RLMCollection

@protocol RLMCollection <NSFastEnumeration, RLMThreadConfined>

A homogenous collection of Realm-managed objects. Examples of conforming types include RLMArray, RLMResults, and RLMLinkingObjects.

Properties

  • The number of objects in the collection.

    Declaration

    Objective-C

    @required
@property (readonly, assign, nonatomic) NSUInteger count;
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  • The type of the objects in the collection.

    Declaration

    Objective-C

    @required
@property (readonly, assign, nonatomic) RLMPropertyType type;
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  • Indicates whether the objects in the collection can be nil.

    Declaration

    Objective-C

    @required
@property (readonly, getter=isOptional, nonatomic) BOOL optional;
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  • The class name of the objects contained in the collection.

    Will be nil if type is not RLMPropertyTypeObject.

    Declaration

    Objective-C

    @required
@property (readonly, copy, nonatomic, nullable) NSString *objectClassName;
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  • The Realm which manages the collection, or nil for unmanaged collections.

    Declaration

    Objective-C

    @required
@property (readonly, nonatomic) RLMRealm *_Nonnull realm;
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Accessing Objects from a Collection

  • Returns the object at the index specified.

    Declaration

    Objective-C

    - (nonnull id)objectAtIndex:(NSUInteger)index;

    Parameters

    index

    The index to look up.

    Return Value

    An object of the type contained in the collection.

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  • Returns the first object in the collection.

    Returns nil if called on an empty collection.

    Declaration

    Objective-C

    - (nullable id)firstObject;

    Return Value

    An object of the type contained in the collection.

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  • Returns the last object in the collection.

    Returns nil if called on an empty collection.

    Declaration

    Objective-C

    - (nullable id)lastObject;

    Return Value

    An object of the type contained in the collection.

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Querying a Collection

  • Returns the index of an object in the collection.

    Returns NSNotFound if the object is not found in the collection.

    Declaration

    Objective-C

    - (NSUInteger)indexOfObject:(nonnull id)object;

    Parameters

    object

    An object (of the same type as returned from the objectClassName selector).
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  • Returns the index of the first object in the collection matching the predicate.

    Declaration

    Objective-C

    - (NSUInteger)indexOfObjectWhere:(nonnull NSString *)predicateFormat, ...;

    Parameters

    predicateFormat

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

    Return Value

    The index of the object, or NSNotFound if the object is not found in the collection.

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  • Returns the index of the first object in the collection matching the predicate.

    Declaration

    Objective-C

    - (NSUInteger)indexOfObjectWithPredicate:(nonnull NSPredicate *)predicate;

    Parameters

    predicate

    The predicate with which to filter the objects.

    Return Value

    The index of the object, or NSNotFound if the object is not found in the collection.

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  • Returns all objects matching the given predicate in the collection.

    Declaration

    Objective-C

    - (nonnull RLMResults *)objectsWhere:(nonnull NSString *)predicateFormat, ...;

    Parameters

    predicateFormat

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

    Return Value

    An RLMResults containing objects that match the given predicate.

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  • Returns all objects matching the given predicate in the collection.

    Declaration

    Objective-C

    - (nonnull RLMResults *)objectsWithPredicate:(nonnull NSPredicate *)predicate;

    Parameters

    predicate

    The predicate with which to filter the objects.

    Return Value

    An RLMResults containing objects that match the given predicate.

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  • Returns a sorted RLMResults from the collection.

    Declaration

    Objective-C

    - (nonnull RLMResults *)sortedResultsUsingKeyPath:(nonnull NSString *)keyPath
                                        ascending:(BOOL)ascending;

    Parameters

    keyPath

    The keyPath to sort by.
    ascending

    The direction to sort in.

    Return Value

    An RLMResults sorted by the specified key path.

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  • Returns a sorted RLMResults from the collection.

    Declaration

    Objective-C

    - (nonnull RLMResults *)sortedResultsUsingDescriptors:
    (nonnull NSArray<RLMSortDescriptor *> *)properties;

    Parameters

    properties

    An array of RLMSortDescriptors to sort by.

