RLMRealm

@interface RLMRealm : NSObject

An RLMRealm instance (also referred to as a Realm) represents a Realm database.

Realms can either be stored on disk (see +[RLMRealm realmWithURL:]) or in memory (see RLMRealmConfiguration).

RLMRealm instances are cached internally, and constructing equivalent RLMRealm objects (for example, by using the same path or identifier) multiple times on a single thread within a single iteration of the run loop will normally return the same RLMRealm object.

If you specifically want to ensure an RLMRealm instance is destroyed (for example, if you wish to open a Realm, check some property, and then possibly delete the Realm file and re-open it), place the code which uses the Realm within an @autoreleasepool {} and ensure you have no other strong references to it.

Warning

RLMRealm instances are not thread safe and cannot be shared across threads or dispatch queues. Trying to do so will cause an exception to be thrown. You must call this method on each thread you want to interact with the Realm on. For dispatch queues, this means that you must call it in each block which is dispatched, as a queue is not guaranteed to run all of its blocks on the same thread.

Creating & Initializing a Realm

  • Obtains an instance of the default Realm.

    The default Realm is used by the RLMObject class methods which do not take an RLMRealm parameter, but is otherwise not special. The default Realm is persisted as default.realm under the Documents directory of your Application on iOS, and in your application’s Application Support directory on OS X.

    The default Realm is created using the default RLMRealmConfiguration, which can be changed via +[RLMRealmConfiguration setDefaultConfiguration:].

    Declaration

    Objective-C

    + (nonnull instancetype)defaultRealm;

    Swift

    class func `default`() -> Self

    Return Value

    The default RLMRealm instance for the current thread.

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  • Obtains an RLMRealm instance with the given configuration.

    Declaration

    Objective-C

    + (nullable instancetype)
realmWithConfiguration:(nonnull RLMRealmConfiguration *)configuration
                 error:(NSError *_Nullable *_Nullable)error;

    Swift

    convenience init(configuration: RLMRealmConfiguration) throws

    Parameters

    configuration

    A configuration object to use when creating the Realm.
    error

    If an error occurs, upon return contains an NSError object that describes the problem. If you are not interested in possible errors, pass in NULL.

    Return Value

    An RLMRealm instance.

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  • Obtains an RLMRealm instance persisted at a specified file URL.

    Declaration

    Objective-C

    + (nonnull instancetype)realmWithURL:(nonnull NSURL *)fileURL;

    Swift

    convenience init(url fileURL: URL)

    Parameters

    fileURL

    The local URL of the file the Realm should be saved at.

    Return Value

    An RLMRealm instance.

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  • The RLMSchema used by the Realm.

    Declaration

    Objective-C

    @property (readonly, nonatomic) RLMSchema *_Nonnull schema;

    Swift

    var schema: RLMSchema { get }
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  • Indicates if the Realm is currently engaged in a write transaction.

    Warning

    Do not simply check this property and then start a write transaction whenever an object needs to be created, updated, or removed. Doing so might cause a large number of write transactions to be created, degrading performance. Instead, always prefer performing multiple updates during a single transaction.

    Declaration

    Objective-C

    @property (readonly, nonatomic) BOOL inWriteTransaction;

    Swift

    var inWriteTransaction: Bool { get }
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  • The RLMRealmConfiguration object that was used to create this RLMRealm instance.

    Declaration

    Objective-C

    @property (readonly, nonatomic) RLMRealmConfiguration *_Nonnull configuration;

    Swift

    var configuration: RLMRealmConfiguration { get }
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  • Indicates if this Realm contains any objects.

    Declaration

    Objective-C

    @property (readonly, nonatomic) BOOL isEmpty;

    Swift

    var isEmpty: Bool { get }
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Receiving Notification when a Realm Changes

  • Adds a notification handler for changes in this Realm, and returns a notification token.

    Notification handlers are called after each write transaction is committed, either on the current thread or other threads.

    Handler blocks are called on the same thread that they were added on, and may only be added on threads which are currently within a run loop. Unless you are specifically creating and running a run loop on a background thread, this will normally only be the main thread.

    The block has the following definition:

    typedef void(^RLMNotificationBlock)(RLMNotification notification, RLMRealm *realm);

    It receives the following parameters:

    • NSString *notification: The name of the incoming notification. See RLMRealmNotification for information on what notifications are sent.

