> For the complete documentation index, see [llms.txt](https://docs.objectiphy.net/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.objectiphy.net/defining-relationships/many-to-one.md).

# Many to one

Join a member of a collection or array of child entities to a parent entity.

This is the opposite of a one-to-many relationship, so is basically a one-to-many relationship as seen from the point of view of the child object. The entity holding the many-to-one relationship points to a single other entity (its parent), but it will be held in an array or collection along with siblings of the same type as itself.

As the entity holding the many-to-one relationship only points to a single parent object, as far as Objectiphy is concerned, it is treated almost identically to a [one-to-one relationship](/defining-relationships/one-to-one.md), and is defined in the same way - only the relationship type is different. The only difference in behaviour between many-to-one and one-to-one is when deleting data - ie. if orphan removal is enabled, it will check to make sure the object with a many-to-one relationship is not owned by any other parents before deleting it. Also, cascade deletes is not allowed on many-to-one relationships, as by definition, the child could belong to more than one parent. See the page on [deleting](/deleting.md) for more information about that.

For example, suppose we have a `Customer` entity and an `Order` entity, and a customer can have multiple orders. The `Order` entity has a many-to-one relationship with `Customer`. The code for these entities looks like this:

```php
class Customer
{
    public int $id;
    public string $name;
    public array $orders = []; // <--One to Many
}

// Note: Each class would of course normally be
// in a separate file.

class Order
{
    public int $id;
    public Customer $customer; // <--Many to one
    //... more properties
}

```

We store the values of the properties for these entities in two database tables, named `customer` and `order:`

| customer |
| -------- |
| `id`     |
| `name`   |

| order                                                            |
| ---------------------------------------------------------------- |
| `id`                                                             |
| `customer_id`  <mark style="color:green;"><-- Foreign key</mark> |
| `...more columns`                                                |

The `order` table contains a foreign key column named `customer_id` which holds the primary key value of the `customer` table. We have no choice over which side owns the relationship - only the `order` table can have a the foreign key, because a customer can have multiple orders, and we can't store multiple foreign keys in a single column.

### Examples

Here are two examples of how to set up the mapping for a many-to-one relationship using attributes or annotations (these examples are all equivalent; you only need to use one type of [mapping provider](/annotations.md), it is up to you which one).

As with [one-to-one](/defining-relationships/one-to-one.md#examples), note that the `sourceJoinColumn` attribute (or `@ORM\JoinColumn` annotation if using Doctrine annotations) exists on the owning side (`Order`), and the other side (`Customer`) has a `mappedBy` attribute, telling Objectiphy where to look for the join column. The value of `mappedBy` must be a *property* name, not a column name!

#### Example 1: Minimal Mapping

The following example shows the bare minimum mapping information necessary, on the assumption that the foreign key in the owning table is the primary key of the owned table and that a left join is sufficient. If you are using non-standard columns, or require an inner join, you will need to define them in full as shown in example 2 (note, if using Doctrine annotations, you cannot specify the join type with an annotation).

{% tabs %}
{% tab title="PHP8+ Attributes" %}

```php
use Objectiphy\Objectiphy\Table;
use Objectiphy\Objectiphy\Column;
use Objectiphy\Objectiphy\Relationship;

#[Table(name: 'customer')]
class Customer
{
    #[Column(isPrimaryKey: true)]
    public int $id;
    
    #[Column]
    public string $name;
    
    #[Relationship(
        relationshipType: 'one_to_many',
        childClassName: Order::class,
        mappedBy: 'customer'
    )]
    public array $orders = [];
}

// Note: Each class would of course normally be
// in a separate file.

#[Table(name: 'order')]
class Order
{
    #[Column(isPrimaryKey: true)]
    public int $id;
    
    #[Relationship(
        relationshipType: 'many_to_one',
        childClassName: Customer::class
    )]
    public Customer $customer;
    
    //... more properties
}

```

{% endtab %}

{% tab title="Objectiphy Annotations" %}

```php
use Objectiphy\Objectiphy\Table;
use Objectiphy\Objectiphy\Column;
use Objectiphy\Objectiphy\Relationship;

/**
 * @Table(name="customer")
 */
class Customer
{
    /**
     * @Column(isPrimaryKey=true)
     */ 
    public int $id;
    
    /**
     * @Column
     */
    public string $name;
    
    /**
     * @Relationship(
     *     relationshipType="one_to_many"
     *     childClassName="Order",
     *     mappedBy="customer"
     * )
     */
    public array $orders = [];
}

// Note: Each class would of course normally be
// in a separate file.

/**
 * @Table(name="order")
 */
class Order
{
    /**
     * @Column(isPrimaryKey=true)
     */ 
    public int $id;
    
    /**
     * @Relationship(
     *     relationshipType="many_to_one",
     *     childClassName="Customer"
     * )
     */
    public Customer $customer;
    
    //... more properties
}

