One to Many

Join one entity to a collection or array of child entities.

A one-to-many relationship exists where a single parent entity holds an array or collection of child entities of a certain type.

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

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 <-- Foreign key

...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 one-to-many relationship using attributes or annotations (these examples are all equivalent; you only need to use one type of mapping provider, it is up to you which one).

As with one-to-one, 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).

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
}

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.

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
}
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