    • RLMRealm *realm: The Realm for which this notification occurred.

    Declaration

    Objective-C

    - (nonnull RLMNotificationToken *)addNotificationBlock:
    (nonnull RLMNotificationBlock)block;

    Swift

    func addNotificationBlock(_ block: @escaping RLMNotificationBlock) -> RLMNotificationToken

    Parameters

    block

    A block which is called to process Realm notifications.

    Return Value

    A token object which must be retained as long as you wish to continue receiving change notifications.

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Writing to a Realm

  • Begins a write transaction on the Realm.

    Only one write transaction can be open at a time. Write transactions cannot be nested, and trying to begin a write transaction on a Realm which is already in a write transaction will throw an exception. Calls to beginWriteTransaction from RLMRealm instances in other threads will block until the current write transaction completes.

    Before beginning the write transaction, beginWriteTransaction updates the RLMRealm instance to the latest Realm version, as if refresh had been called, and generates notifications if applicable. This has no effect if the Realm was already up to date.

    It is rarely a good idea to have write transactions span multiple cycles of the run loop, but if you do wish to do so you will need to ensure that the Realm participating in the write transaction is kept alive until the write transaction is committed.

    Declaration

    Objective-C

    - (void)beginWriteTransaction;

    Swift

    func beginWriteTransaction()
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  • Commits all write operations in the current write transaction, and ends the transaction.

    Warning

    This method may only be called during a write transaction.

    Declaration

    Objective-C

    - (void)commitWriteTransaction;
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  • Commits all write operations in the current write transaction, and ends the transaction.

    Warning

    This method may only be called during a write transaction.

    Declaration

    Objective-C

    - (BOOL)commitWriteTransaction:(NSError *_Nullable *_Nullable)error;

    Swift

    func commitWriteTransaction() throws

    Parameters

    error

    If an error occurs, upon return contains an NSError object that describes the problem. If you are not interested in possible errors, pass in NULL.

    Return Value

    Whether the transaction succeeded.

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  • Reverts all writes made during the current write transaction and ends the transaction.

    This rolls back all objects in the Realm to the state they were in at the beginning of the write transaction, and then ends the transaction.

    This restores the data for deleted objects, but does not revive invalidated object instances. Any RLMObjects which were added to the Realm will be invalidated rather than becoming unmanaged. Given the following code:

    ObjectType *oldObject = [[ObjectType objectsWhere:@"..."] firstObject];
ObjectType *newObject = [[ObjectType alloc] init];

[realm beginWriteTransaction];
[realm addObject:newObject];
[realm deleteObject:oldObject];
[realm cancelWriteTransaction];

    Both oldObject and newObject will return YES for isInvalidated, but re-running the query which provided oldObject will once again return the valid object.

    Warning

    This method may only be called during a write transaction.

    Declaration

    Objective-C

    - (void)cancelWriteTransaction;

    Swift

    func cancelWriteTransaction()
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  • Performs actions contained within the given block inside a write transaction.

    See

    [RLMRealm transactionWithBlock:error:]

    Declaration

    Objective-C

    - (void)transactionWithBlock:(nonnull void (^)(void))block;
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  • Performs actions contained within the given block inside a write transaction.

    Write transactions cannot be nested, and trying to execute a write transaction on a Realm which is already participating in a write transaction will throw an exception. Calls to transactionWithBlock: from RLMRealm instances in other threads will block until the current write transaction completes.

    Before beginning the write transaction, transactionWithBlock: updates the RLMRealm instance to the latest Realm version, as if refresh had been called, and generates notifications if applicable. This has no effect if the Realm was already up to date.

    Declaration

    Objective-C

    - (BOOL)transactionWithBlock:(nonnull void (^)(void))block
                       error:(NSError *_Nullable *_Nullable)error;

    Swift

    func transaction(_ block: () -> Void) throws

    Parameters

    block

    The block containing actions to perform.
    error

    If an error occurs, upon return contains an NSError object that describes the problem. If you are not interested in possible errors, pass in NULL.

    Return Value

    Whether the transaction succeeded.

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  • Updates the Realm and outstanding objects managed by the Realm to point to the most recent data.

    Declaration

    Objective-C

    - (BOOL)refresh;

    Swift

    func refresh() -> Bool

    Return Value

    Whether there were any updates for the Realm. Note that YES may be returned even if no data actually changed.

