前面详
细讲解了 Core Data 的框架以及设计的类，下面我们来讲解一个完全手动编写代码使用这些类的示例，这个例子来自苹果官方示例。在这个例子里面，我们打算做这样一件事 情：记录程序运行记录（时间与 process id），并保存到xml文件中。我们使用 Core Data 来做这个事情。
二，创建并设置模型类
示例代码下载：点击这里
一， 建立一个新的 Mac command-line tool application 工程，命名为 CoreDataTutorial。为支持垃圾主动回收机制，点击项目名称，在右边的 Build Setting 中查找 garbage 关键字，将找到的 Objective-C Garbage Collection 设置为 Required [-fobj-gc-only]。并将 main.m 中 的 main() 方法修改为如下：
int main ( int argc, const char * argv[])
{
NSLog( @" === Core Data Tutorial === " );
// Enable GC
//
objc_startCollectorThread();
return 0 ;
}
{
NSLog( @" === Core Data Tutorial === " );
// Enable GC
//
objc_startCollectorThread();
return 0 ;
}
二，创建并设置模型类
在 main() 之前添加如下方法：
NSManagedObjectModel * managedObjectModel()
{
static NSManagedObjectModel * moModel = nil;
if (moModel != nil) {
return moModel;
}
moModel = [[NSManagedObjectModel alloc] init];
// Create the entity
//
NSEntityDescription * runEntity = [[NSEntityDescription alloc] init];
[runEntity setName: @" Run " ];
[runEntity setManagedObjectClassName: @" Run " ];
[moModel setEntities:[NSArray arrayWithObject:runEntity]];
// Add the Attributes
//
NSAttributeDescription * dateAttribute = [[NSAttributeDescription alloc] init];
[dateAttribute setName: @" date " ];
[dateAttribute setAttributeType:NSDateAttributeType];
[dateAttribute setOptional:NO];
NSAttributeDescription * idAttribute = [[NSAttributeDescription alloc] init];
[idAttribute setName: @" processID " ];
[idAttribute setAttributeType:NSInteger32AttributeType];
[idAttribute setOptional:NO];
[idAttribute setDefaultValue:[NSNumber numberWithInteger: - 1 ]];
// Create the validation predicate for the process ID.
// The following code is equivalent to validationPredicate = [NSPredicate predicateWithFormat:@"SELF > 0"]
//
NSExpression * lhs = [NSExpression expressionForEvaluatedObject];
NSExpression * rhs = [NSExpression expressionForConstantValue:[NSNumber numberWithInteger: 0 ]];
NSPredicate * validationPredicate = [NSComparisonPredicate
predicateWithLeftExpression:lhs
rightExpression:rhs
modifier:NSDirectPredicateModifier
type:NSGreaterThanPredicateOperatorType
options: 0 ];
NSString * validationWarning = @" Process ID < 1 " ;
[idAttribute setValidationPredicates:[NSArray arrayWithObject:validationPredicate]
withValidationWarnings:[NSArray arrayWithObject:validationWarning]];
// set the properties for the entity.
//
NSArray * properties = [NSArray arrayWithObjects: dateAttribute, idAttribute, nil];
[runEntity setProperties:properties];
// Add a Localization Dictionary
//
NSMutableDictionary * localizationDictionary = [NSMutableDictionary dictionary];
[localizationDictionary setObject: @" Date " forKey: @" Property/date/Entity/Run " ];
[localizationDictionary setObject: @" Process ID " forKey: @" Property/processID/Entity/Run " ];
[localizationDictionary setObject: @" Process ID must not be less than 1 " forKey: @" ErrorString/Process ID < 1 " ];
[moModel setLocalizationDictionary:localizationDictionary];
return moModel;
}
{
static NSManagedObjectModel * moModel = nil;
if (moModel != nil) {
return moModel;
}
moModel = [[NSManagedObjectModel alloc] init];
// Create the entity
//
NSEntityDescription * runEntity = [[NSEntityDescription alloc] init];
[runEntity setName: @" Run " ];
[runEntity setManagedObjectClassName: @" Run " ];
[moModel setEntities:[NSArray arrayWithObject:runEntity]];
// Add the Attributes
//
NSAttributeDescription * dateAttribute = [[NSAttributeDescription alloc] init];
[dateAttribute setName: @" date " ];
[dateAttribute setAttributeType:NSDateAttributeType];
[dateAttribute setOptional:NO];
NSAttributeDescription * idAttribute = [[NSAttributeDescription alloc] init];
[idAttribute setName: @" processID " ];
[idAttribute setAttributeType:NSInteger32AttributeType];
[idAttribute setOptional:NO];
[idAttribute setDefaultValue:[NSNumber numberWithInteger: - 1 ]];
// Create the validation predicate for the process ID.
