LinkingObjects

@frozen
public struct LinkingObjects<Element> where Element : RLMObjectBase, Element : RealmCollectionValue
extension LinkingObjects: RealmSubscribable
extension LinkingObjects: RealmCollection
extension LinkingObjects: LinkingObjectsProtocol

LinkingObjects is an auto-updating container type. It represents zero or more objects that are linked to its owning model object through a property relationship.

LinkingObjects can be queried with the same predicates as List<Element> and Results<Element>.

LinkingObjects always reflects the current state of the Realm on the current thread, including during write transactions on the current thread. The one exception to this is when using for...in enumeration, which will always enumerate over the linking objects that were present when the enumeration is begun, even if some of them are deleted or modified to no longer link to the target object during the enumeration.

LinkingObjects can only be used as a property on Object models. Properties of this type must be declared as let and cannot be dynamic.

  • The type of the objects represented by the linking objects.

    Declaration

    Swift

    public typealias ElementType = Element

Properties

  • The Realm which manages the linking objects, or nil if the linking objects are unmanaged.

    Declaration

    Swift

    public var realm: Realm? { get }
  • Indicates if the linking objects are no longer valid.

    The linking objects become invalid if invalidate() is called on the containing realm instance.

    An invalidated linking objects can be accessed, but will always be empty.

    Declaration

    Swift

    public var isInvalidated: Bool { get }
  • The number of linking objects.

    Declaration

    Swift

    public var count: Int { get }

Initializers

  • Creates an instance of a LinkingObjects. This initializer should only be called when declaring a property on a Realm model.

    Declaration

    Swift

    public init(fromType _: Element.Type, property propertyName: String)

    Parameters

    type

    The type of the object owning the property the linking objects should refer to.

    propertyName

    The property name of the property the linking objects should refer to.

  • A human-readable description of the objects represented by the linking objects.

    Declaration

    Swift

    public var description: String { get }

Index Retrieval

  • Returns the index of an object in the linking objects, or nil if the object is not present.

    Declaration

    Swift

    public func index(of object: Element) -> Int?

    Parameters

    object

    The object whose index is being queried.

  • Returns the index of the first object matching the given predicate, or nil if no objects match.

    Declaration

    Swift

    public func index(matching predicate: NSPredicate) -> Int?

    Parameters

    predicate

    The predicate with which to filter the objects.

Object Retrieval

  • Returns the object at the given index.

    Declaration

    Swift

    public subscript(index: Int) -> Element { get }

    Parameters

    index

    The index.

  • Returns the first object in the linking objects, or nil if the linking objects are empty.

    Declaration

    Swift

    public var first: Element? { get }
  • Returns the last object in the linking objects, or nil if the linking objects are empty.

    Declaration

    Swift

    public var last: Element? { get }
  • Returns an array containing the objects in the linking objects at the indexes specified by a given index set.

    Warning

    warning Throws if an index supplied in the IndexSet is out of bounds.

    Declaration

    Swift

    public func objects(at indexes: IndexSet) -> [Element]

    Parameters

    indexes

    The indexes in the linking objects to select objects from.

KVC

  • Returns an Array containing the results of invoking valueForKey(_:) with key on each of the linking objects.

    Declaration

    Swift

    public func value(forKey key: String) -> Any?

    Parameters

    key

    The name of the property whose values are desired.

  • Returns an Array containing the results of invoking valueForKeyPath(_:) with keyPath on each of the linking objects.

    Declaration

    Swift

    public func value(forKeyPath keyPath: String) -> Any?

    Parameters

    keyPath

    The key path to the property whose values are desired.

  • Invokes setValue(_:forKey:) on each of the linking objects using the specified value and key.

    Warning

    This method may only be called during a write transaction.

    Declaration

    Swift

    public func setValue(_ value: Any?, forKey key: String)

    Parameters

    value

    The value to set the property to.

    key

    The name of the property whose value should be set on each object.

Filtering

  • Returns a Results containing all objects matching the given predicate in the linking objects.

