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NSPersistentStoreCoordinator Class Reference

Overview

Instances of NSPersistentStoreCoordinator associate persistent stores (by type) with a model (or more accurately, a configuration of a model) and serve to mediate between the persistent store or stores and the managed object context or contexts. Instances of NSManagedObjectContext use a coordinator to save object graphs to persistent storage and to retrieve model information. A context without a coordinator is not fully functional as it cannot access a model except through a coordinator. The coordinator is designed to present a façade to the managed object contexts such that a group of persistent stores appears as an aggregate store. A managed object context can then create an object graph based on the union of all the data stores the coordinator covers.

Coordinators do the opposite of providing for concurrency—they serialize operations. If you want to use multiple threads for different write operations you use multiple coordinators. Note that if multiple threads work directly with a coordinator, they need to lock and unlock it explicitly.

Each coordinator (and thus container) may use different copies, and hence different versions, of a managed object model. This allows you to cleanly deal with file versioning.

The coordinator gives access to its underlying object stores. You can retrieve an object store when you first add one (using addPersistentStoreWithType:configuration:URL:options:error:), or by using persistentStoreForURL: or persistentStores. This allows you to to determine, for example, whether a store has already been added, or whether two objects come from the same store.

• You move a store from one location to another, or change the type of a store, using migratePersistentStore:toURL:options:withType:error:.

• You can set metadata for a given store using the persistent store coordinator (setMetadata:forPersistentStore:).

For more details about these tasks, see Persistent Stores.

Tasks

Registered Store Types

• + registeredStoreTypes
• + registerStoreClass:forStoreType:

Initializing

• – initWithManagedObjectModel:
• – managedObjectModel

Configuring Persistent Stores

• – addPersistentStoreWithType:configuration:URL:options:error:
• – setURL:forPersistentStore:
• – removePersistentStore:error:
• – migratePersistentStore:toURL:options:withType:error:
• – persistentStores
• – persistentStoreForURL:
• – URLForPersistentStore:

Locking

• – lock
• – tryLock
• – unlock

Working with Metadata

• – metadataForPersistentStore:
• – setMetadata:forPersistentStore:
• + setMetadata:forPersistentStoreOfType:URL:error:
• + metadataForPersistentStoreOfType:URL:error:
• + metadataForPersistentStoreWithURL:error: Deprecated in Mac OS X v10.5

Discovering Object IDs

• – managedObjectIDForURIRepresentation:

Class Methods

metadataForPersistentStoreOfType:URL:error:

Returns a dictionary containing the metadata stored in the persistent store at a given URL.

+ (NSDictionary *)metadataForPersistentStoreOfType:(NSString *)storeType URL:(NSURL *)url error:(NSError **)error

Parameters

storeType

The type of the store at url. If this value is nil, Core Data determines which store class should be used to get or set the store file's metadata by inspecting the file contents.

url

The location of a persistent store.

error

If no store is found at url or if there is a problem accessing its contents, upon return contains an NSError object that describes the problem.

Return Value

A dictionary containing the metadata stored in the persistent store at url, or nil if the store cannot be opened or if there is a problem accessing its contents.

The keys guaranteed to be in this dictionary are NSStoreTypeKey and NSStoreUUIDKey.

Discussion

You can use this method to retrieve the metadata from a store without the overhead of creating a Core Data stack.

Availability

• Available in Mac OS X v10.5 and later.

See Also

• + setMetadata:forPersistentStoreOfType:URL:error:
• – metadataForPersistentStore:
• – setMetadata:forPersistentStore:

Declared In

NSPersistentStoreCoordinator.h

registeredStoreTypes

Returns a dictionary of the registered store types.

+ (NSDictionary *)registeredStoreTypes

Return Value

A dictionary of the registered store types—the keys are the store type strings, and the values are the NSPersistentStore subclasses.

Availability

• Available in Mac OS X v10.5 and later.

Declared In

NSPersistentStoreCoordinator.h

registerStoreClass:forStoreType:

Registers a given NSPersistentStore subclass for a given store type string.

+ (void)registerStoreClass:(Class)storeClass forStoreType:(NSString *)storeType

Parameters

storeClass

The NSPersistentStore subclass to use for the store of type storeType.

storeType

A unique string that identifies a store type.