// The following code is equivalent to validationPredicate = [NSPredicate predicateWithFormat:@"SELF > 0"]
//
NSExpression * lhs = [NSExpression expressionForEvaluatedObject];
NSExpression * rhs = [NSExpression expressionForConstantValue:[NSNumber numberWithInteger: 0 ]];
NSPredicate * validationPredicate = [NSComparisonPredicate
predicateWithLeftExpression:lhs
rightExpression:rhs
modifier:NSDirectPredicateModifier
type:NSGreaterThanPredicateOperatorType
options: 0 ];
NSString * validationWarning = @" Process ID < 1 " ;
[idAttribute setValidationPredicates:[NSArray arrayWithObject:validationPredicate]
withValidationWarnings:[NSArray arrayWithObject:validationWarning]];
// set the properties for the entity.
//
NSArray * properties = [NSArray arrayWithObjects: dateAttribute, idAttribute, nil];
[runEntity setProperties:properties];
// Add a Localization Dictionary
//
NSMutableDictionary * localizationDictionary = [NSMutableDictionary dictionary];
[localizationDictionary setObject: @" Date " forKey: @" Property/date/Entity/Run " ];
[localizationDictionary setObject: @" Process ID " forKey: @" Property/processID/Entity/Run " ];
[localizationDictionary setObject: @" Process ID must not be less than 1 " forKey: @" ErrorString/Process ID < 1 " ];
[moModel setLocalizationDictionary:localizationDictionary];
return moModel;
}
在上面的代码中：
1）我们创建了一个全局模型 moModel；
2）并在其中创建一个名为 Run 的 Entity，这个 Entity 对应的 ManagedObject 类名为 Run（很快我们将创建这样一个类）；
3）给 Run Entity 添加了两个必须的 Property：date 和 processID，分别表示运行时间以及进程 ID；并设置默认的进程 ID 为 -1；
4）给 processID 特性设置检验条件：必须大于 0；
5）给模型设置本地化描述词典；
本地化描述提供对 Entity，Property，Error信息等的便于理解的描述，其可用的键值对如下表：
|
Key |
Value |
|
|
"Entity/NonLocalizedEntityName" |
"LocalizedEntityName" |
|
|
"Property/NonLocalizedPropertyName/Entity/EntityName" |
"LocalizedPropertyName" |
|
|
"Property/NonLocalizedPropertyName" |
"LocalizedPropertyName" |
|
|
"ErrorString/NonLocalizedErrorString" |
"LocalizedErrorString" |
|
三，创建并设置运行时类和对象
由于要用到存储功能，所以我们必须定义持久化数据的存储路径，在 main() 之前添加如下方法设置存储路径：
NSURL * applicationLogDirectory()
{
NSString * LOG_DIRECTORY = @" CoreDataTutorial " ;
static NSURL * ald = nil;
if (ald == nil)
{
NSFileManager * fileManager = [[NSFileManager alloc] init];
NSError * error = nil;
NSURL * libraryURL = [fileManager URLForDirectory:NSLibraryDirectory inDomain:NSUserDomainMask
appropriateForURL:nil create:YES error: & error];
if (libraryURL == nil) {
NSLog( @" Could not access Library directory\n%@ " , [error localizedDescription]);
}
else
{
ald = [libraryURL URLByAppendingPathComponent: @" Logs " ];
ald = [ald URLByAppendingPathComponent:LOG_DIRECTORY];
NSLog( @" >> log path %@ " , [ald path]);
NSDictionary * properties = [ald resourceValuesForKeys:[NSArray arrayWithObject:NSURLIsDirectoryKey] error: & error];
if (properties == nil)
{