    Declaration

    Swift

    public func filter(_ predicate: NSPredicate) -> Results<Element>

    Parameters

    predicate

    The predicate with which to filter the objects.

Sorting

  • Returns a Results containing all the linking objects, but sorted.

    Objects are sorted based on the values of the given key path. For example, to sort a collection of Students from youngest to oldest based on their age property, you might call students.sorted(byKeyPath: "age", ascending: true).

    Warning

    Collections may only be sorted by properties of boolean, Date, NSDate, single and double-precision floating point, integer, and string types.

    Declaration

    Swift

    public func sorted(byKeyPath keyPath: String, ascending: Bool = true) -> Results<Element>

    Parameters

    keyPath

    The key path to sort by.

    ascending

    The direction to sort in.

  • Returns a Results containing all the linking objects, but sorted.

    Warning

    Collections may only be sorted by properties of boolean, Date, NSDate, single and double-precision floating point, integer, and string types.

    Declaration

    Swift

    public func sorted<S: Sequence>(by sortDescriptors: S) -> Results<Element>
        where S.Iterator.Element == SortDescriptor

    Parameters

    sortDescriptors

    A sequence of SortDescriptors to sort by.

Aggregate Operations

  • Returns the minimum (lowest) value of the given property among all the linking objects, or nil if the linking objects are empty.

    Warning

    Only a property whose type conforms to the MinMaxType protocol can be specified.

    Declaration

    Swift

    public func min<T>(ofProperty property: String) -> T? where T : MinMaxType

    Parameters

    property

    The name of a property whose minimum value is desired.

  • Returns the maximum (highest) value of the given property among all the linking objects, or nil if the linking objects are empty.

    Warning

    Only a property whose type conforms to the MinMaxType protocol can be specified.

    Declaration

    Swift

    public func max<T>(ofProperty property: String) -> T? where T : MinMaxType

    Parameters

    property

    The name of a property whose minimum value is desired.

  • Returns the sum of the values of a given property over all the linking objects.

    Warning

    Only a property whose type conforms to the AddableType protocol can be specified.

    Declaration

    Swift

    public func sum<T>(ofProperty property: String) -> T where T : AddableType

    Parameters

    property

    The name of a property whose values should be summed.

  • Returns the average value of a given property over all the linking objects, or nil if the linking objects are empty.

    Warning

    Only the name of a property whose type conforms to the AddableType protocol can be specified.

    Declaration

    Swift

    public func average<T>(ofProperty property: String) -> T? where T : AddableType

    Parameters

    property

    The name of a property whose average value should be calculated.

Notifications

  • Registers a block to be called each time the collection changes.

    The block will be asynchronously called with the initial results, and then called again after each write transaction which changes either any of the objects in the collection, or which objects are in the collection.

    The change parameter that is passed to the block reports, in the form of indices within the collection, which of the objects were added, removed, or modified during each write transaction. See the RealmCollectionChange documentation for more information on the change information supplied and an example of how to use it to update a UITableView.

    At the time when the block is called, the collection will be fully evaluated and up-to-date, and as long as you do not perform a write transaction on the same thread or explicitly call realm.refresh(), accessing it will never perform blocking work.

    If no queue is given, notifications are delivered via the standard run loop, and so can’t be delivered while the run loop is blocked by other activity. If a queue is given, notifications are delivered to that queue instead. When notifications can’t be delivered instantly, multiple notifications may be coalesced into a single notification. This can include the notification with the initial collection.

