包含组件

最底层File System -> SQLite -> NSPersistent Store（可有多个） -> NSPersistent StoreCoordinator -> NSManagedObjectContext（可有多个，每个可包含多个NSManagedObject）

设置堆栈

范例：https://github.com/objcio/issue-4-full-core-data-application

- (void)setupManagedObjectContext
{
     //使用initWithConcurrencyType:来明确使用的是基于队列的并发模型
     self.managedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
     self.managedObjectContext.persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:self.managedObjectModel];
     NSError* error;
     [self.managedObjectContext.persistentStoreCoordinator
          addPersistentStoreWithType:NSSQLiteStoreType
          configuration:nil
          URL:self.storeURL
          options:nil
          error:&error];
     if (error) {
          NSLog(@"error: %@", error);
     }
     self.managedObjectContext.undoManager = [[NSUndoManager alloc] init];
}

创建模型

在xcode新建的Core Data选项中选择Data Model template，模型文件会被编译成.momd文件。模型创建完毕就可以创建与之对应的NSManagedObject子类。从菜单选择Editor > NSManagedObject subclass。

模型的属性

• 默认/可选：建议不使用带默认值的可选属性
• Transient：方便撤销操作和故障处理，建议使用transient属性
• 索引：提高读取速度
• 标量类型：默认NSNumber，也可以使用int64_t，float_t或BOOL。

创建Store类

存储类除了managed object context还有rootItem方法，程序启动时会查找这root item然后传给root view controller。

- (Item*)rootItem
{
     NSFetchRequest* request = [NSFetchRequest fetchRequestWithEntityName:@"Item"];
     request.predicate = [NSPredicate predicateWithFormat:@"parent = %@", nil];
     NSArray* objects = [self.managedObjectContext executeFetchRequest:request error:NULL];
     Item* rootItem = [objects lastObject];
     if (rootItem == nil) {
          rootItem = [Item insertItemWithTitle:nil
               parent:nil
               inManagedObjectContext:self.managedObjectContext];
     }
     return rootItem;
}

//增加一个item
+ (instancetype)insertItemWithTitle:(NSString*)title
     parent:(Item*)parent
     inManagedObjectContext:(NSManagedObjectContext *)managedObjectContext
{
     NSUInteger order = parent.numberOfChildren;
     Item* item = [NSEntityDescription insertNewObjectForEntityForName:self.entityName
          inManagedObjectContext:managedObjectContext];
     item.title = title;
     item.parent = parent;
     item.order = @(order);
     return item;
}

//获得子节点数量
- (NSUInteger)numberOfChildren
{
     return self.children.count;
}

//创建一个fetched results controller的方法方便自动更新table view
- (NSFetchedResultsController*)childrenFetchedResultsController
{
     NSFetchRequest* request = [NSFetchRequest fetchRequestWithEntityName:[self.class entityName]];
     request.predicate = [NSPredicate predicateWithFormat:@"parent = %@", self];
     request.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:@"order" ascending:YES]];
     return [[NSFetchedResultsController alloc] initWithFetchRequest:request
          managedObjectContext:self.managedObjectContext
          sectionNameKeyPath:nil
          cacheName:nil];
}

和Table View无缝结合

创建一个NSFetchedResultsController作为table view的data source

- (id)initWithTableView:(UITableView*)tableView
{
     self = [super init];
     if (self) {
          self.tableView = tableView;
          self.tableView.dataSource = self;
     }
     return self;
}

- (void)setFetchedResultsController:(NSFetchedResultsController*)fetchedResultsController
{
     _fetchedResultsController = fetchedResultsController;
     fetchedResultsController.delegate = self;
     [fetchedResultsController performFetch:NULL];
}

- (NSInteger)numberOfSectionsInTableView:(UITableView*)tableView
{
     return self.fetchedResultsController.sections.count;
}

- (NSInteger)tableView:(UITableView*)tableView numberOfRowsInSection:(NSInteger)sectionIndex
{
     id<NSFetchedResultsSectionInfo> section = self.fetchedResultsController.sections[sectionIndex];
     return section.numberOfObjects;
}

