Relaciones - SDK .NET

To-One Relationship

A to-one relationship means that an object is related in a specific way to no more than one other object. You define a to-one relationship for an object type in its object schema by specifying a property where the type is the related Realm object type.

public partial class Person : IRealmObject
{
    [PrimaryKey]
    [MapTo("_id")]
    public ObjectId Id { get; set; }
    public string Name { get; set; }
    public DateTimeOffset Birthdate { get; set; }
    public Dog? Dog { get; set; }
}
public partial class Dog : IRealmObject
{
    [PrimaryKey]
    [MapTo("_id")]
    public ObjectId Id { get; set; }
    public string Name { get; set; }
    public int Age { get; set; }
    public string Breed { get; set; } = String.Empty;
}

To query a direct relationship, you can use LINQ syntax. See the following example for how to query a one-to-one relationship:

var fidosPerson = realm.All<Person>().FirstOrDefault(p => p.Dog == dog);

Relación de muchos

A to-many relationship means that an object is related in a specific way to multiple objects. You define a to-many relationship for an object type by specifying a property where the type is an IList<T> of the related Realm object type. Define the IList<T> with only a getter. You do not need to initialize it in the constructor, as Realm will generate a collection instance the first time the property is accessed:

// To add items to the IList<T>:
var person = new Person();
person.Dogs.Add(new Dog
{
    Name = "Caleb",
    Age = 7,
    Breed = "mutt"
});

public partial class Person : IRealmObject
{
    [PrimaryKey]
    [MapTo("_id")]
    public ObjectId Id { get; set; }
    public string Name { get; set; }
    public DateTimeOffset Birthdate { get; set; }
    public IList<Dog> Dogs { get; }
}
public partial class Dog : IRealmObject
{
    [PrimaryKey]
    [MapTo("_id")]
    public ObjectId Id { get; set; }
    public string Name { get; set; }
    public int Age { get; set; }
    public string Breed { get; set; } = String.Empty;
}

var katieAndHerDogs = realm.All<Person>().
    Where(p => p.Name == "Katie")
    .FirstOrDefault();

Relación inversa

An inverse relationship links an object back to any other objects that refer to it in a defined to-one or to-many relationship. Relationship definitions are unidirectional, so you must explicitly define a property in the object's model as an inverse relationship.

Por ejemplo, la relación de uno a muchos "un Usuario tiene muchos Elementos" no crea automáticamente la relación inversa "un Elemento pertenece a un Usuario". Si no especificas la relación inversa en el Modelo de objeto, necesitas ejecutar una separate query para buscar al usuario que está asignado a un elemento determinado.

Para definir la relación inversa, defina una IQueryable<T> propiedad solo para captadores en su modelo de objetos, donde T es el tipo de origen de la relación, y luego anote esta propiedad con un atributo [Backlink(sourceProperty)], donde "sourceProperty" es el nombre de la propiedad en el otro lado de la relación. El siguiente ejemplo muestra cómo hacerlo en el escenario "El usuario tiene muchos elementos":

public partial class User : IRealmObject
{
    [PrimaryKey]
    [MapTo("_id")]
    public ObjectId Id { get; set; } = ObjectId.GenerateNewId();
    public string Name { get; set; }
    [Backlink(nameof(Item.Assignee))]
    public IQueryable<Item> Items { get; }
}
public partial class Item : IRealmObject
{
    [PrimaryKey]
    [MapTo("_id")]
    public ObjectId Id { get; set; } = ObjectId.GenerateNewId();
    public string Text { get; set; }
    public User? Assignee { get; set; }
}

In this example, note that:

• The Item object's Assignee property is a User object.

• La propiedad Items del objeto Usuario invierte la relación y hace referencia a todos los objetos Elemento que contienen este Usuario específico en su propiedad Assignee.

This, then, allows us to query the Item collection to get all Items assigned to a specific User.

To query the inverse relationship, you cannot use Linq. Instead, pass a string predicate. The following example shows how you could find all Users who have Items that contain the word "oscillator":

var oscillatorAssignees = realm.All<User>()
    .Filter("Items.Text CONTAINS 'oscillator'").ToList();
foreach (User u in oscillatorAssignees)
{
    Console.WriteLine(u.Name);
}