iOS下FMDB的多线程操作（一）

本文主要是介绍iOS下FMDB的多线程操作（一），希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

iOS中一些时间比较长的操作都应该放在子线程中，以避免UI的卡顿。而sqlite 是非线程安全的，故在多线程中不能共用同一个数据库连接，否则会导致EXC_BAD_ACCESS。所以我们可以在子线程中创建一个新的db连接（新建一个db对象），然后再操作数据库。

如果选择FMDB，除了以上所说的方式外，还可以利用FMDatabaseQueue来解决多线程问题。

关于FMDB的使用网上教程比较多，内容基本都是与唐巧的这篇http://www.devtang.com/blog/2012/04/22/use-fmdb/差不多

这里记录一下多线程下的使用。

方式一：采用每次新建db的方式

db路径我是写了一个方法

+ (NSString *)getDBPath
{NSString* docsdir = [NSSearchPathForDirectoriesInDomains( NSDocumentDirectory, NSUserDomainMask, YES) lastObject];NSFileManager *filemanage = [NSFileManager defaultManager];docsdir = [docsdir stringByAppendingPathComponent:@"FMDBDemo"];BOOL isDir;BOOL exit =[filemanage fileExistsAtPath:docsdir isDirectory:&isDir];if (!exit || !isDir) {[filemanage createDirectoryAtPath:docsdir withIntermediateDirectories:YES attributes:nil error:nil];}NSString *dbpath = [docsdir stringByAppendingPathComponent:@"myDB.sqlite"];return dbpath;
}

1、创建数据库表

/** 创建表 */
+ (BOOL)createUserTableByDB
{FMDatabase *db = [FMDatabase databaseWithPath:[self getDBPath]];if (![db open]) {NSLog(@"数据库打开失败!");return NO;}NSString *sql = @"CREATE TABLE IF NOT EXISTS User(ID INTEGER PRIMARY KEY, name TEXT, age INTEGER, ID_No TEXT);";BOOL res = [db executeUpdate:sql];if (res) {NSLog(@"创建表格成功");}else {NSLog(@"创建表格失败");}return res;
}

2、插入数据

插入数据，我分了两种情形，一种是单条插入，一种是利用事务（利用事务插入多条时，时间会快很多，而且有任何一条插入失败，则不会提交到数据库）

/** 保存单个对象 */
- (BOOL)saveByDB
{FMDatabase *db = [FMDatabase databaseWithPath:[User getDBPath]];if (![db open]) {NSLog(@"数据库打开失败!");return NO;}NSString *sql = [NSString stringWithFormat:@"INSERT INTO User(name, age, ID_No) VALUES ('%@', '%d', '%@');", self.name, self.age, self.ID_no];BOOL res = [db executeUpdate:sql];[db close];if (res) {NSLog(@"插入数据成功");}else {NSLog(@"插入数据失败");}return res;
}/** 批量保存用户对象 */
+ (BOOL)saveObjectsByDB:(NSArray *)array
{FMDatabase *db = [FMDatabase databaseWithPath:[self getDBPath]];if (![db open]) {NSLog(@"数据库打开失败!");return NO;}[db beginTransaction];BOOL isRollBack = NO;@try {for (User *user in array) {NSString *sql = [NSString stringWithFormat:@"INSERT INTO User(name, age, ID_No) VALUES ('%@', '%d', '%@');", user.name, user.age, user.ID_no];BOOL res = [db executeUpdate:sql];if (!res) {NSLog(@"db事务插入失败");}else {NSLog(@"db事务插入成功");}}}@catch (NSException *exception) {isRollBack = YES;[db rollback];}@finally {if (!isRollBack) {[db commit];}}[db close];return !isRollBack;
}

更新与删除也分两种情形，与插入类似。

3、更新数据

/** 更新单个对象 */
- (BOOL)updateByDB
{FMDatabase *db = [FMDatabase databaseWithPath:[User getDBPath]];if (![db open]) {NSLog(@"数据库打开失败!");return NO;}NSString *sql = [NSString stringWithFormat:@"UPDATE User SET name = '%@',age = '%d',ID_no = '%@' WHERE ID = '%d';", self.name, self.age, self.ID_no, self.ID];BOOL res = [db executeUpdate:sql];[db close];if (res) {NSLog(@"插入数据成功");}else {NSLog(@"插入数据失败");}return res;
}/** 批量更新用户对象*/
+ (BOOL)updateObjectsByDB:(NSArray *)array
{FMDatabase *db = [FMDatabase databaseWithPath:[User getDBPath]];if (![db open]) {NSLog(@"数据库打开失败!");return NO;}[db beginTransaction];BOOL isRollBack = NO;@try {for (User *user in array) {NSString *sql = [NSString stringWithFormat:@"UPDATE User SET name = '%@',age = '%d',ID_no = '%@' WHERE ID = '%d';", user.name, user.age, user.ID_no, user.ID];BOOL res = [db executeUpdate:sql];if (!res) {NSLog(@"db事务更新失败");}else {NSLog(@"db事务更新成功");}}}@catch (NSException *exception) {isRollBack = YES;[db rollback];}@finally {if (!isRollBack) {[db commit];}}[db close];return !isRollBack;
}