- (UITableViewCell*)tableView:(UITableView*)tableView
cellForRowAtIndexPath:(NSIndexPath*)indexPath
{
     id object = [self.fetchedResultsController objectAtIndexPath:indexPath];
     id cell = [tableView dequeueReusableCellWithIdentifier:self.reuseIdentifier
          forIndexPath:indexPath];
     [self.delegate configureCell:cell withObject:object];
     return cell;
}

创建Table View Controller

在新建的Table view的viewDidLoad里写：

fetchedResultsControllerDataSource = [[FetchedResultsControllerDataSource alloc] initWithTableView:self.tableView];
self.fetchedResultsControllerDataSource.fetchedResultsController = self.parent.childrenFetchedResultsController;
fetchedResultsControllerDataSource.delegate = self;
fetchedResultsControllerDataSource.reuseIdentifier = @"Cell";

实现delegate

- (void)configureCell:(id)theCell withObject:(id)object
{
     UITableViewCell* cell = theCell;
     Item* item = object;
     cell.textLabel.text = item.title;
}

添加

在textFieldShouldReturn：里

[Item insertItemWithTitle:title
          parent:self.parent
          inManagedObjectContext:self.parent.managedObjectContext];
     textField.text = @"";
     [textField resignFirstResponder];

增删改后table view也会更改显示

- (void)controller:(NSFetchedResultsController*)controller
     didChangeObject:(id)anObject
     atIndexPath:(NSIndexPath*)indexPath
     forChangeType:(NSFetchedResultsChangeType)type
     newIndexPath:(NSIndexPath*)newIndexPath
{
     if (type == NSFetchedResultsChangeInsert) {
          [self.tableView insertRowsAtIndexPaths:@[newIndexPath]
               withRowAnimation:UITableViewRowAnimationAutomatic];
     }
}

- (void)controllerWillChangeContent:(NSFetchedResultsController*)controller
{
     [self.tableView beginUpdates];
}

- (void)controllerDidChangeContent:(NSFetchedResultsController*)controller
{
     [self.tableView endUpdates];
}

和Collection View的结合

范例：https://github.com/AshFurrow/UICollectionView-NSFetchedResultsController collection view没有beginUpdates和endUpdates方法，所以只能用performBatchUpdate方法收集所有更新，然后在controllerDidChangeContent中用block执行所有更新。

如何传递Table view里的Model对象到新的view controller中

- (void)prepareForSegue:(UIStoryboardSegue*)segue sender:(id)sender
{
     [super prepareForSegue:segue sender:sender];
     if ([segue.identifier isEqualToString:selectItemSegue]) {
          [self presentSubItemViewController:segue.destinationViewController];
     }
}

- (void)presentSubItemViewController:(ItemViewController*)subItemViewController
{
     Item* item = [self.fetchedResultsControllerDataSource selectedItem];
     subItemViewController.parent = item;
}

- (void)viewWillAppear:(BOOL)animated
{
     [super viewWillAppear:animated];
     self.fetchedResultsControllerDataSource.paused = NO;
}

- (void)viewWillDisappear:(BOOL)animated
{
     [super viewWillDisappear:animated];
     self.fetchedResultsControllerDataSource.paused = YES;
}

- (void)setPaused:(BOOL)paused
{
     _paused = paused;
     if (paused) {
          self.fetchedResultsController.delegate = nil;
     } else {
          self.fetchedResultsController.delegate = self;
          [self.fetchedResultsController performFetch:NULL];
          [self.tableView reloadData];
     }
}

删除

//让table view支持滑动删除
- (BOOL)tableView:(UITableView*)tableView
canEditRowAtIndexPath:(NSIndexPath*)indexPath
{
     return YES;
}

- (void)tableView:(UITableView *)tableView
     commitEditingStyle:(UITableViewCellEditingStyle)editingStyle
     forRowAtIndexPath:(NSIndexPath *)indexPath {
     if (editingStyle == UITableViewCellEditingStyleDelete) {
          id object = [self.fetchedResultsController objectAtIndexPath:indexPath];
          [self.delegate deleteObject:object];
     }
}