if ( ! [fileManager createDirectoryAtPath:[ald path] withIntermediateDirectories:YES attributes:nil error: & error])
{
NSLog( @" Could not create directory %@\n%@ " ,
[ald path], [error localizedDescription]);
ald = nil;
}
}
}
}
return ald;
}
{
NSString * LOG_DIRECTORY = @" CoreDataTutorial " ;
static NSURL * ald = nil;
if (ald == nil)
{
NSFileManager * fileManager = [[NSFileManager alloc] init];
NSError * error = nil;
NSURL * libraryURL = [fileManager URLForDirectory:NSLibraryDirectory inDomain:NSUserDomainMask
appropriateForURL:nil create:YES error: & error];
if (libraryURL == nil) {
NSLog( @" Could not access Library directory\n%@ " , [error localizedDescription]);
}
else
{
ald = [libraryURL URLByAppendingPathComponent: @" Logs " ];
ald = [ald URLByAppendingPathComponent:LOG_DIRECTORY];
NSLog( @" >> log path %@ " , [ald path]);
NSDictionary * properties = [ald resourceValuesForKeys:[NSArray arrayWithObject:NSURLIsDirectoryKey] error: & error];
if (properties == nil)
{
if ( ! [fileManager createDirectoryAtPath:[ald path] withIntermediateDirectories:YES attributes:nil error: & error])
{
NSLog( @" Could not create directory %@\n%@ " ,
[ald path], [error localizedDescription]);
ald = nil;
}
}
}
}
return ald;
}
下面，我们来创建运行时对象：ManagedObjectContext 和 PersistentStoreCoordinator。
NSManagedObjectContext * managedObjectContext()
{
static NSManagedObjectContext * moContext = nil;
if (moContext != nil) {
return moContext;
}
moContext = [[NSManagedObjectContext alloc] init];
// Create a persistent store coordinator, then set the coordinator for the context.
//
NSManagedObjectModel * moModel = managedObjectModel();
NSPersistentStoreCoordinator * coordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:moModel];
[moContext setPersistentStoreCoordinator: coordinator];
// Create a new persistent store of the appropriate type.
//
NSString * STORE_TYPE = NSXMLStoreType;
NSString * STORE_FILENAME = @" CoreDataTutorial.xml " ;
NSError * error = nil;
NSURL * url = [applicationLogDirectory() URLByAppendingPathComponent:STORE_FILENAME];
NSPersistentStore * newStore = [coordinator addPersistentStoreWithType:STORE_TYPE
configuration:nil
URL:url
options:nil
error: & error];
if (newStore == nil) {
NSLog( @" Store Configuration Failure\n%@ " , ([error localizedDescription] != nil) ? [error localizedDescription] : @" Unknown Error " );
}
return moContext;
}
在上面的代码中： {
static NSManagedObjectContext * moContext = nil;
if (moContext != nil) {
return moContext;
}
moContext = [[NSManagedObjectContext alloc] init];
// Create a persistent store coordinator, then set the coordinator for the context.
//
NSManagedObjectModel * moModel = managedObjectModel();
NSPersistentStoreCoordinator * coordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:moModel];
[moContext setPersistentStoreCoordinator: coordinator];
// Create a new persistent store of the appropriate type.