4、删除数据

/** 删除单个对象 */
- (BOOL)deleteObjectByDB
{FMDatabase *db = [FMDatabase databaseWithPath:[User getDBPath]];if (![db open]) {NSLog(@"数据库打开失败!");return NO;}NSString *sql = [NSString stringWithFormat:@"DELETE FROM User WHERE ID = '%d'",self.ID];BOOL res = [db executeUpdate:sql];[db close];if (res) {NSLog(@"删除数据成功");}else {NSLog(@"删除数据失败");}return res;
}/** 批量删除用户对象 */
+ (BOOL)deleteObjectsByDB:(NSArray *)array
{FMDatabase *db = [FMDatabase databaseWithPath:[self getDBPath]];if (![db open]) {NSLog(@"数据库打开失败!");return NO;}[db beginTransaction];BOOL isRollBack = NO;@try {for (User *user in array) {NSString *sql = [NSString stringWithFormat:@"DELETE FROM User WHERE ID = '%d'",user.ID];BOOL res = [db executeUpdate:sql];if (!res) {NSLog(@"db事务删除失败");}else {NSLog(@"db事务删除成功");}}}@catch (NSException *exception) {isRollBack = YES;[db rollback];}@finally {if (!isRollBack) {[db commit];}}[db close];return !isRollBack;
}

5、查询数据

查询就比较简单了。

/** 查询全部用户 */
+ (NSArray *)findAllByDB
{FMDatabase *db = [FMDatabase databaseWithPath:[self getDBPath]];if (![db open]) {NSLog(@"数据库打开失败!");return nil;}NSMutableArray *users = [[NSMutableArray alloc] init];NSString *sql = @"SELECT * FROM User";FMResultSet *resultSet = [db executeQuery:sql];while ([resultSet next]) {User *user = [[User alloc] init];user.ID = [resultSet intForColumn:@"ID"];user.name = [resultSet stringForColumn:@"name"];user.age = [resultSet intForColumn:@"age"];user.ID_no = [resultSet stringForColumn:@"ID_no"];[users addObject:user];[user release];}NSLog(@"查询全部成功");return [users autorelease];
}/** 查找某个用户 */
+ (instancetype)findFirstBySqlByDB:(NSString *)sql
{User *user = nil;NSArray *users = [self findBySqlByDB:sql];if (users.count > 0) {user = [users firstObject];}return user;
}/** 查找用户 */
+ (NSArray *)findBySqlByDB:(NSString *)sql
{FMDatabase *db = [FMDatabase databaseWithPath:[self getDBPath]];if (![db open]) {NSLog(@"数据库打开失败!");return nil;}NSMutableArray *users = [[NSMutableArray alloc] init];NSString *select = @"SELECT * FROM User ";if (sql) {select = [select stringByAppendingString:sql];}FMResultSet *resultSet = [db executeQuery:select];while ([resultSet next]) {User *user = [[User alloc] init];user.ID = [resultSet intForColumn:@"ID"];user.name = [resultSet stringForColumn:@"name"];user.age = [resultSet intForColumn:@"age"];user.ID_no = [resultSet stringForColumn:@"ID_no"];[users addObject:user];[user release];}NSLog(@"条件查询成功");return [users autorelease];
}

而多线程下的调用方式是这样的，其中上面的所有方法都是在对象类User中。

/** 用db插入User数据*/
- (IBAction)dbInsertData:(id)sender {//多线程插入数据for (int i = 0; i < 5; i++) {dispatch_async(dispatch_get_global_queue(0, 0), ^{User *user = [[User alloc] init];user.name = @"dbName一";user.ID_no = [NSString stringWithFormat:@"%d",55555+i];user.age = 555+i;[user saveByDB];});}//利用事务插入数据dispatch_async(dispatch_get_global_queue(0, 0), ^{NSMutableArray *array = [NSMutableArray array];for (int i = 0; i < 5; i++) {User *user = [[User alloc] init];user.name = @"db事务";user.ID_no = [NSString stringWithFormat:@"%d",66666+i];user.age = 66+i;[array addObject:user];[user release];}[User saveObjectsByDB:array];});
}

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