguous.
|
|
|
|
:::php
|
|
<?php
|
|
|
|
class Team extends DataObject {
|
|
|
|
private static $has_one = array(
|
|
'Coach' => 'Coach'
|
|
);
|
|
}
|
|
|
|
class Coach extends DataObject {
|
|
|
|
private static $belongs_to = array(
|
|
'Team' => 'Team.Coach'
|
|
);
|
|
}
|
|
|
|
|
|
## many_many
|
|
|
|
Defines many-to-many joins. A new table, (this-class)_(relationship-name), will be created with a pair of ID fields.
|
|
|
|
<div class="warning" markdown='1'>
|
|
Please specify a $belongs_many_many-relationship on the related class as well, in order to have the necessary accessors
|
|
available on both ends.
|
|
</div>
|
|
|
|
:::php
|
|
<?php
|
|
|
|
class Team extends DataObject {
|
|
|
|
private static $many_many = array(
|
|
"Supporters" => "Supporter",
|
|
);
|
|
}
|
|
|
|
class Supporter extends DataObject {
|
|
|
|
private static $belongs_many_many = array(
|
|
"Supports" => "Team",
|
|
);
|
|
}
|
|
|
|
Much like the `has_one` relationship, `many_many` can be navigated through the `ORM` as well. The only difference being
|
|
you will get an instance of [api:ManyManyList] rather than the object.
|
|
|
|
:::php
|
|
$team = Team::get()->byId(1);
|
|
|
|
$supporters = $team->Supporters();
|
|
// returns a 'ManyManyList' instance.
|
|
|
|
|
|
The relationship can also be navigated in [templates](../templates).
|
|
|
|
:::ss
|
|
<% with $Supporter %>
|
|
<% loop $Supports %>
|
|
Supports $Title
|
|
<% end_if %>
|
|
<% end_with %>
|
|
|
|
To specify multiple $many_manys between the same classes, use the dot notation to distinguish them like below:
|
|
|
|
:::php
|
|
<?php
|
|
|
|
class Category extends DataObject {
|
|
|
|
private static $many_many = array(
|
|
'Products' => 'Product',
|
|
'FeaturedProducts' => 'Product'
|
|
);
|
|
}
|
|
|
|
class Product extends DataObject {
|
|
|
|
private static $belongs_many_many = array(
|
|
'Categories' => 'Category.Products',
|
|
'FeaturedInCategories' => 'Category.FeaturedProducts'
|
|
);
|
|
}
|
|
|
|
## many_many or belongs_many_many?
|
|
|
|
If you're unsure about whether an object should take on `many_many` or `belongs_many_many`, the best way to think about it is that the object where the relationship will be edited (i.e. via checkboxes) should contain the `many_many`. For instance, in a `many_many` of Product => Categories, the `Product` should contain the `many_many`, because it is much more likely that the user will select Categories for a Product than vice-versa.
|
|
|
|
|
|
## Adding relations
|
|
|
|
Adding new items to a relations works the same, regardless if you're editing a **has_many** or a **many_many**. They are
|
|
encapsulated by [api:HasManyList] and [api:ManyManyList], both of which provide very similar APIs, e.g. an `add()`
|
|
and `remove()` method.
|
|
|
|
:::php
|
|
$team = Team::get()->byId(1);
|
|
|
|
// create a new supporter
|
|
$supporter = new Supporter();
|
|
$supporter->Name = "Foo";
|
|
$supporter->write();
|
|
|
|
// add the supporter.
|
|
$team->Supporters()->add($supporter);
|
|
|
|
|
|
## Custom Relations
|
|
|
|
You can use the ORM to get a filtered result list without writing any SQL. For example, this snippet gets you the
|
|
"Players"-relation on a team, but only containing active players.
|
|
|
|
See `[api:DataObject::$has_many]` for more info on the described relations.
|
|
|
|
:::php
|
|
<?php
|
|
|
|
class Team extends DataObject {
|
|
|
|
private static $has_many = array(
|
|
"Players" => "Player"
|
|
);
|
|
|
|
public function ActivePlayers() {
|
|
return $this->Players()->filter('Status', 'Active');
|
|
}
|
|
}
|
|
|
|
<div class="notice" markdown="1">
|
|
Adding new records to a filtered `RelationList` like in the example above doesn't automatically set the filtered
|
|
criteria on the added record.
|
|
</div>
|
|
|
|
## Relations on Unsaved Objects
|
|
|
|
You can also set *has_many* and *many_many* relations before the `DataObject` is saved. This behavior uses the
|
|
[api:UnsavedRelationList] and converts it into the correct `RelationList` when saving the `DataObject` for the first
|
|
time.
|
|
|
|
This unsaved lists will also recursively save any unsaved objects that they contain.
|
|
|
|
As these lists are not backed by the database, most of the filtering methods on `DataList` cannot be used on a list of
|
|
this type. As such, an `UnsavedRelationList` should only be used for setting a relation before saving an object, not
|
|
for displaying the objects contained in the relation.
|
|
|
|
## Related Documentation
|
|
|
|
* [Introduction to the Data Model and ORM](data_model_and_orm)
|
|
* [Lists](lists)
|
|
|
|
## API Documentation
|
|
|
|
* [api:HasManyList]
|
|
* [api:ManyManyList]
|
|
* [api:DataObject]
|