    For example, the following code performs a write transaction immediately after adding the notification block, so there is no opportunity for the initial notification to be delivered first. As a result, the initial notification will reflect the state of the Realm after the write transaction.

    class Person: Object {
        @Persisted(originProperty: "handlers")
        var dogs: LinkingObjects<Dog>
    }
    class Dog: Object {
        @Persisted var name: String
        @Persisted var handlers: List<Person>
    }
    // ...
    let dogs = person.dogs
    print("dogs.count: \(dogs?.count)") // => 0
    let token = dogs.observe { changes in
        switch changes {
        case .initial(let dogs):
            // Will print "dogs.count: 1"
            print("dogs.count: \(dogs.count)")
            break
        case .update:
            // Will not be hit in this example
            break
        case .error:
            break
        }
    }
    try! realm.write {
        let dog = Dog()
        dog.name = "Rex"
        person.dogs.append(dog)
    }
    // end of run loop execution context
    

    You must retain the returned token for as long as you want updates to be sent to the block. To stop receiving updates, call invalidate() on the token.

    Warning

    This method cannot be called during a write transaction, or when the containing Realm is read-only.

    Declaration

    Swift

    public func observe(on queue: DispatchQueue? = nil,
                        _ block: @escaping (RealmCollectionChange<LinkingObjects>) -> Void) -> NotificationToken

    Parameters

    queue

    The serial dispatch queue to receive notification on. If nil, notifications are delivered to the current thread.

    block

    The block to be called whenever a change occurs.

    Return Value

    A token which must be held for as long as you want updates to be delivered.

  • Registers a block to be called each time the collection changes.

    The block will be asynchronously called with the initial results, and then called again after each write transaction which changes either any of the objects in the collection, or which objects are in the collection.

    The change parameter that is passed to the block reports, in the form of indices within the collection, which of the objects were added, removed, or modified during each write transaction. See the RealmCollectionChange documentation for more information on the change information supplied and an example of how to use it to update a UITableView.

    At the time when the block is called, the collection will be fully evaluated and up-to-date, and as long as you do not perform a write transaction on the same thread or explicitly call realm.refresh(), accessing it will never perform blocking work.

    If no queue is given, notifications are delivered via the standard run loop, and so can’t be delivered while the run loop is blocked by other activity. If a queue is given, notifications are delivered to that queue instead. When notifications can’t be delivered instantly, multiple notifications may be coalesced into a single notification. This can include the notification with the initial collection.

    For example, the following code performs a write transaction immediately after adding the notification block, so there is no opportunity for the initial notification to be delivered first. As a result, the initial notification will reflect the state of the Realm after the write transaction.

    class Person: Object {
        @Persisted(originProperty: "handlers")
        var dogs: LinkingObjects<Dog>
    }
    class Dog: Object {
        @Persisted var name: String
        @Persisted var handlers: List<Person>
    }
    // ...
    let dogs = person.dogs
    print("dogs.count: \(dogs?.count)") // => 0
    let token = dogs.observe { changes in
        switch changes {
        case .initial(let dogs):
            // Will print "dogs.count: 1"
            print("dogs.count: \(dogs.count)")
            break
        case .update:
            // Will not be hit in this example
            break
        case .error:
            break
        }
    }
    try! realm.write {
        let dog = Dog()
        dog.name = "Rex"
        person.dogs.append(dog)
    }
    // end of run loop execution context
    

    If no key paths are given, the block will be executed on any insertion, modification, or deletion for all object properties and the properties of any nested, linked objects. If a key path or key paths are provided, then the block will be called for changes which occur only on the provided key paths. For example, if:

    class Person: Object {
        @Persisted(originProperty: "handlers")
        var dogs: LinkingObjects<Dog>
    }
    class Dog: Object {
        @Persisted var name: String
        @Persisted var age: Int
        @Persisted var toys: List<Toy>
        @Persisted var handlers: List<Person>
    }
    // ...
    let dogs = person.dogs
    let token = dogs.observe(keyPaths: ["name"]) { changes in
        switch changes {
        case .initial(let dogs):
           // ...
        case .update:
           // This case is hit:
           // - after the token is intialized
           // - when the name property of an object in the
           // collection is modified
           // - when an element is inserted or removed
           //   from the collection.
           // This block is not triggered:
           // - when a value other than name is modified on
           //   one of the elements.
        case .error:
            // ...
        }
    }
    // end of run loop execution context
    