//强制order变化，可以重写prepareForDeletion方法
- (void)prepareForDeletion
{
     NSSet* siblings = self.parent.children;
     NSPredicate* predicate = [NSPredicate predicateWithFormat:@"order > %@", self.order];
     NSSet* siblingsAfterSelf = [siblings filteredSetUsingPredicate:predicate];
     [siblingsAfterSelf enumerateObjectsUsingBlock:^(Item* sibling, BOOL* stop)
     {
          sibling.order = @(sibling.order.integerValue - 1);
     }];
}

增加删除的动画效果

...
else if (type == NSFetchedResultsChangeDelete) {
     [self.tableView deleteRowsAtIndexPaths:@[indexPath]
          withRowAnimation:UITableViewRowAnimationAutomatic];
}

增加晃动撤销功能

//第一步告诉application支持这个
application.applicationSupportsShakeToEdit = YES;
//重写UIResponder类中的两个方法
- (BOOL)canBecomeFirstResponder {
     return YES;
}

- (NSUndoManager*)undoManager
{
     return self.managedObjectContext.undoManager;
}

//在持续化stack中设置一个undo manager
self.managedObjectContext.undoManager = [[NSUndoManager alloc] init];

//实现上面几步后晃动时会得到两个按钮的提醒框，可以给让用户体验更加友好些
NSString* title = textField.text;
NSString* actionName = [NSString stringWithFormat:NSLocalizedString(@"add item \"%@\"", @"Undo action name of add item"), title];
[self.undoManager setActionName:actionName];
[self.store addItem:title parent:nil];

排序

可以参考官方文档：https://developer.apple.com/library/ios/documentation/CoreData/Reference/NSFetchedResultsControllerDelegate_Protocol/Reference/Reference.html#//apple_ref/doc/uid/TP40008228-CH1-SW14

保存

• 保存是在managed object context中调用save。可以在applicationWillTerminate:中执行，也可能在applicationDIdEnterBackground:中。
• 异步存储Core Data 网络应用实例：（中文）http://objccn.io/issue-10-5/ （英文）http://www.objc.io/issue-10/networked-core-data-application.html

Fetch获取对象

基础

官方文档：https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/CoreData/Articles/cdFetching.html

范例

request.result = [NSPredicate predicateWithFormat:
     @"(%@ <= longitude) AND (longitude <= %@)"
     @"AND (%@ <= latitude) AND (latitude <= %@)",
     @(minLongitude), @(maxLongitude), @(minLatitude), @(maxLatitude)];
//取消将值放到row cache中。
request.returnsObjectsAsFaults = NO;
request.fetchLimit = 200;
//执行fetch
NSError *error = nil;
NSArray *stops = [moc executeFetchRequest:request error:&error];
NSAssert(stops != nil, @"Failed to execute %@: %@", request, error);
//二次遍历
NSPredicate *exactPredicate = [self exactLatitudeAndLongitudePredicateForCoordinate:self.location.coordinate];
stops = [stops filteredArrayUsingPredicate:exactPredicate];

- (NSPredicate *)exactLatitudeAndLongitudePredicateForCoordinate:(CLLocationCoordinate2D)pointOfInterest;
{
     return [NSPredicate predicateWithBlock:^BOOL(Stop *evaluatedStop, NSDictionary *bindings) {
          CLLocation *evaluatedLocation = [[CLLocation alloc] initWithLatitude:evaluatedStop.latitude           longitude:evaluatedStop.longitude];
          CLLocationDistance distance = [self.location distanceFromLocation:evaluatedLocation];
          return (distance < self.distance);
     }];
}

//子查询
NSPredicate *timePredicate = [NSPredicate predicateWithFormat:@"(%@ <= departureTime) && (departureTime <= %@)”, startDate, endDate];

NSPredicate *predicate = [NSPredicate predicateWithFormat:
     @"(SUBQUERY(stopTimes, $x, (%@ <= $x.departureTime) && ($x.departureTime <= %@)).@count != 0)”, startDate, endDate];

//文本搜索
NSString *searchString = @"U Görli";
predicate = [NSPredicate predicateWithFormat:@"name BEGINSWITH %@", searchString];