    Return Value

    An RLMResults sorted by the specified properties.

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  • Returns an NSArray containing the results of invoking valueForKey: using key on each of the collection’s objects.

    Declaration

    Objective-C

    - (nullable id)valueForKey:(nonnull NSString *)key;

    Parameters

    key

    The name of the property.

    Return Value

    An NSArray containing results.

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  • Invokes setValue:forKey: on each of the collection’s objects using the specified value and key.

    Warning

    This method may only be called during a write transaction.

    Declaration

    Objective-C

    - (void)setValue:(nullable id)value forKey:(nonnull NSString *)key;

    Parameters

    value

    The object value.
    key

    The name of the property.
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Notifications

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

    The block will be asynchronously called with the initial collection, 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 will be nil the first time the block is called. For each call after that, it will contain information about which rows in the collection were added, removed or modified. If a write transaction did not modify any objects in this collection, the block is not called at all. See the RLMCollectionChange documentation for information on how the changes are reported and an example of updating a UITableView.

    If an error occurs the block will be called with nil for the collection parameter and a non-nil error. Currently the only errors that can occur are when opening the Realm on the background worker thread.

    At the time when the block is called, the collection object 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 -[RLMRealm 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.

    id<RLMCollection> collection = [Dog allObjects];
NSLog(@"dogs.count: %zu", dogs.count); // => 0
self.token = [collection addNotificationBlock:^(id<RLMCollection> dogs,
                                             RLMCollectionChange *changes,
                                             NSError *error) {
    // Only fired once for the example
    NSLog(@"dogs.count: %zu", dogs.count); // => 1
}];
[realm transactionWithBlock:^{
    Dog *dog = [[Dog alloc] init];
    dog.name = @"Rex";
    [realm addObject:dog];
}];
// end of run loop execution context

    You must retain the returned token for as long as you want updates to continue 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

    Objective-C

    - (nonnull RLMNotificationToken *)addNotificationBlock:
    (nonnull void (^)(id<RLMCollection> _Nullable,
                      RLMCollectionChange *_Nullable, NSError *_Nullable))block;

    Parameters

    block

    The block to be called each time the collection changes.

    Return Value

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

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Aggregating Property Values

  • Returns the minimum (lowest) value of the given property among all the objects in the collection.

    NSNumber *min = [results minOfProperty:@"age"];

    Warning

    You cannot use this method on RLMObject, RLMArray, and NSData properties.

    Declaration

    Objective-C

    - (nullable id)minOfProperty:(nonnull NSString *)property;

    Parameters

    property

    The property whose minimum value is desired. Only properties of types int, float, double, and NSDate are supported.

    Return Value

    The minimum value of the property, or nil if the Results are empty.

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  • Returns the maximum (highest) value of the given property among all the objects in the collection.

    NSNumber *max = [results maxOfProperty:@"age"];

    Warning

    You cannot use this method on RLMObject, RLMArray, and NSData properties.

    Declaration

    Objective-C

    - (nullable id)maxOfProperty:(nonnull NSString *)property;

    Parameters

    property

    The property whose maximum value is desired. Only properties of types int, float, double, and NSDate are supported.

    Return Value

    The maximum value of the property, or nil if the Results are empty.

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

    NSNumber *sum = [results sumOfProperty:@"age"];

    Warning

    You cannot use this method on RLMObject, RLMArray, and NSData properties.

    Declaration

    Objective-C

    - (nonnull NSNumber *)sumOfProperty:(nonnull NSString *)property;

    Parameters

    property

    The property whose values should be summed. Only properties of types int, float, and double are supported.

    Return Value

    The sum of the given property.

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  • Returns the average value of a given property over the objects in the collection.

    NSNumber *average = [results averageOfProperty:@"age"];

    Warning

    You cannot use this method on RLMObject, RLMArray, and NSData properties.

    Declaration

    Objective-C

    - (nullable NSNumber *)averageOfProperty:(nonnull NSString *)property;

    Parameters

    property

    The property whose average value should be calculated. Only properties of types int, float, and double are supported.

    Return Value

    The average value of the given property, or nil if the Results are empty.

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