//
NSString * STORE_TYPE = NSXMLStoreType;
NSString * STORE_FILENAME = @" CoreDataTutorial.xml " ;
NSError * error = nil;
NSURL * url = [applicationLogDirectory() URLByAppendingPathComponent:STORE_FILENAME];
NSPersistentStore * newStore = [coordinator addPersistentStoreWithType:STORE_TYPE
configuration:nil
URL:url
options:nil
error: & error];
if (newStore == nil) {
NSLog( @" Store Configuration Failure\n%@ " , ([error localizedDescription] != nil) ? [error localizedDescription] : @" Unknown Error " );
}
return moContext;
}
1）我们创建了一个全局 ManagedObjectContext 对象 moContext；
2）并在设置其 persistent store coordinator，存储类型为 xml，保存文件名为：CoreDataTutorial.xml，并将其放到前面定义的存储路径下。
好，至此万事具备，只欠 ManagedObject 了！下面我们就来定义这个数据对象类。向工程添加 Core Data->NSManagedObject subclass 的类，名为 Run (模型中 Entity 定义的类名) 。
Run.h
//
// Run.h
// CoreDataTutorial
//
// Created by kesalin on 8/29/11.
// Copyright 2011 kesalin@gmail.com. All rights reserved.
//
#import < CoreData / NSManagedObject.h >
@interface Run : NSManagedObject
{
NSInteger processID;
}
@property (retain) NSDate * date;
@property (retain) NSDate * primitiveDate;
@property NSInteger processID;
@end
// Run.h
// CoreDataTutorial
//
// Created by kesalin on 8/29/11.
// Copyright 2011 kesalin@gmail.com. All rights reserved.
//
#import < CoreData / NSManagedObject.h >
@interface Run : NSManagedObject
{
NSInteger processID;
}
@property (retain) NSDate * date;
@property (retain) NSDate * primitiveDate;
@property NSInteger processID;
@end
Run.m
//
// Run.m
// CoreDataTutorial
//
// Created by kesalin on 8/29/11.
// Copyright 2011 kesalin@gmail.com. All rights reserved.
//
#import " Run.h "
@implementation Run
@dynamic date;
@dynamic primitiveDate;
- ( void ) awakeFromInsert
{
[super awakeFromInsert];
self.primitiveDate = [NSDate date];
}
#pragma mark -
#pragma mark Getter and setter
- (NSInteger)processID
{
[self willAccessValueForKey: @" processID " ];
NSInteger pid = processID;
[self didAccessValueForKey: @" processID " ];
return pid;
}
- ( void )setProcessID:(NSInteger)newProcessID
{
[self willChangeValueForKey: @" processID " ];
processID = newProcessID;
[self didChangeValueForKey: @" processID " ];
}
// Implement a setNilValueForKey: method. If the key is “processID” then set processID to 0.
//
- ( void )setNilValueForKey:(NSString * )key {
if ([key isEqualToString: @" processID " ]) {
self.processID = 0 ;
}
else {
[super setNilValueForKey:key];
}
}
@end
// Run.m
// CoreDataTutorial
//
// Created by kesalin on 8/29/11.
// Copyright 2011 kesalin@gmail.com. All rights reserved.
//
#import " Run.h "
@implementation Run
@dynamic date;
@dynamic primitiveDate;
- ( void ) awakeFromInsert
{
[super awakeFromInsert];
self.primitiveDate = [NSDate date];
}
#pragma mark -
#pragma mark Getter and setter
- (NSInteger)processID
{
[self willAccessValueForKey: @" processID " ];
NSInteger pid = processID;
[self didAccessValueForKey: @" processID " ];
return pid;
}
- ( void )setProcessID:(NSInteger)newProcessID
{
[self willChangeValueForKey: @" processID " ];
processID = newProcessID;
[self didChangeValueForKey: @" processID " ];
}
// Implement a setNilValueForKey: method. If the key is “processID” then set processID to 0.