导入大量数据

导入应用Bundle里的SQLite文件

NSFileManager* fileManager = [NSFileManager defaultManager];
NSError *error;

if([fileManager fileExistsAtPath:self.storeURL.path]) {
     NSURL *storeDirectory = [self.storeURL URLByDeletingLastPathComponent];
     NSDirectoryEnumerator *enumerator = [fileManager enumeratorAtURL:storeDirectory
          includingPropertiesForKeys:nil
          options:0
          errorHandler:NULL];
     NSString *storeName = [self.storeURL.lastPathComponent stringByDeletingPathExtension];
     //遍历目录下是否有重复
     for (NSURL *url in enumerator) {
          if (![url.lastPathComponent hasPrefix:storeName]) continue;
          [fileManager removeItemAtURL:url error:&error];
     }
      // 处理错误
}

NSString* bundleDbPath = [[NSBundle mainBundle] pathForResource:@"seed" ofType:@"sqlite"];
[fileManager copyItemAtPath:bundleDbPath toPath:self.storeURL.path error:&error];

//真机删除会失效，所以使用版本号来进行区分新旧
NSString* bundleVersion = [infoDictionary objectForKey:(NSString *)kCFBundleVersionKey];
NSString *seedVersion = [[NSUserDefaults standardUserDefaults] objectForKey@"SeedVersion"];
if (![seedVersion isEqualToString:bundleVersion]) {
     // 复制源数据库
}

// ... 导入成功后
NSDictionary *infoDictionary = [NSBundle mainBundle].infoDictionary;
[[NSUserDefaults standardUserDefaults] setObject:bundleVersion forKey:@"SeedVersion"];

导入范例

https://github.com/objcio/issue-4-importing-and-fetching

版本迁移

Mapping Models

NSMigrationManager能够推断两个版本模型的映射关系，但是如果版本跨度大了就力不从心了。

Progressive Migrations渐进式迁移

实现原理是两个版本之间确保正常，升级时按照一个版本一个版本渐进式的升级方式，比如最新的版本是第四版，如果用户使用的是第二版的，那么升级是就是先从第二版升级到第三版，然后再从第三版升级到第四版。完整范例：https://github.com/objcio/issue-4-core-data-migration 主要代码来自Marcus Zarrahttps://twitter.com/mzarra ，他的书关于Core Data的值得一看，http://pragprog.com/book/mzcd2/core-data

迁移策略

NSEntityMigrationPolicy这个类不光能够修改Entity的属性和关系，还能够自定义一些操作完成每个Entity的迁移。例如在Entity Mapping的Custom Polity里写上自定义的polity的方法

NSNumber *modelVersion = [mapping.userInfo valueForKey:@"modelVersion"];
if (modelVersion.integerValue == 2) {
     NSMutableArray *sourceKeys = [sourceInstance.entity.attributesByName.allKeys mutableCopy];
     NSDictionary *sourceValues = [sourceInstance dictionaryWithValuesForKeys:sourceKeys];
     NSManagedObject *destinationInstance = [NSEntityDescription insertNewObjectForEntityForName:mapping.destinationEntityName
          inManagedObjectContext:manager.destinationContext];
     NSArray *destinationKeys = destinationInstance.entity.attributesByName.allKeys;
     for (NSString *key in destinationKeys) {
          id value = [sourceValues valueForKey:key];
          // 避免value为空
          if (value && ![value isEqual:[NSNull null]]) {
               [destinationInstance setValue:value forKey:key];
          }
     }
}

NSMutableDictionary *authorLookup = [manager lookupWithKey:@"authors"];
// 检查该作者是否已经被创建了
NSString *authorName = [sourceInstance valueForKey:@"author"];
NSManagedObject *author = [authorLookup valueForKey:authorName];
if (!author) {
     // 创建作者
     // ...

