Inherits from | |
Conforms to | |
Framework | /System/Library/Frameworks/CoreData.framework |
Availability | Available in Mac OS X v10.4 and later. |
Declared in | NSManagedObjectModel.h |
Companion guides | |
Related sample code |
An NSManagedObjectModel
object describes a schema—a collection of entities (data models) that you use in your application.
The model contains one or more NSEntityDescription
objects representing the entities in the schema. Each NSEntityDescription
object has property description objects (instances of subclasses of NSPropertyDescription
) that represent the properties (or fields) of the entity in the schema. The Core Data framework uses this description in several ways:
Constraining UI creation in Interface Builder
Validating attribute and relationship values at runtime
Mapping between your managed objects and a database or file-based schema for object persistence.
A managed object model maintains a mapping between each of its entity objects and a corresponding managed object class for use with the persistent storage mechanisms in the Core Data Framework. You can determine the entity for a particular managed object with the entity
method.
You typically create managed object models using the data modeling tool in Xcode, but it is possible to build an model programmatically if needed.
Managed object model files are typically stored in a project or a framework. To load a model, you provide an URL to the constructor. Note that loading a model doesn’t have the effect of loading all of its entities.
It is often the case that in your application you want to get hold of a collection of objects that share features in common. Sometimes you can define those features (property values) in advance; sometimes you need to be able to supply values at runtime. For example, you might want to be able to retrieve all movies owned by Pixar; alternatively you might want to be able to retrieve all movies that earned more than an amount specified by the user at runtime.
Fetch requests are often predefined in a managed object model as templates. They allow you to pre-define named queries and their parameters in the model. Typically they contain variables that need to be substituted at runtime. NSManagedObjectModel
provides API to retrieve a stored fetch request by name, and to perform variable substitution—see fetchRequestTemplateForName:
and fetchRequestFromTemplateWithName:substitutionVariables:
. You can create fetch request templates programmatically, and associate them with a model using setFetchRequestTemplate:forName:
; typically, however, you define them using the Xcode design tool.
Sometimes a model—particularly one in a framework—may be used in different situations, and you may want to specify different sets of entities to be used in different situations. There might, for example, be certain entities that should only be available if a user has administrative privileges. To support this requirement, a model may have more than one configuration. Each configuration is named, and has an associated set of entities. The sets may overlap. You establish configurations programmatically using setEntities:forConfiguration:
or using the Xcode design tool, and retrieve the entities for a given configuration name using entitiesForConfiguration:
.
Since a model describes the structure of the data in a persistent store, changing any parts of a model that alters the schema renders it incompatible with (and so unable to open) the stores it previously created. If you change your schema, you therefore need to migrate the data in existing stores to new version (see Versioning in Core Data Programming Guide). For example, if you add a new entity or a new attribute to an existing entity, you will not be able to open old stores; if you add a validation constraint or set a new default value for an attribute, you will be able to open old stores.
Managed object models are editable until they are used by an object graph manager (a managed object context or a persistent store coordinator). This allows you to create or modify them dynamically. However, once a model is being used, it must not be changed. This is enforced at runtime—when the object manager first fetches data using a model, the whole of that model becomes uneditable. Any attempt to mutate a model or any of its sub-objects after that point causes an exception to be thrown. If you need to modify a model that is in use, create a copy, modify the copy, and then discard the objects with the old model.
In Mac OS X v10.5 and later, NSManagedObjectModel
supports the NSFastEnumeration
protocol. You can use this to enumerate over a model’s entities, as illustrated in the following example:
NSManagedObjectModel *aModel = ...; |
for (NSEntityDescription *entity in aModel) { |
// entity is each instance of NSEntityDescription in aModel in turn |
} |
– initWithContentsOfURL:
+ mergedModelFromBundles:
+ mergedModelFromBundles:forStoreMetadata:
+ modelByMergingModels:
+ modelByMergingModels:forStoreMetadata:
– entities
– entitiesByName
– setEntities:
– configurations
– entitiesForConfiguration:
– setEntities:forConfiguration:
– fetchRequestTemplatesByName
– fetchRequestTemplateForName:
– fetchRequestFromTemplateWithName:substitutionVariables:
– setFetchRequestTemplate:forName:
– isConfiguration:compatibleWithStoreMetadata:
– entityVersionHashesByName
– versionIdentifiers
– setVersionIdentifiers:
Returns a model created by merging all the models found in given bundles.
