LinkingObjects

public final class LinkingObjects<T: Object>: LinkingObjectsBase

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<T> and Results<T>.

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 Element = T
  • Returns the object at the given index.

    Declaration

    Swift

    public subscript(index: Int) -> T

    Parameters

    index

    The index.

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

    Declaration

    Swift

    public var realm: Realm?
  • Indicates if the linking objects are no longer valid.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
  • The number of linking objects.

    Declaration

    Swift

    public var count: Int
  • 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 type: T.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 override var description: String
  • 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: T) -> 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.

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

    Declaration

    Swift

    public func index(matching predicateFormat: String, _ args: Any...) -> Int?

    Parameters

    predicateFormat

    A predicate format string, optionally followed by a variable number of arguments.

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

    Declaration

    Swift

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

    Declaration

    Swift

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

    Declaration

    Swift

    public override 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 override 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 override 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.

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

    Declaration

    Swift

    public func filter(_ predicateFormat: String, _ args: Any...) -> Results<T>

    Parameters

    predicateFormat

    A predicate format string, optionally followed by a variable number of arguments.

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

    Declaration

    Swift

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

    Parameters

    predicate

    The predicate with which to filter the objects.

  • 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<T>

    Parameters

    keyPath

    The key path to sort by.

    ascending

    The direction to sort in.

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

    Objects are sorted based on the values of the given property. For example, to sort a collection of Students from youngest to oldest based on their age property, you might call students.sorted(byProperty: "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(byProperty property: String, ascending: Bool = true) -> Results<T>

    Parameters

    property

    The name of the property 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<T> where S.Iterator.Element == SortDescriptor

    Parameters

    sortDescriptors

    A sequence of SortDescriptors to sort by.

  • 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<U: MinMaxType>(ofProperty property: String) -> U?

    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<U: MinMaxType>(ofProperty property: String) -> U?

    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<U: AddableType>(ofProperty property: String) -> U

    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<U: AddableType>(ofProperty property: String) -> U?

    Parameters

    property

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

  • 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.

    Notifications are delivered via the standard run loop, and so can’t be delivered while the run loop is blocked by other activity. 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.

    let results = realm.objects(Dog.self)
    print("dogs.count: \(dogs?.count)") // => 0
    let token = dogs.addNotificationBlock { 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 stop() 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 addNotificationBlock(_ block: @escaping (RealmCollectionChange<LinkingObjects>) -> Void) -> NotificationToken

    Parameters

    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.

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

    Declaration

    Swift

    public var startIndex: Int
  • 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
  • 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 func index(after: Int) -> Int

    Parameters

    i

    A valid index of the collection. i must be less than endIndex.

    Return Value

    The index value immediately after i.

  • 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 func index(before: Int) -> Int

    Parameters

    i

    A valid index of the collection. i must be greater than startIndex.

    Return Value

    The index value immediately before i.