在多線程環境中使用CoreData

在多線程環境中使用CoreData

BY 子非魚 · 2014 年 10 月 13 日

 

上回書說道，其實CoreData學起來也沒有很複雜，咱們其實增刪改查都和別的ORM大同小異。可是世界老是很複雜的，一根筋的去考慮問題很容易卡到蛋，默認狀況下咱們的代碼都在Main Thread中執行，數據庫操做一旦量多了，頻繁了，勢必會阻塞住主線程的其餘操做，俗話說，卡住了。

這個世界自然是多線程的，因此咱們操做數據也必須多線程。CoreData對多線程的支持比較奇怪（按照通常的思路來講），CoreData的NSPersistentStoreCoordinator和NSManagedObjectContext對象都是不能跨線程使用的，NSManagedObject也不行，有人想加鎖不就完了。No，做爲一個處女座是不能忍受這麼醜陋的解決方案的。其實NSManagedObjectContext已經對跨線程提供了內置的支持，只不過方式比較特殊，須要腦洞大開才行。

在建立NSManagedObject的時候有個構造器參數initWithConcurrencyType就是解決的關鍵所在，這個參數是一個枚舉，有三個可選值：

NSConfinementConcurrencyType (或者不加參數，默認就是這個)
NSMainQueueConcurrencyType (表示只會在主線程中執行)
NSPrivateQueueConcurrencyType (表示能夠在子線程中執行)
那麼究竟應該怎麼使用才能無阻塞無痛呢？

通過參考： http://www.cocoanetics.com/2012/07/multi-context-coredata/ 這篇文章，咱們使用三層 NSManagedObjectContext 嵌套的方式。

NSManagedObjectContext是能夠基於其餘的 NSManagedObjectContext的，經過 setParentContext 方法，能夠設置另一個 NSManagedObjectContext 爲本身的父級，這個時候子級能夠訪問父級下全部的對象，並且子級 NSManagedObjectContext 的內容變化後，若是執行save方法，會自動的 merge 到父級 NSManagedObjectContext 中，也就是子級save後，變更會同步到父級 NSManagedObjectContext。固然這個時候父級也必須再save一次，若是父級沒有父級了，那麼就會直接向NSPersistentStoreCoordinator中寫入，若是有就會接着向再上一層的父級冒泡……

那麼這裏如同參考的文章同樣，經過三個級別的 NSManagedObjectContext， 一個負責在background更新NSPersistentStoreCoordinator。一個用在主線程，主要執行插入，修改和刪除操做，一些小的查詢也能夠在這裏同步執行，若是有大的查詢，就起一個新的 NSPrivateQueueConcurrencyType 類型的 NSManagedObjectContext，而後放在後臺去執行查詢，查詢完成後將結果返回主線程。

NSManagedObjectContext在後臺線程執行是經過 performBlock 方法來實現的，在傳入的匿名block中執行的代碼就是在子線程中了，好比

[_bgObjectContext performBlock:^{

__block NSError *inner_error = nil;

[_bgObjectContext save:&inner_error];

}];

那麼若是是查詢的話，由於 NSManagedObject 也不能跨線程訪問，因此在block裏獲取到的NSManagedObject對象只能將objectid傳到主線程，主線程再經過 objectWithID 恢復對象的方法，以下面的示例：

+(void)one:(NSString*)predicate on:(ObjectResult)handler{

NSManagedObjectContext *ctx = [[mmDAO instance] createPrivateObjectContext];

[ctx performBlock:^{

NSFetchRequest *fetchRequest = [self makeRequest:ctx predicate:predicate orderby:nil offset:0 limit:1];

NSError* error = nil;

NSArray* results = [ctx executeFetchRequest:fetchRequest error:&error];

if (error) {

NSLog(@"error: %@", error);

[[mmDAO instance].mainObjectContext performBlock:^{

handler(@[], nil);

}];

}

if ([results count]<1) {

[[mmDAO instance].mainObjectContext performBlock:^{

handler(@[], nil);

}];

}

NSManagedObjectID *objId = ((NSManagedObject*)results[0]).objectID;

[[mmDAO instance].mainObjectContext performBlock:^{

handler([[mmDAO instance].mainObjectContext objectWithID:objId], nil);

}];

}];

}

最後咱們將上述的要點結合起來，解決方案就呼之欲出了。

首先咱們仍是須要一個抽象存儲和數據操做的核心

mmDAO.h

//

// mmDAO.h

// agent

//

// Created by LiMing on 14-6-24.

// Copyright (c) 2014年 Alexander. All rights reserved.