    • If the observed key path were ["toys.brand"], then any insertion or deletion to the toys list on any of the collection’s elements would trigger the block. Changes to the brand value on any Toy that is linked to a Dog in this collection will trigger the block. Changes to a value other than brand on any Toy that is linked to a Dog in this collection would not trigger the block. Any insertion or removal to the Dog type collection being observed would also trigger a notification.
    • If the above example observed the ["toys"] key path, then any insertion, deletion, or modification to the toys list for any element in the collection would trigger the block. Changes to any value on any Toy that is linked to a Dog in this collection would not trigger the block. Any insertion or removal to the Dog type collection being observed would still trigger a notification.

    Note

    Multiple notification tokens on the same object which filter for separate key paths do not filter exclusively. If one key path change is satisfied for one notification token, then all notification token blocks for that object will execute.

    You must retain the returned token for as long as you want updates to be sent to the block. To stop receiving updates, call invalidate() on the token.

    Warning

    This method cannot be called during a write transaction, or when the containing Realm is read-only.

    Declaration

    Swift

    public func observe(keyPaths: [String]? = nil,
                        on queue: DispatchQueue? = nil,
                        _ block: @escaping (RealmCollectionChange<LinkingObjects>) -> Void) -> NotificationToken

    Parameters

    keyPaths

    Only properties contained in the key paths array will trigger the block when they are modified. If nil, notifications will be delivered for any property change on the object. String key paths which do not correspond to a valid a property will throw an exception. See description above for more detail on linked properties.

    queue

    The serial dispatch queue to receive notification on. If nil, notifications are delivered to the current thread.

    block

    The block to be called whenever a change occurs.

    Return Value

    A token which must be held for as long as you want updates to be delivered.

  • Registers a block to be called each time the collection changes.

    The block will be asynchronously called with the initial results, and then called again after each write transaction which changes either any of the objects in the collection, or which objects are in the collection.

    The change parameter that is passed to the block reports, in the form of indices within the collection, which of the objects were added, removed, or modified during each write transaction. See the RealmCollectionChange documentation for more information on the change information supplied and an example of how to use it to update a UITableView.

    At the time when the block is called, the collection will be fully evaluated and up-to-date, and as long as you do not perform a write transaction on the same thread or explicitly call realm.refresh(), accessing it will never perform blocking work.

    If no queue is given, notifications are delivered via the standard run loop, and so can’t be delivered while the run loop is blocked by other activity. If a queue is given, notifications are delivered to that queue instead. When notifications can’t be delivered instantly, multiple notifications may be coalesced into a single notification. This can include the notification with the initial collection.

    For example, the following code performs a write transaction immediately after adding the notification block, so there is no opportunity for the initial notification to be delivered first. As a result, the initial notification will reflect the state of the Realm after the write transaction.

    class Person: Object {
        @Persisted(originProperty: "handlers")
        var dogs: LinkingObjects<Dog>
    }
    class Dog: Object {
        @Persisted var name: String
        @Persisted var handlers: List<Person>
    }
    // ...
    let dogs = person.dogs
    print("dogs.count: \(dogs?.count)") // => 0
    let token = dogs.observe { changes in
        switch changes {
        case .initial(let dogs):
            // Will print "dogs.count: 1"
            print("dogs.count: \(dogs.count)")
            break
        case .update:
            // Will not be hit in this example
            break
        case .error:
            break
        }
    }
    try! realm.write {
        let dog = Dog()
        dog.name = "Rex"
        person.dogs.append(dog)
    }
    // end of run loop execution context
    

