LinkingObjects
public struct LinkingObjects<Element> where Element : Object
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
-
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Indicates if the linking objects are no longer valid.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 containingrealm
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 }
-
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 }
-
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.
-
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 results of invokingvalueForKey(_:)
withkey
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 invokingvalueForKeyPath(_:)
withkeyPath
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 specifiedvalue
andkey
.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.
-
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
Student
s from youngest to oldest based on theirage
property, you might callstudents.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
SortDescriptor
s 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<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.
-
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 theRealmCollectionChange
documentation for more information on the change information supplied and an example of how to use it to update aUITableView
.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.
let results = realm.objects(Dog.self) 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.
-
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. SeeRealm.Configuration.maximumNumberOfActiveVersions
for more information.Declaration
Swift
public func freeze() -> 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: Publishers.WillChange<LinkingObjects> { get }
-
Returns an iterator that yields successive elements in the linking objects.
Declaration
Swift
public func makeIterator() -> RLMIterator<Element>
-
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