# Handling Relations

1. [References](#references)
1. [Multiple References](#multiple-references)
1. [Self reference](#self-reference)
1. [Passing references to providers](#passing-references-to-providers)


## References

Let's get back to the Group. Ideally a group should have members, and Alice
allows you to reference one object from another one. You can do that with the
`@name` notation, where name is a fixture name from any class.

Let's add a fixed owner to the group:

```yaml
Nelmio\Entity\User:
    # ...

Nelmio\Entity\Group:
    group1:
        name: Admins
        owner: '@user1'
```

**Warning:** References (e.g. here `group1`) should always be composed of
letters, digits, periods (`.`), underscores (`_`) and slashes (`/`). Other
characters such as `{`, `}`, `(`, `)` are still allowed but hold a special
meaning (e.g. for [ranged fixtures](complete-reference.md#fixture-ranges)).

Alice also allows you to directly reference objects' properties using
the `@name->property` notation or calling an object method
`@name->getProperty()`.

```yaml
Nelmio\Entity\User:
    # ...

Nelmio\Entity\Group:
    group1:
        name: Admins
        owner: '@user1->username'
```

To be able to use this feature, your entities have to match some requirements :
* You can reference public properties
* You can reference properties reachable through a getter (i.e :
`@name->property` will call `$name->getProperty()` if ```property``` is not
public)
* You can reference private properties [by decorating the property accessor with the `ReflectionPropertyAccessor`](advanced-guide.md#custom-accessor)
* You can reference entities' ID but you will then have to split fixtures in
multiple files (this is because objects are persisted at the end of each file
processing) :

```yaml
# fixture_user.yml
Nelmio\Entity\User:
    # ...
```

```yaml
# fixture_group.yml
Nelmio\Entity\Group:
    group1:
        name: Admins
        owner: '@user1->id'
```

If you want to create ten users and ten groups and have each user own one
group, you can use `<current()>` which is replaced with the current ID of
each iteration when using fixture ranges:

```yaml
Nelmio\Entity\User:
    # ...

Nelmio\Entity\Group:
    group{1..10}:
        owner: '@user<current()>'
```

If you would like a random user instead of a fixed one, you can define a
reference with a wildcard:

```yaml
Nelmio\Entity\User:
    # ...

Nelmio\Entity\Group:
    group1:
        name: Admins
        owner: '@user*'
```

It will then pick any object whose name matches `user*` where `*` can be any
string.

It is also possible to create a relation to a random object by id:

```yaml
Nelmio\Entity\Group:
    group1:
        owner: '@user<numberBetween(1, 200)>'
```

> **Note**: To create a string `@foo` that is not a reference you can escape it
> as `\@foo`

> **Note**: When `@` is used in the middle of a word, e.g. `email@example.com`,
it will be automatically escaped.


## Multiple References

If we also want to add group members, there are two ways to do this.
One is to define an array of references to have a fixed set of members:

```yaml
Nelmio\Entity\User:
    # ...

Nelmio\Entity\Group:
    group1:
        name: Admins
        owner: '@user1'
        members: ['@user2', '@user3']
```

Another, which is more interesting, is to define a reference with a wildcard,
and also tell Alice how many object you want:

```yaml
Nelmio\Entity\User:
    # ...

Nelmio\Entity\Group:
    group1:
        name: Admins
        owner: '@user1'
        members: '5x @user*'
```

In this case it will pick 5 fixture objects which have a name matching `user*`.

You can also randomize the amount by combining it with faker data:

```yaml
    # ...
        members: '<numberBetween(1, 10)>x @user*'
```

If the data needs to be static instead, you can use the same syntax as
the one used for fixtures range.

```yaml
Nelmio\Entity\User:
    # ...

Nelmio\Entity\Group:
    group{1..10}:
        members: '@user{1..10}'
```

> **Note**: You do not need to define multi-references inside an array, since
> they are automatically translated to an array of objects.


## Self reference

The `@self` reference is assigned to the current fixture instance.

## Passing references to providers

You can pass references to providers much like you can pass [variables](fixtures-refactoring.md#variables):

```yaml
Nelmio\Entity\Group:
    group1:
        owner: '<numberBetween(1, 200)>'

    group2:
        owner: '<numberBetween(@group1->owner, 200)>'
```


<br />
<hr />

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