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  • Set this property to YES to automatically update this Realm when changes happen in other threads.

    If set to YES (the default), changes made on other threads will be reflected in this Realm on the next cycle of the run loop after the changes are committed. If set to NO, you must manually call -refresh on the Realm to update it to get the latest data.

    Note that by default, background threads do not have an active run loop and you will need to manually call -refresh in order to update to the latest version, even if autorefresh is set to YES.

    Even with this property enabled, you can still call -refresh at any time to update the Realm before the automatic refresh would occur.

    Notifications are sent when a write transaction is committed whether or not automatic refreshing is enabled.

    Disabling autorefresh on a Realm without any strong references to it will not have any effect, and autorefresh will revert back to YES the next time the Realm is created. This is normally irrelevant as it means that there is nothing to refresh (as managed RLMObjects, RLMArrays, and RLMResults have strong references to the Realm that manages them), but it means that setting RLMRealm.defaultRealm.autorefresh = NO in application:didFinishLaunchingWithOptions: and only later storing Realm objects will not work.

    Defaults to YES.

    Declaration

    Objective-C

    @property (assign, readwrite, nonatomic) BOOL autorefresh;

    Swift

    var autorefresh: Bool { get set }
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  • Writes a compacted and optionally encrypted copy of the Realm to the given local URL.

    The destination file cannot already exist.

    Note that if this method is called from within a write transaction, the current data is written, not the data from the point when the previous write transaction was committed.

    Declaration

    Objective-C

    - (BOOL)writeCopyToURL:(nonnull NSURL *)fileURL
         encryptionKey:(nullable NSData *)key
                 error:(NSError *_Nullable *_Nullable)error;

    Swift

    func writeCopy(to fileURL: URL, encryptionKey key: Data?) throws

    Parameters

    fileURL

    Local URL to save the Realm to.
    key

    Optional 64-byte encryption key to encrypt the new file with.
    error

    If an error occurs, upon return contains an NSError object that describes the problem. If you are not interested in possible errors, pass in NULL.

    Return Value

    YES if the Realm was successfully written to disk, NO if an error occurred.

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  • Invalidates all RLMObjects, RLMResults, RLMLinkingObjects, and RLMArrays managed by the Realm.

    A Realm holds a read lock on the version of the data accessed by it, so that changes made to the Realm on different threads do not modify or delete the data seen by this Realm. Calling this method releases the read lock, allowing the space used on disk to be reused by later write transactions rather than growing the file. This method should be called before performing long blocking operations on a background thread on which you previously read data from the Realm which you no longer need.

    All RLMObject, RLMResults and RLMArray instances obtained from this RLMRealm instance on the current thread are invalidated. RLMObjects and RLMArrays cannot be used. RLMResults will become empty. The Realm itself remains valid, and a new read transaction is implicitly begun the next time data is read from the Realm.

    Calling this method multiple times in a row without reading any data from the Realm, or before ever reading any data from the Realm, is a no-op. This method may not be called on a read-only Realm.

    Declaration

    Objective-C

    - (void)invalidate;

    Swift

    func invalidate()
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Adding and Removing Objects from a Realm

  • Adds an object to the Realm.

    Once added, this object is considered to be managed by the Realm. It can be retrieved using the objectsWhere: selectors on RLMRealm and on subclasses of RLMObject.

    When added, all child relationships referenced by this object will also be added to the Realm if they are not already in it.

    If the object or any related objects are already being managed by a different Realm an exception will be thrown. Use -[RLMObject createInRealm:withObject:] to insert a copy of a managed object into a different Realm.

    The object to be added must be valid and cannot have been previously deleted from a Realm (i.e. isInvalidated must be NO).

    Warning

    This method may only be called during a write transaction.

    Declaration

    Objective-C

    - (void)addObject:(nonnull RLMObject *)object;

    Swift

    func add(_ object: RLMObject)

    Parameters

    object

    The object to be added to this Realm.
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  • Adds all the objects in a collection to the Realm.

    This is the equivalent of calling addObject: for every object in a collection.

    Warning

    This method may only be called during a write transaction.

    See

    addObject:

    Declaration

    Objective-C

    - (void)addObjects:(nonnull id<NSFastEnumeration>)array;

    Swift

    func addObjects(_ array: NSFastEnumeration)

    Parameters

    array

    An enumerable object such as NSArray or RLMResults which contains objects to be added to the Realm.
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  • Adds or updates an existing object into the Realm.

