现在ios里使用的数据库一般都是Sqlite，但是使用Sqlite有个不太好的地方就是在多线程的时候，会出现问题，sqlite只能打开一个读或者写连结。这样的话多线程就会碰到资源占用的问题。
最开始是使用FMDB，FMDB的早期版本不能解决这个问题，后来FMDB更新了，新版本的FMDB能够很好的解决这个多线程使用Sqlite 。
FMDB github网址 https://github.com/ccgus/fmdb 最新版的请到github取下载。
本文演示了使用FMDB通过多线程来读和写数据库操作。
1.建立数据库表，我采用的是Firefox的Sqlite manager 来建立的。
建表sql如下
CREATE TABLE "tbl_user" ("_id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL , "name" VARCHAR(30), "password" VARCHAR(30))
2. 建立数据表的映射实体UserEntity
#import <Foundation/Foundation.h> @interface UserEntity : NSObject
{
int _id;
NSString *name;
NSString *password;
} @property (nonatomic, assign)int ID;
@property (nonatomic, retain) NSString *name;
@property (nonatomic, retain) NSString *password;
@end
3. 建立操作数据库的dao
//
// DbDao.m
// SqliteTest
//
// Created by foxwang on 12-4-9.
// Copyright (c) 2012年 __MyCompanyName__. All rights reserved.
// #import "DbDao.h"
#import "DbFileManager.h" #import "FMDatabase.h"
#import "FMDatabaseAdditions.h"
#import "FMDatabasePool.h"
#import "FMDatabaseQueue.h"
#import "UserEntity.h" static DbDao *gSharedInstance = nil; @implementation DbDao
@synthesize dbFile;
@synthesize dbQueue; +(DbDao *)sharedInstance
{
@synchronized(self)
{
if (gSharedInstance == nil)
gSharedInstance = [[DbDao alloc] init];
}
return gSharedInstance;
} - (void)dealloc
{
[self.dbFile release];
self.dbQueue = nil;
[super dealloc];
} - (id)init
{
self = [super init];
if (self)
{
self.dbFile = [DbFileManager dbFilePath];
self.dbQueue = [FMDatabaseQueue databaseQueueWithPath:self.dbFile];
}
return self;
} - (UserEntity *)rsToUser:(FMResultSet*)rs
{
UserEntity *user = [[[UserEntity alloc] init] autorelease];
user.ID = [rs intForColumn:@"_id"];
user.name = [rs stringForColumn:@"name"];
user.password = [rs stringForColumn:@"password"];
return user;
} - (void)addUser:(UserEntity *)user
{
[self.dbQueue inTransaction:^(FMDatabase *db, BOOL *rollback) {
[db open];
NSString *sql = @"insert into tbl_user(name, password) values (?, ?)";
[db executeUpdate:sql,user.name, user.password];
[db close];
}];
} - (NSArray *)getUsers;
{
__block NSMutableArray *users = [[[NSMutableArray alloc] init] autorelease];
[self.dbQueue inDatabase:^(FMDatabase *db) {
[db open];
NSString *sql = @"select * from tbl_user ";
FMResultSet *rs = [db executeQuery:sql];
while ([rs next])
{
[users addObject:[self rsToUser :rs]];
}
[db close];
}];
return users;
}
@end
4. 编写测试方法
在didFinishLaunchingWithOptions 方法里启动3个线程 ：2个线程写，1个线程读
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
self.window = [[[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]] autorelease];
// Override point for customization after application launch.
self.viewController = [[[ViewController alloc] initWithNibName:@"ViewController" bundle:nil] autorelease];
self.window.rootViewController = self.viewController;
[self.window makeKeyAndVisible];
[NSThread detachNewThreadSelector:@selector(writeDbOne) toTarget:self withObject:nil];
[NSThread detachNewThreadSelector:@selector(readDb) toTarget:self withObject:nil];
[NSThread detachNewThreadSelector:@selector(writeDbTwo) toTarget:self withObject:nil];
return YES;
}
- (void)writeDbOne
{
DbDao *dao = [DbDao sharedInstance];
for (int i = 0; i < 500; i++)
{
@autoreleasepool
{
UserEntity *user = [[[UserEntity alloc] init] autorelease];
user.name = [NSString stringWithFormat:@"name %d", i];
user.password = [NSString stringWithFormat:@"password %d", i];
[dao addUser:user];
NSLog(@"writeDbOne %d ", i);
}
}
} - (void)writeDbTwo
{
DbDao *dao = [DbDao sharedInstance];
for (int i = 600; i < 1200; i++)
{
@autoreleasepool
{
UserEntity *user = [[[UserEntity alloc] init] autorelease];
user.name = [NSString stringWithFormat:@"name %d", i];
user.password = [NSString stringWithFormat:@"password %d", i];
[dao addUser:user];
NSLog(@"writeDbTwo %d ", i);
}
}
} - (void)readDb
{
DbDao *dao = [DbDao sharedInstance];
NSArray *users = [dao getUsers];
NSLog(@"%@", users);
}
最后查看数据库信息，数据成功插入
结论 ：使用新的FMDB ，很好的解决了多线程问题