RKEntityByAttributeCache Class Reference
| Inherits from | NSObject |
| Declared in | RKEntityByAttributeCache.h |
Overview
The RKEntityByAttributeCache class provides an in-memory caching mechanism for managed objects instances of an entity in a managed object context with the value of one of the object’s attributes acting as the cache key. When loaded, the cache will retrieve all instances of an entity from the store and build a dictionary mapping values for the given cache key attribute to the managed object ID for all objects matching the value. The cache can then be used to quickly retrieve objects by attribute value for the cache key without executing another fetch request against the managed object context. This can provide a large performance improvement when a large number of objects are being retrieved using a particular attribute as the key.
RKEntityByAttributeCache instances are used by the RKEntityCache to provide caching for multiple entities at once.
Bug: Please note that the RKEntityByAttribute cache is implemented using a NSFetchRequest with a result type of NSDictionaryResultType. This means that the cache cannot load pending object instances via a fetch from the load method. Pending objects must be manually added to the cache via addObject: if it is desirable for the pending objects to be retrieved by subsequent invocations of objectWithAttributeValue:inContext: and objectsWithAttributeValue:inContext: prior to a save.
This is a limitation imposed by Core Data. The dictionary result type implementation is leveraged instead a normal fetch request because it offers very large performance and memory utilization improvements by avoiding construction of managed object instances and faulting.
Tasks
Creating a Cache
-
– initWithEntity:attributes:managedObjectContext:Initializes the receiver with a given entity, attribute, and managed object context.
Getting Cache Identity
-
entityThe Core Data entity description for the managed objects being cached.
property -
attributesAn array of attribute names specifying attributes of the cached entity that act as the cache key.
property -
managedObjectContextThe managed object context the receiver fetches cached objects from.
property -
monitorsContextForChangesA Boolean value determining if the receiever monitors the managed object context for changes and updates the cache entries using the notifications emitted.
property
Loading and Flushing the Cache
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– loadLoads the cache by finding all instances of the configured entity and building an association between the value of the cached attribute’s value and the managed object ID for the object.
-
– flushFlushes the cache by releasing all cache attribute value to managed object ID associations.
Inspecting Cache State
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– isLoadedA Boolean value indicating if the cache has loaded associations between cache attribute values and managed object ID’s.
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– countReturns a count of the total number of cached objects.
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– countWithAttributeValues:Returns the total number of cached objects whose attributes match the values in the given dictionary of attribute values.
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– countOfAttributeValuesReturns the number of unique attribute values contained within the receiver.
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– containsObject:Returns a Boolean value that indicates whether a given object is present in the cache.
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– containsObjectWithAttributeValues:Returns a Boolean value that indicates whether one of more objects is present in the cache with a given value of the cache key attribute.
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– objectWithAttributeValues:inContext:Returns the first object with a matching value for the cache key attributes in a given managed object context.
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– objectsWithAttributeValues:inContext:Returns the collection of objects with a matching value for the cache key attribute in a given managed object context.
Managing Cached Objects
-
– addObject:Adds a managed object to the cache.
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– removeObject:Removes a managed object from the cache.
Properties
attributes
An array of attribute names specifying attributes of the cached entity that act as the cache key.
@property (nonatomic, readonly) NSArray *attributesDeclared In
RKEntityByAttributeCache.hentity
The Core Data entity description for the managed objects being cached.
@property (nonatomic, readonly) NSEntityDescription *entityDeclared In
RKEntityByAttributeCache.hInstance Methods
addObject:
Adds a managed object to the cache.
- (void)addObject:(NSManagedObject *)objectParameters
- object
The managed object to add to the cache.
Discussion
The object must be an instance of the cached entity.
Declared In
RKEntityByAttributeCache.hcontainsObject:
Returns a Boolean value that indicates whether a given object is present in the cache.
- (BOOL)containsObject:(NSManagedObject *)objectParameters
- object
An object.
Return Value
YES if object is present in the cache, otherwise NO.
Declared In
RKEntityByAttributeCache.hcontainsObjectWithAttributeValues:
Returns a Boolean value that indicates whether one of more objects is present in the cache with a given value of the cache key attribute.
- (BOOL)containsObjectWithAttributeValues:(NSDictionary *)attributeValuesParameters
- attributeValue
The value with which to check the cache for objects with a matching value.
Return Value
YES if one or more objects with the given value for the cache key attribute is present in the cache, otherwise NO.
Declared In
RKEntityByAttributeCache.hcount
Returns a count of the total number of cached objects.
- (NSUInteger)countDeclared In
RKEntityByAttributeCache.hcountOfAttributeValues
Returns the number of unique attribute values contained within the receiver.
- (NSUInteger)countOfAttributeValuesReturn Value
The number of unique attribute values within the receiver.
Declared In
RKEntityByAttributeCache.hcountWithAttributeValues:
Returns the total number of cached objects whose attributes match the values in the given dictionary of attribute values.
- (NSUInteger)countWithAttributeValues:(NSDictionary *)attributeValuesParameters
- attributeValues
The value for the cache key attribute to retrieve a count of the objects with a matching value.
Return Value
The number of objects in the cache with the given value for the cache attribute of the receiver.
Declared In
RKEntityByAttributeCache.hflush
Flushes the cache by releasing all cache attribute value to managed object ID associations.
- (void)flushDeclared In
RKEntityByAttributeCache.hinitWithEntity:attributes:managedObjectContext:
Initializes the receiver with a given entity, attribute, and managed object context.
- (id)initWithEntity:(NSEntityDescription *)entity attributes:(NSArray *)attributeNames managedObjectContext:(NSManagedObjectContext *)contextParameters
- entity
The Core Data entity description for the managed objects being cached.
- attributeNames
An array of attribute names used as the cache keys.
- context
The managed object context the cache retrieves the cached objects from.
Return Value
The receiver, initialized with the given entity, attribute, and managed object
context.
Declared In
RKEntityByAttributeCache.hisLoaded
A Boolean value indicating if the cache has loaded associations between cache attribute values and managed object ID’s.
- (BOOL)isLoadedDeclared In
RKEntityByAttributeCache.hload
Loads the cache by finding all instances of the configured entity and building an association between the value of the cached attribute’s value and the managed object ID for the object.
- (void)loadDeclared In
RKEntityByAttributeCache.hobjectWithAttributeValues:inContext:
Returns the first object with a matching value for the cache key attributes in a given managed object context.
- (NSManagedObject *)objectWithAttributeValues:(NSDictionary *)attributeValues inContext:(NSManagedObjectContext *)contextParameters
- attributeValues
A value for the cache key attribute.
- context
The managed object context to retrieve the object from.
Return Value
An object with the value of attribute matching attributeValue or nil.
Declared In
RKEntityByAttributeCache.hobjectsWithAttributeValues:inContext:
Returns the collection of objects with a matching value for the cache key attribute in a given managed object context.
- (NSSet *)objectsWithAttributeValues:(NSDictionary *)attributeValues inContext:(NSManagedObjectContext *)contextParameters
- context
The managed object context to retrieve the objects from.
- attributeValue
A value for the cache key attribute.
Return Value
An array of objects with the value of attribute matching attributeValue or an empty array.
Declared In
RKEntityByAttributeCache.hremoveObject:
Removes a managed object from the cache.
- (void)removeObject:(NSManagedObject *)objectParameters
- object
The managed object to remove from the cache.
Discussion
The object must be an instance of the cached entity.
Declared In
RKEntityByAttributeCache.h