数据存储_FMDB数据库队列

一、代码示例

1.需要先导入FMDB框架和头文件，由于该框架依赖于libsqlite库，所以还应该导入该库。

2.代码如下：

 1 //

 2 //  YYViewController.m

 3 //  05-FMDB数据库队列

 4 //

 5 //  Created by apple on 14-7-28.

 6 //  Copyright (c) 2014年 wendingding. All rights reserved.

 7 //

 8

 9 #import "YYViewController.h"

10 #import "FMDB.h"

11

12 @interface YYViewController ()

13 @property(nonatomic,strong)FMDatabaseQueue *queue;

14 @end

15

16 @implementation YYViewController

17

18 - (void)viewDidLoad

19 {

20     [super viewDidLoad];

21

22     //1.获得数据库文件的路径

23     NSString *doc=[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];

24     NSString *fileName=[doc stringByAppendingPathComponent:@"person.sqlite"];

25

26     //2.获得数据库队列

27     FMDatabaseQueue *queue=[FMDatabaseQueue databaseQueueWithPath:fileName];

28 //    FMDatabase *db=[FMDatabase databaseWithPath:fileName];

29

30     //3.打开数据库

31     [queue inDatabase:^(FMDatabase *db) {

32          BOOL result=[db executeUpdate:@"CREATE TABLE IF NOT EXISTS t_person (id integer PRIMARY KEY AUTOINCREMENT, name text NOT NULL, age integer NOT NULL);"];

33         if (result) {

34             NSLog(@"创表成功");

35         }else

36         {

37             NSLog(@"创表失败");

38         }

39     }];

40     self.queue=queue;

41

42 }

43

44 -(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event

45 {

46     //插入数据

47 //    [self.queue inDatabase:^(FMDatabase *db) {

48 //        [db executeUpdate:@"INSERT INTO t_person (name, age) VALUES (?, ?);",@"wendingding", @22];

49 //    }];

50

51     //查询数据

52     [self.queue inDatabase:^(FMDatabase *db) {

53         // 1.执行查询语句

54         FMResultSet *resultSet = [db executeQuery:@"SELECT * FROM t_person"];

55

56         // 2.遍历结果

57         while ([resultSet next]) {

58             int ID = [resultSet intForColumn:@"id"];

59             NSString *name = [resultSet stringForColumn:@"name"];

60             int age = [resultSet intForColumn:@"age"];

61             NSLog(@"%d %@ %d", ID, name, age);

62         }

63     }];

64

65 }

66

67 @end

先插入数据，之后查询结果，打印如下：

数据存储_FMDB数据库队列

3.代码说明

有了一个队列对象，它的内部自动就拥有一个数据库对象，且数据库的操作是线程安全的。

二、事务

事务，没有事务的话会出现问题。

举例：银行的例子

张三和李四账户都有1000块钱，如果张三要转账给李四，需要执行两条SQL语句，考虑到安全性，要求这两条语句要么全部执行成功，要么全部执行失败。

事务：把多条语句放到同一个事务中，要么全部成功，要么全部失败（如果中途出现问题，那么会自动回滚）。事务的执行具有原子性。

　　事务代码处理：

　　把多条语句添加到一个事务中去执行：

1    //插入数据

2     [self.queue inDatabase:^(FMDatabase *db) {

3         [db beginTransaction];

4         [db executeUpdate:@"INSERT INTO t_person (name, age) VALUES (?, ?);",@"wendingding", @22];

5         [db executeUpdate:@"INSERT INTO t_person (name, age) VALUES (?, ?);",@"wendingding", @23];

6         [db executeUpdate:@"INSERT INTO t_person (name, age) VALUES (?, ?);",@"wendingding", @24];

7         [db executeUpdate:@"INSERT INTO t_person (name, age) VALUES (?, ?);",@"wendingding", @25];

8         [db commit];

9     }];

如果中途出现问题，那么会自动回滚（重新开始），也可以选择手动回滚。

 1     //插入数据

 2     [self.queue inDatabase:^(FMDatabase *db) {

 3         [db beginTransaction];

 4         [db executeUpdate:@"INSERT INTO t_person (name, age) VALUES (?, ?);",@"wendingding", @22];

 5         [db executeUpdate:@"INSERT INTO t_person (name, age) VALUES (?, ?);",@"wendingding", @23];

 6         [db executeUpdate:@"INSERT INTO t_person (name, age) VALUES (?, ?);",@"wendingding", @24];

 7         [db rollback];

 8         [db executeUpdate:@"INSERT INTO t_person (name, age) VALUES (?, ?);",@"wendingding", @25];

 9         [db commit];

10     }];

上面的代码。前三条插入语句是作废的。

事务处理的另一种方式：

1    [self.queue inTransaction:^(FMDatabase *db, BOOL *rollback) {

2         [db executeUpdate:@"INSERT INTO t_person (name, age) VALUES (?, ?);",@"wendingding", @22];

3         [db executeUpdate:@"INSERT INTO t_person (name, age) VALUES (?, ?);",@"wendingding", @23];

4         [db executeUpdate:@"INSERT INTO t_person (name, age) VALUES (?, ?);",@"wendingding", @24];