Discussion

You must invoke this method before a custom subclass of NSPersistentStore can be loaded into a persistent store coordinator.

You can pass nil for storeClass to unregister the store type.

Availability

• Available in Mac OS X v10.5 and later.

Declared In

NSPersistentStoreCoordinator.h

setMetadata:forPersistentStoreOfType:URL:error:

Sets the metadata for a given store.

+ (BOOL)setMetadata:(NSDictionary *)metadata forPersistentStoreOfType:(NSString *)storeType URL:(NSURL *)url error:(NSError **)error

Parameters

metadata

A dictionary containing metadata for the store.

storeType

The type of the store at url. If this value is nil, Core Data will determine which store class should be used to get or set the store file's metadata by inspecting the file contents.

url

The location of a persistent store.

error

If no store is found at url or if there is a problem setting its metadata, upon return contains an NSError object that describes the problem.

Return Value

YES if the metadata was set correctly, otherwise NO.

Discussion

You can use this method to set the metadata for a store without the overhead of creating a Core Data stack.

Availability

• Available in Mac OS X v10.5 and later.

See Also

• + metadataForPersistentStoreOfType:URL:error:
• – metadataForPersistentStore:
• – setMetadata:forPersistentStore:

Declared In

NSPersistentStoreCoordinator.h

Instance Methods

addPersistentStoreWithType:configuration:URL:options:error:

Adds a new persistent store of a specified type at a given location, and returns the new store.

- (NSPersistentStore *)addPersistentStoreWithType:(NSString *)storeType configuration:(NSString *)configuration URL:(NSURL *)storeURL options:(NSDictionary *)options error:(NSError **)error

Parameters

storeType

A string constant (such as NSSQLiteStoreType) that specifies the store type—see “Store Types” for possible values.

configuration

The name of a configuration in the receiver's managed object model that will be used by the new store. The configuration can be nil, in which case no other configurations are allowed.

storeURL

The file location of the persistent store.

options

A dictionary containing key-value pairs that specify whether the store should be read-only, and whether (for an XML store) the XML file should be validated against the DTD before it is read. For key definitions, see “Migration Options”. This value may be nil.

error

If a new store cannot be created, upon return contains an instance of NSError that describes the problem

Return Value

The newly-created store or, if an error occurs, nil.

Availability

• Available in Mac OS X v10.4 and later.

See Also

• – migratePersistentStore:toURL:options:withType:error:
• – removePersistentStore:error:

Declared In

NSPersistentStoreCoordinator.h

initWithManagedObjectModel:

Initializes the receiver with a managed object model.

- (id)initWithManagedObjectModel:(NSManagedObjectModel *)model

Parameters

model

A managed object model.

Return Value

The receiver, initialized with model.

Availability

• Available in Mac OS X v10.4 and later.

Declared In

NSPersistentStoreCoordinator.h

lock

Attempts to acquire a lock.

- (void)lock

Discussion

This method blocks a thread’s execution until the lock can be acquired. An application protects a critical section of code by requiring a thread to acquire a lock before executing the code. Once the critical section is past, the thread relinquishes the lock by invoking unlock.

Availability

• Available in Mac OS X v10.4 and later.

See Also

• – tryLock
• – unlock

Declared In

NSPersistentStoreCoordinator.h

managedObjectIDForURIRepresentation:

Returns an object ID for the specified URI representation of an object ID if a matching store is available, or nil if a matching store cannot be found.

- (NSManagedObjectID *)managedObjectIDForURIRepresentation:(NSURL *)URL

Parameters

URL

An URL object containing a URI that specify a managed object.

Return Value

An object ID for the object specified by URL.

Discussion

The URI representation contains a UUID of the store the ID is coming from, and the coordinator can match it against the stores added to it.

Availability

• Available in Mac OS X v10.4 and later.

See Also

• URIRepresentation (NSManagedObjectID)
• objectWithID: (NSManagedObjectContext)

Declared In

NSPersistentStoreCoordinator.h

managedObjectModel

Returns the receiver’s managed object model.

- (NSManagedObjectModel *)managedObjectModel

Return Value

The receiver’s managed object model.

Availability

• Available in Mac OS X v10.4 and later.

Declared In

NSPersistentStoreCoordinator.h

metadataForPersistentStore:

Returns a dictionary that contains the metadata currently stored or to-be-stored in a given persistent store.

