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Sets - .NET SDK

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  • Overview
  • Set Types
  • Usage Example
  • Watching For Changes

New in version 10.2.0.

Overview

A Realm set, like the C# HashSet<>, is an implementation of ICollection<> and IEnumerable<>. It supports values of any Realm type except collections. To define a set, use a getter-only ISet<TValue> property, where TValue is any of the supported types.

Deleting an object from the database will remove it from any sets in which it existed. Therefore, a set of objects will never contain null objects. However, sets of primitive types can contain null values. If you do not want to allow null values in a set, then either use non-nullable types in the set declaration (for example, use ISet<double> instead of ISet<double?>). If you are using the older schema type definition (your classes derive from the RealmObject base class), or you do not have nullability enabled, you will need to use the [Required] attribute if the set contains nullable reference types, such as string or byte[].

Important

Not Supported with Sync

Local-only realms support collections of nullable (optional) values, but Sync does not.

Set Types

The following code shows examples of set types:

public partial class Inventory : IRealmObject
{
    // A Set can contain any Realm-supported type, including
    // objects that inherit from RealmObject
    public ISet<Plant> PlantSet { get; }
    public ISet<double> DoubleSet { get; }
    // Nullable types are supported in local-only
    // Realms, but not with Sync
    public ISet<int?> NullableIntsSet { get; }
    public ISet<string> RequiredStrings { get; }
}

Usage Example

The following code shows how to create, write to, and read from Sets.

var inventory = new Inventory();
inventory.PlantSet.Add(new Plant() { Name = "Prickly Pear" });
inventory.DoubleSet.Add(123.45);
realm.Write(() =>
{
    realm.Add<Inventory>(inventory);
});
// convert the Plant Set to an IQueryable and apply a filter
var pricklyPear = inventory.PlantSet.AsRealmQueryable()
    .Where(p => p.Name == "Prickly Pear");
// Alternatively, apply a filter directly on the Plant Set
var pricklyPearPlants = inventory.PlantSet
    .Filter("Name == 'Prickly Pear'");
// Find all Inventory items that have at least one value in their
// DoubleSet that is larger than 5
var moreThan100 = realm.All<Inventory>()
    .Filter("DoubleSet.@values > 100");

Watching For Changes

You can use the INotifyCollectionChanged.CollectionChanged event on a set to watch for changes to the set, and the INotifyPropertyChanged.PropertyChanged event to watch for changes to specific properties in the set.

In the following code example, we have a class with an ISet<string> property named StringSet. We set up event handlers for both the CollectionChanged and PropertyChanged events:

var stringSet = container.StringSet.AsRealmCollection();
stringSet.CollectionChanged += (sender, e) =>
{
    Console.WriteLine($"Set {sender} changed: {e.Action}");
};
stringSet.PropertyChanged += (sender, e) =>
{
    Console.WriteLine($"Property changed on {sender}: {e.PropertyName}");
};
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