+ (NSManagedObjectModel *)mergedModelFromBundles:(NSArray *)bundles
An array of instances of NSBundle
to search. If you specify nil
, then the main bundle is searched.
A model created by merging all the models found in bundles.
+ mergedModelFromBundles:forStoreMetadata:
+ modelByMergingModels:
+ modelByMergingModels:forStoreMetadata:
– initWithContentsOfURL:
NSManagedObjectModel.h
Returns a merged model from a specified array for the version information in provided metadata.
+ (NSManagedObjectModel *)mergedModelFromBundles:(NSArray *)bundles forStoreMetadata:(NSDictionary *)metadata
An array of bundles.
A dictionary containing version information from the metadata for a persistent store.
The managed object model used to create the store for the metadata. If a model cannot be created to match the version information specified by metadata, returns nil
.
This method is a companion to mergedModelFromBundles:
.
+ mergedModelFromBundles:
+ modelByMergingModels:
+ modelByMergingModels:forStoreMetadata:
– initWithContentsOfURL:
NSManagedObjectModel.h
Creates a single model from an array of existing models.
+ (NSManagedObjectModel *)modelByMergingModels:(NSArray *)models
An array of instances of NSManagedObjectModel
.
A single model made by combining the models in models.
You use this method to combine multiple models (typically from different frameworks) into one.
+ mergedModelFromBundles:
+ mergedModelFromBundles:forStoreMetadata:
+ modelByMergingModels:forStoreMetadata:
– initWithContentsOfURL:
NSManagedObjectModel.h
Returns, for the version information in given metadata, a model merged from a given array of models.
+ (NSManagedObjectModel *)modelByMergingModels:(NSArray *)models forStoreMetadata:(NSDictionary *)metadata
An array of instances of NSManagedObjectModel
.
A dictionary containing version information from the metadata for a persistent store.
A merged model from models for the version information in metadata. If a model cannot be created to match the version information in metadata, returns nil
.
This is the companion method to mergedModelFromBundles:forStoreMetadata:
.
+ mergedModelFromBundles:
+ mergedModelFromBundles:forStoreMetadata:
+ modelByMergingModels:
– initWithContentsOfURL:
NSManagedObjectModel.h
Returns all the available configuration names of the receiver.
- (NSArray *)configurations
An array containing the available configuration names of the receiver.
NSManagedObjectModel.h
Returns the entities in the receiver.
- (NSArray *)entities
An array containing the entities in the receiver.
Entities are instances of NSEntityDescription
.
NSManagedObjectModel.h
Returns the entities of the receiver in a dictionary.
- (NSDictionary *)entitiesByName
The entities of the receiver in a dictionary, where the keys in the dictionary are the names of the corresponding entities.
– entities
– entitiesForConfiguration:
– setEntities:
– setEntities:forConfiguration:
+ entityForName:inManagedObjectContext:
(NSEntityDescription
)NSManagedObjectModel.h
Returns the entities of the receiver for a specified configuration.
- (NSArray *)entitiesForConfiguration:(NSString *)configuration
The name of a configuration in the receiver.
An array containing the entities of the receiver for the configuration specified by configuration.
NSManagedObjectModel.h
Returns a dictionary of the version hashes for the entities in the receiver.
- (NSDictionary *)entityVersionHashesByName
A dictionary of the version hashes for the entities in the receiver, keyed by entity name.
The dictionary of version hash information is used by Core Data to determine schema compatibility.
NSManagedObjectModel.h
Returns a copy of the fetch request template with the variables substituted by values from the substitutions dictionary.
- (NSFetchRequest *)fetchRequestFromTemplateWithName:(NSString *)name substitutionVariables:(NSDictionary *)variables
A string containing the name of a fetch request template.
A dictionary containing key-value pairs where the keys are the names of variables specified in the template; the corresponding values are substituted before the fetch request is returned. The dictionary must provide values for all the variables in the template.
A copy of the fetch request template with the variables substituted by values from variables.
The variables dictionary must provide values for all the variables. If you want to test for a nil value, use [NSNull null]
.
This method provides the usual way to bind an “abstractly” defined fetch request template to a concrete fetch. For more details on using this method, see Creating Predicates.
NSManagedObjectModel.h
Returns the fetch request with a specified name.
- (NSFetchRequest *)fetchRequestTemplateForName:(NSString *)name
A string containing the name of a fetch request template.
The fetch request named name.
If the template contains substitution variables, you should instead use fetchRequestFromTemplateWithName:substitutionVariables:
to create a new fetch request.