5     }];

具体可以参考FMDB官方文档：

使用FMDatabaseQueue 及线程安全

在多个线程中同时使用一个FMDatabase实例是不明智的。现在你可以为每个线程创建一个FMDatabase对象。不要让多个线程分享同一个实例，它无法在多个线程中同时使用。所以，不要初始化FMDatabase对象，然后在多个线程中使用。请使用 FMDatabaseQueue，它是你的朋友而且会帮助你。以下是使用方法：

首先创建队列。

FMDatabaseQueue *queue = [FMDatabaseQueue databaseQueueWithPath:aPath];

这样使用(简单的使用，非事务)

[queue inDatabase:^(FMDatabase *db) {
[db executeUpdate:@"INSERT INTO myTable VALUES (?)", [NSNumber numberWithInt:1]];
[db executeUpdate:@"INSERT INTO myTable VALUES (?)", [NSNumber numberWithInt:2]];
[db executeUpdate:@"INSERT INTO myTable VALUES (?)", [NSNumber numberWithInt:3]];
FMResultSet *rs = [db executeQuery:@"select * from foo"];
while([rs next]) {
…
}
}];

像这样，轻松地把简单任务包装到事务里：

[queue inTransaction:^(FMDatabase *db, BOOL *rollback) {
[db executeUpdate:@"INSERT INTO myTable VALUES (?)", [NSNumber numberWithInt:1]];
[db executeUpdate:@"INSERT INTO myTable VALUES (?)", [NSNumber numberWithInt:2]];
[db executeUpdate:@"INSERT INTO myTable VALUES (?)", [NSNumber numberWithInt:3]];
if (whoopsSomethingWrongHappened) { //有什么错误发生的话，回滚
*rollback = YES; return;
}
// etc…
[db executeUpdate:@"INSERT INTO myTable VALUES (?)", [NSNumber numberWithInt:4]];
}];

FMDatabaseQueue 后台会建立系列化的G-C-D队列，并执行你传给G-C-D队列的块。这意味着你从多线程同时调用调用方法，GDC也会按它接收的块的顺序来执行。

whoopsSomethingWrongHappened是什么鬼？？？？？看一下下面的demo

#pragma mark - 数据存储文件的路径

- (NSString *)dbPathTest {

NSString *string = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) firstObject];

NSString *stringPath = [string stringByAppendingPathComponent:@"test.sqlite"];

NSLog(@"%@",stringPath);

return stringPath;

}

#pragma mark - 多线程操作数据库时,事务的处理方式

- (void)threadTransaction {

//创建队列

FMDatabaseQueue *queue = [FMDatabaseQueue databaseQueueWithPath:[self dbPathTest]];

__block BOOL whoopsSomethingWrongHappened = true;

//把任务包装到事务里

[queue inTransaction:^(FMDatabase *db, BOOL *rollback) {

whoopsSomethingWrongHappened &= [db executeUpdate:@"insert into myTable values(?)",[NSNumber numberWithInt:1]];

whoopsSomethingWrongHappened &= [db executeUpdate:@"insert into myTable values(?)",[NSNumber numberWithInt:2]];

whoopsSomethingWrongHappened &= [db executeUpdate:@"insert into myTabl values(?)",[NSNumber numberWithInt:3]];

//如果有错误返回

if(!whoopsSomethingWrongHappened) {

*rollback = YES;

return;

}

NSLog(@"hello,yoowei");

}];

}

还可以看一下其他的demo中的写法：

- (void)saveChangesInBackground:(void (^)())complete {

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

FMDatabaseQueue *queue = [FMDatabaseQueue databaseQueueWithPath:self.schema.storage];

[queue inTransaction:^(FMDatabase *db, BOOL *rollback) {

@try {

for (FMDTObject *entry in self.dataArray) {

NSArray *array = [self getObjectValues:entry];

NSString *statement = nil;

if (self.relpace) {

statement = self.schema.statementReplace;

} else {

statement = self.schema.statementInsert;

}

[db executeUpdate:statement withArgumentsInArray:array];

}

@catch (NSException *exception) {

*rollback = YES;

}

[self.dataArray removeAllObjects];

if (complete) {

complete();

}

}];

});

}

- (void)threadNoTransaction {

FMDatabaseQueue *queue = [FMDatabaseQueue databaseQueueWithPath:[self dbPathTest]];

[queue inDatabase:^(FMDatabase *db) {

[db beginTransaction];

BOOL isRollBack = NO;

@try {

for (int i = 0; i<5; i++) {

NSString *roomID= [[NSString alloc] initWithFormat:@"roomid_%d",i];

NSString *sql= @"insert into myTable values(?)";

BOOL a = [db executeUpdate:sql,roomID];

if (!a) {

NSLog(@"插入失败1");

}

@catch (NSException *exception) {

isRollBack = YES;

[db rollback];

}

@finally {

if (!isRollBack) {

[db commit];

}

}];

}

参考链接：

http://www.cnblogs.com/wendingding/p/3873874.html

https://github.com/ccgus/fmdb

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数据存储_FMDB数据库队列

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