     // 更新避免重复
     [authorLookup setValue:author forKey:authorName];
}
[destinationInstance performSelector:@selector(addAuthorsObject:) withObject:author];

//源存储和目的存储之间的关系
[manager associateSourceInstance:sourceInstance
     withDestinationInstance:destinationInstance
     forEntityMapping:mapping];
return YES;

NSmigrationManager的category方法

@implementation NSMigrationManager (Lookup)

- (NSMutableDictionary *)lookupWithKey:(NSString *)lookupKey
{
     NSMutableDictionary *userInfo = (NSMutableDictionary *)self.userInfo;
     // 这里检查一下是否已经建立了 userInfo 的字典
     if (!userInfo) {
          userInfo = [@{} mutableCopy];
          self.userInfo = userInfo;
     }
     NSMutableDictionary *lookup = [userInfo valueForKey:lookupKey];
     if (!lookup) {
          lookup = [@{} mutableCopy];
          [userInfo setValue:lookup forKey:lookupKey];
     }
     return lookup;
}

@end

更复杂的迁移

NSArray *users = [sourceInstance valueForKey:@"users"];
for (NSManagedObject *user in users) {

     NSManagedObject *file = [NSEntityDescription insertNewObjectForEntityForName:@"File"
          inManagedObjectContext:manager.destinationContext];
     [file setValue:[sourceInstance valueForKey:@"fileURL"] forKey:@"fileURL"];
     [file setValue:destinationInstance forKey:@"book"];

     NSInteger userId = [[user valueForKey:@"userId"] integerValue];
     NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"User"];
     request.predicate = [NSPredicate predicateWithFormat:@"userId = %d", userId];
     NSManagedObject *user = [[manager.destinationContext executeFetchRequest:request error:nil] lastObject];
     [file setValue:user forKey:@"user"];
}

数据量大时的迁移改造，利用CoreData提供的chunks数据块方式。官方文档https://developer.apple.com/library/ios/documentation/cocoa/Conceptual/CoreDataVersioning/Articles/vmCustomizing.html#//apple_ref/doc/uid/TP40004399-CH8-SW9

NSArray *mappingModels = @[mappingModel]; // 我们之前建立的那个模型
if ([self.delegate respondsToSelector:@selector(migrationManager:mappingModelsForSourceModel:)]) {
     NSArray *explicitMappingModels = [self.delegate migrationManager:self
          mappingModelsForSourceModel:sourceModel];
     if (0 < explicitMappingModels.count) {
          mappingModels = explicitMappingModels;
     }
}
for (NSMappingModel *mappingModel in mappingModels) {
     didMigrate = [manager migrateStoreFromURL:sourceStoreURL
          type:type
          options:nil
          withMappingModel:mappingModel
          toDestinationURL:destinationStoreURL
          destinationType:type
          destinationOptions:nil
          error:error];
}

- (NSArray *)migrationManager:(MHWMigrationManager *)migrationManager
     mappingModelsForSourceModel:(NSManagedObjectModel *)sourceModel
{
     NSMutableArray *mappingModels = [@[] mutableCopy];
     NSString *modelName = [sourceModel mhw_modelName];
     if ([modelName isEqual:@"Model2"]) {
          // 把该映射模型加入数组
     }
     return mappingModels;
}

- (NSString *)mhw_modelName
{
     NSString *modelName = nil;
     NSArray *modelPaths = // get paths to all the mom files in the bundle
     for (NSString *modelPath in modelPaths) {
          NSURL *modelURL = [NSURL fileURLWithPath:modelPath];
          NSManagedObjectModel *model = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
          if ([model isEqual:self]) {
               modelName = modelURL.lastPathComponent.stringByDeletingPathExtension;
               break;
          }
     }
     return modelName;
}

建立单元测试，

- (void)setUpCoreDataStackMigratingFromStoreWithName:(NSString *)name
{
     NSURL *storeURL = [self temporaryRandomURL];
     [self copyStoreWithName:name toURL:storeURL];

     NSURL *momURL = [[NSBundle mainBundle] URLForResource:@"Model" withExtension:@"momd"];
     self.managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:momURL];

     NSString *storeType = NSSQLiteStoreType;

     MHWMigrationManager *migrationManager = [MHWMigrationManager new];
     [migrationManager progressivelyMigrateURL:storeURL
          ofType:storeType
          toModel:self.managedObjectModel
          error:nil];

     self.persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:self.managedObjectModel];
     [self.persistentStoreCoordinator addPersistentStoreWithType:storeType
          configuration:nil
          URL:storeURL
          options:nil
          error:nil];

     self.managedObjectContext = [[NSManagedObjectContext alloc] init];
     self.managedObjectContext.persistentStoreCoordinator = self.persistentStoreCoordinator;
}

