iOS下FMDB的多线程操作（一）

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];
    });
}