– fetchRequestTemplatesByName
– fetchRequestFromTemplateWithName:substitutionVariables:
– setFetchRequestTemplate:forName:
NSManagedObjectModel.h
Returns a dictionary of the receiver’s fetch request templates.
- (NSDictionary *)fetchRequestTemplatesByName
A dictionary of the receiver’s fetch request templates, keyed by name.
If the template contains a predicate with substitution variables, you should instead use fetchRequestFromTemplateWithName:substitutionVariables:
to create a new fetch request.
NSManagedObjectModel.h
Initializes the receiver using the model file at the specified URL.
- (id)initWithContentsOfURL:(NSURL *)url
An URL object specifying the location of a model file.
A managed object model initialized using the file at url.
+ mergedModelFromBundles:
+ mergedModelFromBundles:forStoreMetadata:
+ modelByMergingModels:
+ modelByMergingModels:forStoreMetadata:
NSManagedObjectModel.h
Returns a Boolean value that indicates whether a given configuration in the receiver is compatible with given metadata from a persistent store.
- (BOOL)isConfiguration:(NSString *)configuration compatibleWithStoreMetadata:(NSDictionary *)metadata
The name of a configuration in the receiver. Pass nil
to specify no configuration.
Metadata for a persistent store.
YES
if the configuration in the receiver specified by configuration is compatible with the store metadata given by metadata, otherwise NO
.
This method compares the version information in the store metadata with the entity versions of a given configuration. For information on specific differences, use entityVersionHashesByName
and perform an entity-by-entity comparison.
NSManagedObjectModel.h
Returns the localization dictionary of the receiver.
- (NSDictionary *)localizationDictionary
The localization dictionary of the receiver.
The key-value pattern is described in setLocalizationDictionary:
.
Note that in the implementation in Mac OS X v10.4, localizationDictionary
may return nil
until Core Data lazily loads the dictionary for its own purposes (for example, reporting a localized error).
NSManagedObjectModel.h
Sets the entities array of the receiver.
- (void)setEntities:(NSArray *)entities
An array of instances of NSEntityDescription
.
This method raises an exception if the receiver has been used by an object graph manager.
NSManagedObjectModel.h
Associates the specified entities with the receiver using the given configuration name.
- (void)setEntities:(NSArray *)entities forConfiguration:(NSString *)configuration
An array of instances of NSEntityDescription
.
A name for the configuration.
This method raises an exception if the receiver has been used by an object graph manager.
NSManagedObjectModel.h
Associates the specified fetch request with the receiver using the given name.
- (void)setFetchRequestTemplate:(NSFetchRequest *)fetchRequest forName:(NSString *)name
A fetch request, typically containing predicates with variables for substitution.
A string that specifies the name of the fetch request template.
For more details on using this method, see Creating Predicates.
This method raises an exception if the receiver has been used by an object graph manager.
– fetchRequestTemplatesByName
– fetchRequestTemplateForName:
– fetchRequestFromTemplateWithName:substitutionVariables:
NSManagedObjectModel.h
Sets the localization dictionary of the receiver.
- (void)setLocalizationDictionary:(NSDictionary *)localizationDictionary
A dictionary containing localized string values for entities, properties, and error strings related to the model. The key and value pattern is described in Table 1.
Table 1 describes the key and value pattern for the localization dictionary.
Key |
Value |
Note |
---|---|---|
"Entity/NonLocalizedEntityName" |
"LocalizedEntityName" |
|
"Property/NonLocalizedPropertyName/Entity/EntityName" |
"LocalizedPropertyName" |
(1) |
"Property/NonLocalizedPropertyName" |
"LocalizedPropertyName" |
|
"ErrorString/NonLocalizedErrorString" |
"LocalizedErrorString" |
(1) For properties in different entities with the same non-localized name but which should have different localized names.
NSManagedObjectModel.h
Sets the identifiers for the receiver.
- (void)setVersionIdentifiers:(NSSet *)identifiers
An array of identifiers for the receiver.
NSManagedObjectModel.h
Returns the collection of developer-defined version identifiers for the receiver.
- (NSSet *)versionIdentifiers
The collection of developer-defined version identifiers for the receiver. Merged models return the combined collection of identifiers.
The Core Data framework does not give models a default identifier, nor does it depend this value at runtime. For models created in Xcode, you set this value in the model inspector.
This value is meant to be used as a debugging hint to help you determine the models that were combined to create a merged model.
NSManagedObjectModel.h
© 2007 Apple Inc. All Rights Reserved. (Last updated: 2007-01-26)