```

{% endtab %}

{% tab title="Doctrine Annotations" %}

```php
use Doctrine\ORM\Mapping as ORM;

/**
 * @ORM\Table(name="customer")
 */
class Customer
{
    /**
     * @ORM\Id
     * @ORM\Column(type="integer")
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    public int $id;
    
    /**
     * @ORM\Column()
     */
    public string $name;
    
    /**
     * @ORM\OneToMany(
     *     targetEntity="Order",
     *     mappedBy="customer"
     * )
     */
    public array $orders = [];
}

// Note: Each class would of course normally be
// in a separate file.

/**
 * @ORM\Table(name="order")
 */
class Order
{
    /**
     * @ORM\Id
     * @ORM\Column(type="integer")
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    public int $id;
    
    /**
     * @ORM\ManyToOne(targetEntity="Customer")
     */
    public Customer $customer;
    
    //... more properties
}

```

{% endtab %}
{% endtabs %}

#### Example 2: Full Mapping

The following example shows all of the mapping information defined, even though some items could be omitted as Objectiphy can guess some of the mapping if it follows standard conventions. You only need to specify all of the mapping information if you are not joining in a standard way from foreign key to primary key, if your foreign key column name is not suffixed with 'id', or the primary key of the target table, or if you need an inner join (note, if using Doctrine annotations, you cannot specify the join type with an annotation). Example 1, above, shows the exact same mapping as this in an abbreviated format.

{% tabs %}
{% tab title="PHP8+ Attributes" %}

```php
use Objectiphy\Objectiphy\Table;
use Objectiphy\Objectiphy\Column;
use Objectiphy\Objectiphy\Relationship;

#[Table(name: 'customer')]
class Customer
{
    #[Column(isPrimaryKey: true)]
    public int $id;
    
    #[Column]
    public string $name;
    
    #[Relationship(
        relationshipType: 'one_to_many',
        childClassName: Order::class,
        mappedBy: 'customer'
    )]
    public array $orders = [];
}

// Note: Each class would of course normally be
// in a separate file.

#[Table(name: 'order')]
class Order
{
    #[Column(isPrimaryKey: true)]
    public int $id;
    
    #[Relationship(
        relationshipType: 'many_to_one',
        childClassName: Customer::class,
        sourceJoinColumn: 'customer_id',
        targetJoinColumn: 'id',
        joinType: 'INNER'
    )]
    public Customer $customer;
    
    //... more properties
}

```

{% endtab %}

{% tab title="Objectiphy Annotations" %}

```php
use Objectiphy\Objectiphy\Table;
use Objectiphy\Objectiphy\Column;
use Objectiphy\Objectiphy\Relationship;

/**
 * @Table(name="customer")
 */
class Customer
{
    /**
     * @Column(isPrimaryKey=true)
     */ 
    public int $id;
    
    /**
     * @Column
     */
    public string $name;
    
    /**
     * @Relationship(
     *     relationshipType="one_to_many",
     *     childClassName="Order",
     *     mappedBy="customer"
     * )
     */
    public array $orders = [];
}

// Note: Each class would of course normally be
// in a separate file.

/**
 * @Table(name="order")
 */
class Order
{
    /**
     * @Column(isPrimaryKey=true)
     */ 
    public int $id;
    
    /**
     * @Relationship(
     *     relationshipType="many_to_one",
     *     childClassName="Customer",
     *     sourceJoinColumn="customer_id",
     *     targetJoinColumn="id",
     *     joinType="INNER"
     * )
     */
    public Customer $customer;
    
    //... more properties
}

```

{% endtab %}

{% tab title="Doctrine Annotations" %}

```php
use Doctrine\ORM\Mapping as ORM;

/**
 * @ORM\Table(name="customer")
 */
class Customer
{
    /**
     * @ORM\Id
     * @ORM\Column(type="integer")
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    public int $id;
    
    /**
     * @ORM\Column()
     */
    public string $name;
    
    /**
     * @ORM\OneToMany(
     *     targetEntity="Order",
     *     mappedBy="customer"
     * )
     */
    public array $orders = [];
}

// Note: Each class would of course normally be
// in a separate file.

/**
 * @ORM\Table(name="order")
 */
class Order
{
    /**
     * @ORM\Id
     * @ORM\Column(type="integer")
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    public int $id;
    
    /**
     * @ORM\ManyToOne(targetEntity="Customer")
     * @ORM\JoinColumn(
     *     name="customer_id",
     *     referencedColumnName="id"
     * )
     */
    public Customer $customer;
    
    //... more properties
}

```

{% endtab %}
{% endtabs %}