- (NSDictionary *)metadataForPersistentStore:(NSPersistentStore *)store

Parameters

store

A persistent store.

Return Value

A dictionary that contains the metadata currently stored or to-be-stored in store.

Availability

• Available in Mac OS X v10.4 and later.

See Also

• – setMetadata:forPersistentStore:
• + metadataForPersistentStoreOfType:URL:error:
• + setMetadata:forPersistentStoreOfType:URL:error:

Declared In

NSPersistentStoreCoordinator.h

migratePersistentStore:toURL:options:withType:error:

Moves a persistent store to a new location, changing the storage type if necessary.

- (NSPersistentStore *)migratePersistentStore:(NSPersistentStore *)store toURL:(NSURL *)URL options:(NSDictionary *)options withType:(NSString *)storeType error:(NSError **)error

Parameters

store

A persistent store.

URL

An URL object that specifies the location for the new store.

options

A dictionary containing key-value pairs that specify whether the store should be read-only, and whether (for an XML store) the XML file should be validated against the DTD before it is read. For key definitions, see “Store Options.”

storeType

A string constant (such as NSSQLiteStoreType) that specifies the type of the new store—see “Store Types.”

error

If an error occurs, upon return contains an instance of NSError that describes the problem.

Return Value

If the migration is successful, the new store, otherwise nil.

Discussion

This method is typically used for “Save As…” operations. Performance may vary depending on the type of old and new store. For more details of the action of this method, see Persistent Stores.

Availability

• Available in Mac OS X v10.4 and later.

See Also

• – addPersistentStoreWithType:configuration:URL:options:error:
• – removePersistentStore:error:

Declared In

NSPersistentStoreCoordinator.h

persistentStoreForURL:

Returns the persistent store for the specified URL.

- (NSPersistentStore *)persistentStoreForURL:(NSURL *)URL

Parameters

URL

An URL object that specifies the location of a persistent store.

Return Value

The persistent store at the location specified by URL.

Availability

• Available in Mac OS X v10.4 and later.

See Also

• – persistentStores
• – URLForPersistentStore:

Declared In

NSPersistentStoreCoordinator.h

persistentStores

Returns an array of persistent stores associated with the receiver.

- (NSArray *)persistentStores

Return Value

An array persistent stores associated with the receiver.

Availability

• Available in Mac OS X v10.4 and later.

See Also

• – persistentStoreForURL:
• – URLForPersistentStore:

Declared In

NSPersistentStoreCoordinator.h

removePersistentStore:error:

Removes a given persistent store.

- (BOOL)removePersistentStore:(NSPersistentStore *)store error:(NSError **)error

Parameters

store

A persistent store.

error

If an error occurs, upon return contains an instance of NSError that describes the problem.

Return Value

YES if the store is removed, otherwise NO.

Availability

• Available in Mac OS X v10.4 and later.

See Also

• – addPersistentStoreWithType:configuration:URL:options:error:
• – migratePersistentStore:toURL:options:withType:error:

Declared In

NSPersistentStoreCoordinator.h

setMetadata:forPersistentStore:

Sets the metadata stored in the persistent store during the next save operation executed on it to metadata.

- (void)setMetadata:(NSDictionary *)metadata forPersistentStore:(NSPersistentStore *)store

Parameters

metadata

A dictionary containing metadata for the store.

store

A persistent store.

Discussion

The store type and UUID (NSStoreTypeKey and NSStoreUUIDKey) are always added automatically, however NSStoreUUIDKey is only added if it is not set manually as part of the dictionary argument.

Availability

• Available in Mac OS X v10.4 and later.

See Also

• – metadataForPersistentStore:
• + setMetadata:forPersistentStoreOfType:URL:error:
• + metadataForPersistentStoreOfType:URL:error:

Declared In

NSPersistentStoreCoordinator.h

setURL:forPersistentStore:

Sets the URL for a given persistent store.

- (BOOL)setURL:(NSURL *)url forPersistentStore:(NSPersistentStore *)store

Parameters

url

The new location for store.

store

A persistent store associated with the receiver.

Return Value

YES if the store was relocated, otherwise NO.

Discussion

For atomic stores, this method alters the location to which the next save operation will write the file; for non-atomic stores, invoking this method will release the existing connection and create a new one at the specified URL. (For non-atomic stores, a store must already exist at the destination URL; a new store will not be created.)