//
- ( void )setNilValueForKey:(NSString * )key {
if ([key isEqualToString: @" processID " ]) {
self.processID = 0 ;
}
else {
[super setNilValueForKey:key];
}
}
@end
注意：
1）这个类中的 date 和 primitiveDate 的访问属性为 @dynamic，这表明在运行期会动态生成对应的 setter 和 getter；
2） 在这里我们演示了如何正确地手动实现 processID 的 setter 和 getter：为了让 ManagedObjecContext 能够检测 processID的变化，以及自动支持 undo/redo，我们需要在访问和更改数据对象时告之系统，will/didAccessValueForKey 以及 will/didChangeValueForKey 就是起这个作用的。
3）当我们设置 nil 给数据对象 processID 时，我们可以在 setNilValueForKey 捕获这个情况，并将 processID 置 0；
4）当数据对象被插入到 ManagedObjectContext 时，我们在 awakeFromInsert 将时间设置为当前时间。
三，创建或读取数据对象，设置其值，保存
好，至此真正的万事具备，我们可以创建或从持久化文件中读取数据对象，设置其值，并将其保存到持久化文件中。本例中持久化文件为 xml 文件。修改 main() 中代码如下：
int main ( int argc, const char * argv[])
{
NSLog( @" === Core Data Tutorial === " );
// Enable GC
//
objc_startCollectorThread();
NSError * error = nil;
NSManagedObjectModel * moModel = managedObjectModel();
NSLog( @" The managed object model is defined as follows:\n%@ " , moModel);
if (applicationLogDirectory() == nil) {
exit( 1 );
}
NSManagedObjectContext * moContext = managedObjectContext();
// Create an Instance of the Run Entity
//
NSEntityDescription * runEntity = [[moModel entitiesByName] objectForKey: @" Run " ];
Run * run = [[Run alloc] initWithEntity:runEntity insertIntoManagedObjectContext:moContext];
NSProcessInfo * processInfo = [NSProcessInfo processInfo];
run.processID = [processInfo processIdentifier];
if ( ! [moContext save: & error]) {
NSLog( @" Error while saving\n%@ " , ([error localizedDescription] != nil) ? [error localizedDescription] : @" Unknown Error " );
exit( 1 );
}
// Fetching Run Objects
//
NSFetchRequest * request = [[NSFetchRequest alloc] init];
[request setEntity:runEntity];
NSSortDescriptor * sortDescriptor = [[NSSortDescriptor alloc] initWithKey: @" date " ascending:YES];
[request setSortDescriptors:[NSArray arrayWithObject:sortDescriptor]];
error = nil;
NSArray * array = [moContext executeFetchRequest:request error: & error];
if ((error != nil) || (array == nil))
{
NSLog( @" Error while fetching\n%@ " , ([error localizedDescription] != nil) ? [error localizedDescription] : @" Unknown Error " );
exit( 1 );
}
// Display the Results
//
NSDateFormatter * formatter = [[NSDateFormatter alloc] init];
[formatter setDateStyle:NSDateFormatterMediumStyle];
[formatter setTimeStyle:NSDateFormatterMediumStyle];
NSLog( @" %@ run history: " , [processInfo processName]);
for (run in array)
{
NSLog( @" On %@ as process ID %ld " , [formatter stringForObjectValue:run.date], run.processID);
}
return 0 ;
}
{
NSLog( @" === Core Data Tutorial === " );
// Enable GC
//
objc_startCollectorThread();
NSError * error = nil;
NSManagedObjectModel * moModel = managedObjectModel();
NSLog( @" The managed object model is defined as follows:\n%@ " , moModel);
if (applicationLogDirectory() == nil) {
exit( 1 );
}
NSManagedObjectContext * moContext = managedObjectContext();
// Create an Instance of the Run Entity
//
NSEntityDescription * runEntity = [[moModel entitiesByName] objectForKey: @" Run " ];
Run * run = [[Run alloc] initWithEntity:runEntity insertIntoManagedObjectContext:moContext];
NSProcessInfo * processInfo = [NSProcessInfo processInfo];
run.processID = [processInfo processIdentifier];