//

#import <Foundation/Foundation.h>

typedef void(^OperationResult)(NSError* error);

@interface mmDAO : NSObject

@property (readonly, strong, nonatomic) NSOperationQueue *queue;

@property (readonly ,strong, nonatomic) NSManagedObjectContext *bgObjectContext;

@property (readonly, strong, nonatomic) NSManagedObjectContext *mainObjectContext;

+(mmDAO*)instance;

-(void) setupEnvModel:(NSString *)model DbFile:(NSString*)filename;

- (NSManagedObjectContext *)createPrivateObjectContext;

-(NSError*)save:(OperationResult)handler;

@end

mmDAO.m

//

// mmDAO.m

// agent

//

// Created by LiMing on 14-6-24.

// Copyright (c) 2014年 Alexander. All rights reserved.

//

#import "mmDAO.h"

#import "mmAppDelegate.h"

static mmDAO *onlyInstance;

@interface mmDAO ()

@property (nonatomic, copy)NSString *modelName;

@property (nonatomic, copy)NSString *dbFileName;

@end

@implementation mmDAO

+(mmDAO*)instance{

static dispatch_once_t onceToken;

dispatch_once(&onceToken, ^{

onlyInstance = [[mmDAO alloc] init];

});

return onlyInstance;

}

- (instancetype)init

{

self = [super init];

if (self) {

}

return self;

}

-(void) setupEnvModel:(NSString *)model DbFile:(NSString*)filename{

_modelName = model;

_dbFileName = filename;

[self initCoreDataStack];

}

- (void)initCoreDataStack

{

NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];

if (coordinator != nil) {

_bgObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];

[_bgObjectContext setPersistentStoreCoordinator:coordinator];

_mainObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];

[_mainObjectContext setParentContext:_bgObjectContext];

}

}

- (NSManagedObjectContext *)createPrivateObjectContext

{

NSManagedObjectContext *ctx = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];

[ctx setParentContext:_mainObjectContext];

return ctx;

}

- (NSManagedObjectModel *)managedObjectModel

{

NSManagedObjectModel *managedObjectModel;

NSURL *modelURL = [[NSBundle mainBundle] URLForResource:_modelName withExtension:@"momd"];

managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];

return managedObjectModel;

}

- (NSPersistentStoreCoordinator *)persistentStoreCoordinator

{

NSPersistentStoreCoordinator *persistentStoreCoordinator = nil;

NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:_dbFileName];

NSError *error = nil;

persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];

if (![persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error]) {

NSLog(@"Unresolved error %@, %@", error, [error userInfo]);

abort();

}

return persistentStoreCoordinator;

}

- (NSURL *)applicationDocumentsDirectory

{

return [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];

}

-(NSError*)save:(OperationResult)handler{

NSError *error;

if ([_mainObjectContext hasChanges]) {

[_mainObjectContext save:&error];

[_bgObjectContext performBlock:^{

__block NSError *inner_error = nil;

[_bgObjectContext save:&inner_error];

if (handler){

//handler(error);

//這裏須要返回主線程，否則在回調裏操做界面會出錯

[_mainObjectContext performBlock:^{

handler(error);

}];

}

}];

}

return error;

}

@end

而後咱們擴展 NSManagedObject，把操做注入到類裏，這樣子有個好處是能夠自動獲取類名，而後就不用子級寫字符串的類名了。

NSManagedObject+helper.h

//

//  NSManagedObject+helper.h

//  agent

//

//  Created by LiMing on 14-6-24.

//  Copyright (c) 2014年 bangban. All rights reserved.

//

typedef void(^ListResult)(NSArray* result, NSError *error);

typedef void(^ObjectResult)(id result, NSError *error);

#import <CoreData/CoreData.h>

#import "mmDAO.h"

@interface NSManagedObject (helper)

+(id)createNew;

+(NSError*)save:(OperationResult)handler;

+(NSArray*)filter:(NSString *)predicate orderby:(NSArray *)orders offset:(int)offset limit:(int)limit;

+(void)filter:(NSString *)predicate orderby:(NSArray *)orders offset:(int)offset limit:(int)limit on:(ListResult)handler;

+(id)one:(NSString*)predicate;

+(void)one:(NSString*)predicate on:(ObjectResult)handler;

+(void)delobject:(id)object;

@end

NSManagedObject+helper.m

//

//  NSManagedObject+helper.m

//  agent

//

//  Created by LiMing on 14-6-24.

//  Copyright (c) 2014年 bangban. All rights reserved.