Availability

• Available in Mac OS X v10.5 and later.

Declared In

NSPersistentStoreCoordinator.h

tryLock

Attempts to acquire a lock.

- (BOOL)tryLock

Return Value

YES if successful, otherwise NO.

Discussion

Returns immediately—contrast lock which blocks.

Availability

• Available in Mac OS X v10.4 and later.

See Also

• – lock
• – unlock

Declared In

NSPersistentStoreCoordinator.h

unlock

Relinquishes a previously acquired lock.

- (void)unlock

Availability

• Available in Mac OS X v10.4 and later.

See Also

• – lock
• – tryLock

Declared In

NSPersistentStoreCoordinator.h

URLForPersistentStore:

Returns the URL for a given persistent store.

- (NSURL *)URLForPersistentStore:(NSPersistentStore *)store

Parameters

store

A persistent store.

Return Value

The URL for store.

Availability

• Available in Mac OS X v10.4 and later.

See Also

• – persistentStoreForURL:
• – persistentStores

Declared In

NSPersistentStoreCoordinator.h

Constants

Store Types

Types of persistent store.

NSString * const NSSQLiteStoreType;
NSString * const NSXMLStoreType;
NSString * const NSBinaryStoreType;
NSString * const NSInMemoryStoreType;

Constants

NSSQLiteStoreType

The SQLite database store type.

Available in Mac OS X v10.4 and later.

Declared in NSPersistentStoreCoordinator.h

NSXMLStoreType

The XML store type.

Available in Mac OS X v10.4 and later.

Declared in NSPersistentStoreCoordinator.h

NSBinaryStoreType

The binary store type.

Available in Mac OS X v10.4 and later.

Declared in NSPersistentStoreCoordinator.h

NSInMemoryStoreType

The in-memory store type.

Available in Mac OS X v10.4 and later.

Declared in NSPersistentStoreCoordinator.h

Declared In

NSPersistentStoreCoordinator.h

Store Metadata

Keys used in a store’s metadata dictionary.

NSString * const NSStoreTypeKey;
NSString * const NSStoreUUIDKey;

Constants

NSStoreTypeKey

The key in the metadata dictionary to identify the store type.

Available in Mac OS X v10.4 and later.

Declared in NSPersistentStoreCoordinator.h

NSStoreUUIDKey

The key in the metadata dictionary to identify the store UUID.

The store UUID is useful to identify stores through URI representations, but it is not guaranteed to be unique. The UUID generated for new stores is unique—users can freely copy files and thus the UUID stored inside—so if you track or reference stores explicitly you need to be aware of duplicate UUIDs and potentially override the UUID when a new store is added to the list of known stores in your application.

Available in Mac OS X v10.4 and later.

Declared in NSPersistentStoreCoordinator.h

Declared In

NSPersistentStoreCoordinator.h

Stores Change Notification User Info Keys

An NSPersistentStoreCoordinatorStoresDidChangeNotification notification is posted whenever persistent stores are added to or removed from a persistent store coordinator, or when store UUIDs change. The userInfo dictionary contains information about the stores that were added or removed using these keys.

NSString * const NSAddedPersistentStoresKey;
NSString * const NSRemovedPersistentStoresKey;
NSString * const NSUUIDChangedPersistentStoresKey;

Constants

NSAddedPersistentStoresKey

Key for the array of stores that were added.

Available in Mac OS X v10.4 and later.

Declared in NSPersistentStoreCoordinator.h

NSRemovedPersistentStoresKey

Key for the array of stores that were removed.

Available in Mac OS X v10.4 and later.

Declared in NSPersistentStoreCoordinator.h

NSUUIDChangedPersistentStoresKey

Key for the array of stores whose UUIDs changed.

Available in Mac OS X v10.4 and later.

Declared in NSPersistentStoreCoordinator.h

Declared In

NSPersistentStoreCoordinator.h

Store Options

Keys for the options dictionary used in addPersistentStoreWithType:configuration:URL:options:error: and migratePersistentStore:toURL:options:withType:error:.

NSString * const NSReadOnlyPersistentStoreOption;
NSString * const NSValidateXMLStoreOption;
NSString * const NSPersistentStoreTimeoutOption;
NSString * const NSSQLitePragmasOption;

Constants

NSReadOnlyPersistentStoreOption

A flag that indicates whether a store is treated as read-only or not.