if ( ! [moContext save: & error]) {
NSLog( @" Error while saving\n%@ " , ([error localizedDescription] != nil) ? [error localizedDescription] : @" Unknown Error " );
exit( 1 );
}
// Fetching Run Objects
//
NSFetchRequest * request = [[NSFetchRequest alloc] init];
[request setEntity:runEntity];
NSSortDescriptor * sortDescriptor = [[NSSortDescriptor alloc] initWithKey: @" date " ascending:YES];
[request setSortDescriptors:[NSArray arrayWithObject:sortDescriptor]];
error = nil;
NSArray * array = [moContext executeFetchRequest:request error: & error];
if ((error != nil) || (array == nil))
{
NSLog( @" Error while fetching\n%@ " , ([error localizedDescription] != nil) ? [error localizedDescription] : @" Unknown Error " );
exit( 1 );
}
// Display the Results
//
NSDateFormatter * formatter = [[NSDateFormatter alloc] init];
[formatter setDateStyle:NSDateFormatterMediumStyle];
[formatter setTimeStyle:NSDateFormatterMediumStyle];
NSLog( @" %@ run history: " , [processInfo processName]);
for (run in array)
{
NSLog( @" On %@ as process ID %ld " , [formatter stringForObjectValue:run.date], run.processID);
}
return 0 ;
}
在上面的代码中：
1）我们先获得全局的 NSManagedObjectModel 和 NSManagedObjectContext 对象：moModel 和 moContext；
2）并创建一个Run Entity，设置其 Property processID 为当前进程的 ID；
3） 将该数据对象保存到持久化文件中：[moContext save: &error]。我们无需与 PersistentStoreCoordinator 打交道，只需要给 ManagedObjectContext 发送 save 消息即可，NSManagedObjectContext 会透明地在后面处理对持久化数据文件的读写；
4）然后我们创建一个 FetchRequest 来查询持久化数据文件中保存的数据记录，并将结果按照日期升序排列。查询操作也是由 ManagedObjectContext 来处理的： [moContextexecuteFetchRequest:request error:&error];
5）将查询结果打印输出；
最后，不要忘记导入相关头文件：
#import < Foundation / Foundation.h >
#import < CoreData / CoreData.h >
#include < objc / objc - auto.h >
#import " Run.h "
#import < CoreData / CoreData.h >
#include < objc / objc - auto.h >
#import " Run.h "
好！大功告成！编译运行，我们可以得到如下显示：
2011-09-03 21:42:47.556 CoreDataTutorial[992:903] CoreDataTutorial run history:
2011-09-03 21:42:47.557 CoreDataTutorial[992:903] On 2011-9-3 下午09:41:56 as process ID 940
2011-09-03 21:42:47.557 CoreDataTutorial[992:903] On 2011-9-3 下午09:42:16 as process ID 955
2011-09-03 21:42:47.558 CoreDataTutorial[992:903] On 2011-9-3 下午09:42:20 as process ID 965
2011-09-03 21:42:47.558 CoreDataTutorial[992:903] On 2011-9-3 下午09:42:24 as process ID 978
2011-09-03 21:42:47.559 CoreDataTutorial[992:903] On 2011-9-3 下午09:42:47 as process ID 992
2011-09-03 21:42:47.557 CoreDataTutorial[992:903] On 2011-9-3 下午09:41:56 as process ID 940
2011-09-03 21:42:47.557 CoreDataTutorial[992:903] On 2011-9-3 下午09:42:16 as process ID 955
2011-09-03 21:42:47.558 CoreDataTutorial[992:903] On 2011-9-3 下午09:42:20 as process ID 965
2011-09-03 21:42:47.558 CoreDataTutorial[992:903] On 2011-9-3 下午09:42:24 as process ID 978
2011-09-03 21:42:47.559 CoreDataTutorial[992:903] On 2011-9-3 下午09:42:47 as process ID 992
通 过这个例子，我们可以更好理解 Core Data 的运作机制。在 Core Data 中我们最常用的就是 ManagedObjectContext，它几乎参与对数据对象的所有操作，包括对 undo/redo 的支持；而 Entity 对应的运行时类为 ManagedObject，我们可以理解为抽象数据结构 Entity 在内存中由 ManagedObject 来体现，而 Perproty 数据类型在内存中则由 ManagedObject 类的成员属性来体现。一般我们不需要与 PersistentStoreCoordinator 打交道，对数据文件的读写操作都由 ManagedObjectContext 为我们代劳了。
作者：u010773008 发表于2013-7-24 13:09:14 原文链接
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