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
nilif 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Indicates if the linking objects are no longer valid.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 containingrealminstance.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
typeThe type of the object owning the property the linking objects should refer to.
propertyNameThe 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
nilif the object is not present.Declaration
Swift
public func index(of object: Element) -> Int?Parameters
objectThe object whose index is being queried.
-
Returns the index of the first object matching the given predicate, or
nilif no objects match.Declaration
Swift
public func index(matching predicate: NSPredicate) -> Int?Parameters
predicateThe predicate with which to filter the objects.
-
Returns the index of the first object matching the given predicate, or
nilif no objects match.Declaration
Swift
public func index(matching predicateFormat: String, _ args: Any...) -> Int?Parameters
predicateFormatA predicate format string, optionally followed by a variable number of arguments.
-
Returns the object at the given
index.Declaration
Swift
public subscript(index: Int) -> Element { get }Parameters
indexThe index.
-
Returns the first object in the linking objects, or
nilif the linking objects are empty.Declaration
Swift
public var first: Element? { get } -
Returns the last object in the linking objects, or
nilif the linking objects are empty.Declaration
Swift
public var last: Element? { get }
-
Returns an
Arraycontaining the results of invokingvalueForKey(_:)withkeyon each of the linking objects.Declaration
Swift
public func value(forKey key: String) -> Any?Parameters
keyThe name of the property whose values are desired.
-
Returns an
Arraycontaining the results of invokingvalueForKeyPath(_:)withkeyPathon each of the linking objects.Declaration
Swift
public func value(forKeyPath keyPath: String) -> Any?Parameters
keyPathThe key path to the property whose values are desired.
-
Invokes
setValue(_:forKey:)on each of the linking objects using the specifiedvalueandkey.Warning
This method may only be called during a write transaction.
Declaration
Swift
public func setValue(_ value: Any?, forKey key: String)Parameters
valueThe value to set the property to.
keyThe name of the property whose value should be set on each object.
-
Returns a
Resultscontaining all objects matching the given predicate in the linking objects.Declaration
Swift
public func filter(_ predicateFormat: String, _ args: Any...) -> Results<Element>Parameters
predicateFormatA predicate format string, optionally followed by a variable number of arguments.
-
Returns a
Resultscontaining 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 theirageproperty, 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
keyPathThe key path to sort by.
ascendingThe direction to sort in.
-
Returns a
Resultscontaining 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 == SortDescriptorParameters
sortDescriptorsA sequence of
SortDescriptors to sort by.
-
Returns the minimum (lowest) value of the given property among all the linking objects, or
nilif the linking objects are empty.Warning
Only a property whose type conforms to the
MinMaxTypeprotocol can be specified.Declaration
Swift
public func min<T>(ofProperty property: String) -> T? where T : MinMaxTypeParameters
propertyThe name of a property whose minimum value is desired.
-
Returns the maximum (highest) value of the given property among all the linking objects, or
nilif the linking objects are empty.Warning
Only a property whose type conforms to the
MinMaxTypeprotocol can be specified.Declaration
Swift
public func max<T>(ofProperty property: String) -> T? where T : MinMaxTypeParameters
propertyThe 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
AddableTypeprotocol can be specified.Declaration
Swift
public func sum<T>(ofProperty property: String) -> T where T : AddableTypeParameters
propertyThe name of a property whose values should be summed.
-
Returns the average value of a given property over all the linking objects, or
nilif the linking objects are empty.Warning
Only the name of a property whose type conforms to the
AddableTypeprotocol can be specified.Declaration
Swift
public func average<T>(ofProperty property: String) -> T? where T : AddableTypeParameters
propertyThe 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
changeparameter 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 theRealmCollectionChangedocumentation 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.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.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 contextYou 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(_ block: @escaping (RealmCollectionChange<LinkingObjects>) -> Void) -> NotificationTokenParameters
blockThe 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 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
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LinkingObjects Structure Reference