    The object provided must have a designated primary key. If no objects exist in the Realm with the same primary key value, the object is inserted. Otherwise, the existing object is updated with any changed values.

    As with addObject:, the object cannot already be managed by a different Realm. Use -[RLMObject createOrUpdateInRealm:withValue:] to copy values to a different Realm.

    Warning

    This method may only be called during a write transaction.

    Declaration

    Objective-C

    - (void)addOrUpdateObject:(nonnull RLMObject *)object;

    Swift

    func addOrUpdate(_ object: RLMObject)

    Parameters

    object

    The object to be added or updated.
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  • Adds or updates all the objects in a collection into the Realm.

    This is the equivalent of calling addOrUpdateObject: for every object in a collection.

    Warning

    This method may only be called during a write transaction.

    See

    addOrUpdateObject:

    Declaration

    Objective-C

    - (void)addOrUpdateObjectsFromArray:(nonnull id)array;

    Swift

    func addOrUpdateObjects(fromArray array: Any)

    Parameters

    array

    An NSArray, RLMArray, or RLMResults of RLMObjects (or subclasses) to be added to the Realm.
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  • Deletes an object from the Realm. Once the object is deleted it is considered invalidated.

    Warning

    This method may only be called during a write transaction.

    Declaration

    Objective-C

    - (void)deleteObject:(nonnull RLMObject *)object;

    Swift

    func delete(_ object: RLMObject)

    Parameters

    object

    The object to be deleted.
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  • Deletes one or more objects from the Realm.

    This is the equivalent of calling deleteObject: for every object in a collection.

    Warning

    This method may only be called during a write transaction.

    See

    deleteObject:

    Declaration

    Objective-C

    - (void)deleteObjects:(nonnull id)array;

    Swift

    func deleteObjects(_ array: Any)

    Parameters

    array

    An RLMArray, NSArray, or RLMResults of RLMObjects (or subclasses) to be deleted.
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  • Deletes all objects from the Realm.

    Warning

    This method may only be called during a write transaction.

    See

    deleteObject:

    Declaration

    Objective-C

    - (void)deleteAllObjects;

    Swift

    func deleteAllObjects()
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Migrations

  • Returns the schema version for a Realm at a given local URL.

    Declaration

    Objective-C

    + (uint64_t)schemaVersionAtURL:(nonnull NSURL *)fileURL
                 encryptionKey:(nullable NSData *)key
                         error:(NSError *_Nullable *_Nullable)error;

    Swift

    class func __schemaVersion(at fileURL: URL, encryptionKey key: Data?, error: NSErrorPointer) -> UInt64

    Parameters

    fileURL

    Local URL to a Realm file.
    key

    64-byte key used to encrypt the file, or nil if it is unencrypted.
    error

    If an error occurs, upon return contains an NSError object that describes the problem. If you are not interested in possible errors, pass in NULL.

    Return Value

    The version of the Realm at fileURL, or RLMNotVersioned if the version cannot be read.

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  • Performs the given Realm configuration’s migration block on a Realm at the given path.

    This method is called automatically when opening a Realm for the first time and does not need to be called explicitly. You can choose to call this method to control exactly when and how migrations are performed.

    See

    RLMMigration

    Declaration

    Objective-C

    + (nullable NSError *)migrateRealm:
    (nonnull RLMRealmConfiguration *)configuration;

    Swift

    class func __migrateRealm(_ configuration: RLMRealmConfiguration) -> Error?

    Parameters

    configuration

    The Realm configuration used to open and migrate the Realm.

    Return Value

    The error that occurred while applying the migration, if any.

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  • Performs the given Realm configuration’s migration block on a Realm at the given path.

    This method is called automatically when opening a Realm for the first time and does not need to be called explicitly. You can choose to call this method to control exactly when and how migrations are performed.

    See

    RLMMigration

    Declaration

    Objective-C

    + (BOOL)performMigrationForConfiguration:
            (nonnull RLMRealmConfiguration *)configuration
                                   error:(NSError *_Nullable *_Nullable)error;

    Swift

    class func performMigration(for configuration: RLMRealmConfiguration) throws

    Parameters

    configuration

    The Realm configuration used to open and migrate the Realm.

    Return Value

    The error that occurred while applying the migration, if any.

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