//

#import "NSManagedObject+helper.h"

@implementation NSManagedObject (helper)

+(id)createNew{

NSString *className = [NSString stringWithUTF8String:object_getClassName(self)];

return [NSEntityDescription insertNewObjectForEntityForName:className inManagedObjectContext:[mmDAO instance].mainObjectContext];

}

+(NSError*)save:(OperationResult)handler{

return [[mmDAO instance] save:handler];

}

+(NSArray*)filter:(NSString *)predicate orderby:(NSArray *)orders offset:(int)offset limit:(int)limit{

NSManagedObjectContext *ctx = [mmDAO instance].mainObjectContext;

NSFetchRequest *fetchRequest = [self makeRequest:ctx predicate:predicate orderby:orders offset:offset limit:limit];

NSError* error = nil;

NSArray* results = [ctx executeFetchRequest:fetchRequest error:&error];

if (error) {

NSLog(@"error: %@", error);

return @[];

}

return results;

}

+(NSFetchRequest*)makeRequest:(NSManagedObjectContext*)ctx predicate:(NSString*)predicate orderby:(NSArray*)orders offset:(int)offset limit:(int)limit{

NSString *className = [NSString stringWithUTF8String:object_getClassName(self)];

NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];

[fetchRequest setEntity:[NSEntityDescription entityForName:className inManagedObjectContext:ctx]];

[fetchRequest setPredicate:[NSPredicate predicateWithFormat:predicate]];

NSMutableArray *orderArray = [[NSMutableArray alloc] init];

if (orders!=nil) {

for (NSString *order in orders) {

NSSortDescriptor *orderDesc = nil;

if ([[order substringToIndex:1] isEqualToString:@"-"]) {

orderDesc = [[NSSortDescriptor alloc] initWithKey:[order substringFromIndex:1]

ascending:NO];

}else{

orderDesc = [[NSSortDescriptor alloc] initWithKey:order

ascending:YES];

}

}

[fetchRequest setSortDescriptors:orderArray];

}

if (offset>0) {

[fetchRequest setFetchOffset:offset];

}

if (limit>0) {

[fetchRequest setFetchLimit:limit];

}

return fetchRequest;

}

+(void)filter:(NSString *)predicate orderby:(NSArray *)orders offset:(int)offset limit:(int)limit on:(ListResult)handler{

NSManagedObjectContext *ctx = [[mmDAO instance] createPrivateObjectContext];

[ctx performBlock:^{

NSFetchRequest *fetchRequest = [self makeRequest:ctx predicate:predicate orderby:orders offset:offset limit:limit];

NSError* error = nil;

NSArray* results = [ctx executeFetchRequest:fetchRequest error:&error];

if (error) {

NSLog(@"error: %@", error);

[[mmDAO instance].mainObjectContext performBlock:^{

handler(@[], nil);

}];

}

if ([results count]<1) {

[[mmDAO instance].mainObjectContext performBlock:^{

handler(@[], nil);

}];

}

NSMutableArray *result_ids = [[NSMutableArray alloc] init];

for (NSManagedObject *item  in results) {

NSLog(@"id=%@", item.objectID);

[result_ids addObject:item.objectID];

}

[[mmDAO instance].mainObjectContext performBlock:^{

NSMutableArray *final_results = [[NSMutableArray alloc] init];

for (NSManagedObjectID *oid in result_ids) {

[final_results addObject:[[mmDAO instance].mainObjectContext objectWithID:oid]];

}

handler(final_results, nil);

}];

}];

}

+(id)one:(NSString*)predicate{

NSManagedObjectContext *ctx = [mmDAO instance].mainObjectContext;

NSFetchRequest *fetchRequest = [self makeRequest:ctx predicate:predicate orderby:nil offset:0 limit:1];

NSError* error = nil;

NSArray* results = [ctx executeFetchRequest:fetchRequest error:&error];

if ([results count]!=1) {

raise(1);

}

return results[0];

}

+(void)one:(NSString*)predicate on:(ObjectResult)handler{

NSManagedObjectContext *ctx = [[mmDAO instance] createPrivateObjectContext];

[ctx performBlock:^{

NSFetchRequest *fetchRequest = [self makeRequest:ctx predicate:predicate orderby:nil offset:0 limit:1];

NSError* error = nil;

NSArray* results = [ctx executeFetchRequest:fetchRequest error:&error];

if (error) {

NSLog(@"error: %@", error);

[[mmDAO instance].mainObjectContext performBlock:^{

handler(@[], nil);

}];

}

if ([results count]<1) {

[[mmDAO instance].mainObjectContext performBlock:^{

handler(@[], nil);

}];

}

NSManagedObjectID *objId = ((NSManagedObject*)results[0]).objectID;

[[mmDAO instance].mainObjectContext performBlock:^{

handler([[mmDAO instance].mainObjectContext objectWithID:objId], nil);

}];

}];

}

+(void)delobject:(id)object{

//[[mmDAO instance].mainObjectContext delete:object];

//這裏方法名寫錯了

[[mmDAO instance].mainObjectContext deleteObject:object];

}

@end

本文內容已經打包放在了github，有興趣的能夠fork下來直接用 https://github.com/ipconfiger/asyncCoreDataWrapper

另，文中代碼有兩處錯誤，已經加上了註釋，提早看了的同窗記得以github爲準。