- (NSURL *)temporaryRandomURL
{
     NSString *uniqueName = [NSProcessInfo processInfo].globallyUniqueString;
     return [NSURL fileURLWithPath:[NSTemporaryDirectory() stringByAppendingString:uniqueName]];
}

- (void)copyStoreWithName:(NSString *)name toURL:(NSURL *)url
{
     // 每次创建一个唯一的url以保证测试正常运行
     NSBundle *bundle = [NSBundle bundleForClass:[self class]];
     NSFileManager *fileManager = [NSFileManager new];
     NSString *path = [bundle pathForResource:[name stringByDeletingPathExtension] ofType:name.pathExtension];
     [fileManager copyItemAtPath:path
          toPath:url.path error:nil];
}

//在测试类中复用
- (void)setUp
{
     [super setUp];
     [self setUpCoreDataStackMigratingFromStoreWithName:@"Model1.sqlite"];
}

调试迁移一个有用的启动参数是-com.apple.CoreData.MigrationDebug，设置1就会在console收到迁移数据时会出现的特殊的情况的信息。如果设置-com.apple.CoreData.SQLDebug 为 1还能够在console看到实际操作的SQL语句。

Core Data的并行处理

• 官方文档有基本规则：https://developer.apple.com/library/mac/#documentation/cocoa/conceptual/CoreData/Articles/cdConcurrency.html
• 处理步骤，先创建一个操作，创建一个managed object context，和main managed object context使用同样的persistent store coordinator，当context保存后就通知main managed object context，后再合并变化。可以参考这个范例https://github.com/objcio/issue-2-background-core-data

性能测试

• 加上-com.apple.CoreData.SQLDebug1 作为启动参数传递给应用程序可以得到的输出

sql: SELECT 0, t0.Z_PK, t0.Z_OPT, t0.ZIDENTIFIER, t0.ZLATITUDE, t0.ZLONGITUDE, t0.ZNAME FROM ZSTOP t0 WHERE (? <= t0.ZLONGITUDE AND t0.ZLONGITUDE <= ? AND ? <= t0.ZLATITUDE AND t0.ZLATITUDE <= ?) LIMIT 100
annotation: sql connection fetch time: 0.0008s
annotation: total fetch execution time: 0.0013s for 15 rows.

实际生成的SQL是：

SELECT 0, t0.Z_PK, t0.Z_OPT, t0.ZIDENTIFIER, t0.ZLATITUDE, t0.ZLONGITUDE, t0.ZNAME FROM ZSTOP t0
WHERE (? <= t0.ZLONGITUDE AND t0.ZLONGITUDE <= ? AND ? <= t0.ZLATITUDE AND t0.ZLATITUDE <= ?)
LIMIT 200

• 使用SQL 的EXPLAIN命令https://www.sqlite.org/eqp.html对性能调查研究

% cd TrafficSearch
% sqlite3 transit-data.sqlite
SQLite version 3.7.13 2012-07-17 17:46:21
Enter ".help" for instructions
Enter SQL statements terminated with a ";"
sqlite> EXPLAIN QUERY PLAN SELECT 0, t0.Z_PK, t0.Z_OPT, t0.ZIDENTIFIER, t0.ZLATITUDE, t0.ZLONGITUDE, t0.ZNAME FROM ZSTOP t0
...> WHERE (13.30845219672199 <= t0.ZLONGITUDE AND t0.ZLONGITUDE <= 13.33441458422844 AND 52.42769566863058 <= t0.ZLATITUDE AND t0.ZLATITUDE <= 52.44352370653525)
...> LIMIT 100;
0|0|0|SEARCH TABLE ZSTOP AS t0 USING INDEX ZSTOP_ZLONGITUDE_INDEX (ZLONGITUDE>? AND ZLONGITUDE<?) (~6944 rows)

输出

0|0|0|SEARCH TABLE ZSTOP AS t0 USING INDEX ZSTOP_ZLONGITUDE_ZLATITUDE (ZLONGITUDE>? AND ZLONGITUDE<?) (~6944 rows)