The default value is NO.

Available in Mac OS X v10.4 and later.

Declared in NSPersistentStoreCoordinator.h

NSValidateXMLStoreOption

A flag that indicates whether an XML file should be validated with the DTD while opening.

The default value is NO.

Available in Mac OS X v10.4 and later.

Declared in NSPersistentStoreCoordinator.h

NSPersistentStoreTimeoutOption

Options key that specifies the connection timeout for Core Data stores.

The corresponding value is an NSNumber object that represents the duration in seconds that Core Data will wait while attempting to create a connection to a persistent store. If a connection is cannot be made within that timeframe, the operation is aborted and an error is returned.

Available in Mac OS X v10.5 and later.

Declared in NSPersistentStoreCoordinator.h

NSSQLitePragmasOption

Options key for a dictionary of SQLite pragma settings with pragma values indexed by pragma names as keys.

All pragma values must be specified as NSString objects. The fullfsync and synchronous pragmas control the tradeoff between write performance (write to disk speed & cache utilization) and durability (data loss/corruption sensitivity to power interruption). For more information on pragma settings, see http://sqlite.org/pragma.html.

Available in Mac OS X v10.5 and later.

Declared in NSPersistentStoreCoordinator.h

Declared In

NSPersistentStoreCoordinator.h

Migration Options

Migration options, specified in the dictionary of options when adding a persistent store using addPersistentStoreWithType:configuration:URL:options:error:.

NSString * const NSIgnorePersistentStoreVersioningOption;
NSString * const NSMigratePersistentStoresAutomaticallyOption;

Constants

NSIgnorePersistentStoreVersioningOption

Key to ignore the built-in versioning provided by Core Data.

The corresponding value is an NSNumber object. If the boolValue of the number is YES, Core Data will not compare the version hashes between the managed object model in the coordinator and the metadata for the loaded store. (It will, however, continue to update the version hash information in the metadata.) This key and corresponding value of YES is specified by default for all applications linked on or before Mac OS X 10.4.

Available in Mac OS X v10.5 and later.

Declared in NSPersistentStoreCoordinator.h

NSMigratePersistentStoresAutomaticallyOption

Key to automatically attempt to migrate versioned stores.

The corresponding value is an NSNumber object. If the boolValue of the number is YES and if the version hash information for the added store is determined to be incompatible with the model for the coordinator, Core Data will attempt to locate the source and mapping models in the application bundles, and perform a migration.

Available in Mac OS X v10.5 and later.

Declared in NSPersistentStoreCoordinator.h

Declared In

NSPersistentStoreCoordinator.h

Versioning Support

Keys in store metadata to support versioning.

NSString * const NSStoreModelVersionHashesKey;
NSString * const NSStoreModelVersionIdentifiersKey;
NSString * const NSPersistentStoreOSCompatibility;

Constants

NSStoreModelVersionHashesKey

Key to represent the version hash information for the model used to create the store.

This key is used in the metadata for a persistent store.

Available in Mac OS X v10.5 and later.

Declared in NSPersistentStoreCoordinator.h

NSStoreModelVersionIdentifiersKey

Key to represent the version identifier for the model used to create the store.

This key is used in the metadata for a persistent store.

Available in Mac OS X v10.5 and later.

Declared in NSPersistentStoreCoordinator.h

NSPersistentStoreOSCompatibility

Key to represent the earliest version of Mac OS X the persistent store supports.

The corresponding value is an NSNumber object that takes the form of the constants defined by the Mac OS X availability macros (defined in /usr/include/AvailabilityMacros.h), for example 1040 represents Mac OS X version 10.4.0.

Backward compatibility may preclude some features.

Available in Mac OS X v10.5 and later.

Declared in NSPersistentStoreCoordinator.h

Declared In

NSPersistentStoreCoordinator.h

Notifications

NSPersistentStoreCoordinatorStoresDidChangeNotification

Posted whenever persistent stores are added to or removed from a persistent store coordinator, or when store UUIDs change.

The notification's object is the persistent store coordinator that was affected. The notification's userInfo dictionary contains information about the stores that were added or removed, specified using the following keys:

Availability

• Available in Mac OS X v10.4 and later.

Declared In

NSPersistentStoreCoordinator.h

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