    If no key paths are given, the block will be executed on any insertion, modification, or deletion for all object properties and the properties of any nested, linked objects. If a key path or key paths are provided, then the block will be called for changes which occur only on the provided key paths. For example, if:

    class Person: Object {
        @Persisted(originProperty: "handlers")
        var dogs: LinkingObjects<Dog>
    }
    class Dog: Object {
        @Persisted var name: String
        @Persisted var age: Int
        @Persisted var toys: List<Toy>
        @Persisted var handlers: List<Person>
    }
    // ...
    let dogs = person.dogs
    let token = dogs.observe(keyPaths: [\Dog.name]) { changes in
        switch changes {
        case .initial(let dogs):
           // ...
        case .update:
           // This case is hit:
           // - after the token is intialized
           // - when the name property of an object in the
           // collection is modified
           // - when an element is inserted or removed
           //   from the collection.
           // This block is not triggered:
           // - when a value other than name is modified on
           //   one of the elements.
        case .error:
            // ...
        }
    }
    // end of run loop execution context
    
    • If the observed key path were [\Dog.toys.brand], then any insertion or deletion to the toys list on any of the collection’s elements would trigger the block. Changes to the brand value on any Toy that is linked to a Dog in this collection will trigger the block. Changes to a value other than brand on any Toy that is linked to a Dog in this collection would not trigger the block. Any insertion or removal to the Dog type collection being observed would also trigger a notification.
    • If the above example observed the [\Dog.toys] key path, then any insertion, deletion, or modification to the toys list for any element in the collection would trigger the block. Changes to any value on any Toy that is linked to a Dog in this collection would not trigger the block. Any insertion or removal to the Dog type collection being observed would still trigger a notification.

    Note

    Multiple notification tokens on the same object which filter for separate key paths do not filter exclusively. If one key path change is satisfied for one notification token, then all notification token blocks for that object will execute.

    You must retain the returned token for as long as you want updates to be sent to the block. To stop receiving updates, call invalidate() on the token.

    Warning

    This method cannot be called during a write transaction, or when the containing Realm is read-only.

    Declaration

    Swift

    public func observe<T: ObjectBase>(keyPaths: [PartialKeyPath<T>],
                                       on queue: DispatchQueue? = nil,
                                       _ block: @escaping (RealmCollectionChange<LinkingObjects>) -> Void) -> NotificationToken

    Parameters

    keyPaths

    Only properties contained in the key paths array will trigger the block when they are modified. If nil, notifications will be delivered for any property change on the object. See description above for more detail on linked properties.

    queue

    The serial dispatch queue to receive notification on. If nil, notifications are delivered to the current thread.

    block

    The block to be called whenever a change occurs.

    Return Value

    A token which must be held for as long as you want updates to be delivered.

Frozen Objects

  • Returns if this collection is frozen.

    Declaration

    Swift

    public var isFrozen: Bool { get }
  • Returns a frozen (immutable) snapshot of this collection.

    The frozen copy is an immutable collection which contains the same data as this collection currently contains, but will not update when writes are made to the containing Realm. Unlike live collections, frozen collections can be accessed from any thread.

    Warning

    This method cannot be called during a write transaction, or when the containing Realm is read-only.

    Warning

    Holding onto a frozen collection for an extended period while performing write transaction on the Realm may result in the Realm file growing to large sizes. See Realm.Configuration.maximumNumberOfActiveVersions for more information.

    Declaration

    Swift

    public func freeze() -> LinkingObjects
  • Returns a live version of this frozen collection.

    This method resolves a reference to a live copy of the same frozen collection. If called on a live collection, will return itself.

    Declaration

    Swift

    public func thaw() -> LinkingObjects<Element>?

LinkingObjects

  • A publisher that emits Void each time the collection changes.

    Despite the name, this actually emits after the collection has changed.

    Declaration

    Swift

    public var objectWillChange: RealmPublishers.WillChange<LinkingObjects> { get }

Sequence Support

Collection Support

  • The position of the first element in a non-empty collection. Identical to endIndex in an empty collection.

    Declaration

    Swift

    public var startIndex: Int { get }
  • The collection’s “past the end” position. endIndex is not a valid argument to subscript, and is always reachable from startIndex by zero or more applications of successor().

    Declaration

    Swift

    public var endIndex: Int { get }
  • Declaration

    Swift

    public func index(after: Int) -> Int
  • Declaration

    Swift

    public func index(before: Int) -> Int