FMDB的初体验及离线缓存

一、FMDB的简单使用

1、代码实例

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1、准备工作     需要导入sqlite3框架，下载fmdb类库 2、打开数据库与创建表    //2.1存取的沙盒路径  NSString *cache = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES).lastObject;     NSString *filePath = [cache stringByAppendingPathComponent:@"class.sqlite"];     //2.2打开数据库     FMDatabase *base =[FMDatabase databaseWithPath:filePath];     if([base open]){         NSLog(@"打开成功");     }else{         NSLog(@"打开失败");     }     //2.3创建表     NSString *sql = @"create table if not exists t_students (id integer primary key autoincrement,name text ,age integer,height real)";     BOOL flag = [base executeUpdate:sql];     if (flag) {         NSLog(@"创建表成功");     }else{         NSLog(@"创建表失败");     }     _dataBase = base;  //赋值全局变量 3、凡是增、删、改都行executeUpdate执行语句。 4、插入数据 //插入数据，注意当数据为整型或浮点型时，必须转换成NSNumber类型的，@(),包含起来     for (NSInteger i = 0; i< 10; i++) {         NSString *name = [NSString stringWithFormat:@"TheYouth%ld",i];         NSInteger age = [[NSString stringWithFormat:@"%ld",i+20] integerValue];         float height = [[NSString stringWithFormat:@"%.1f",i+0.5] floatValue];                   BOOL isflag = [_dataBase executeUpdate:@"insert into t_students (name,age,height) values (?,?,?)",name,@(age),@(height)];         if (isflag) {             NSLog(@"插入表成功");         }else{             NSLog(@"插入表失败");         }     } 5、删除数据  BOOL isflag = [_dataBase executeUpdate:@"delete from t_students where age > 25"];     if (isflag) {         NSLog(@"删除成功");     }else{         NSLog(@"删除失败");     } 6、修改数据 BOOL isflag = [_dataBase executeUpdate:@"update t_students set age = 3.8,name='xingZai' where height < 3.5"];     if (isflag) {         NSLog(@"修改成功");     }else{         NSLog(@"修改失败");     } 7、查询数据  FMResultSet *result = [_dataBase executeQuery:@"select * from t_students"];     while ([result next]) { //执行符合条件的下一行         NSString *name = [result stringForColumnIndex:1]; //取出字符型属性         NSInteger age = [result intForColumnIndex:2];  //取出整型         CGFloat height = [result doubleForColumnIndex:3]; //取出浮点型数据         NSLog(@"%@,%ld,%.1f",name,age,height);     }

二、FMDB多线程与事务

1、代码实例

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//1.创建数据库，打开表 NSString *cachePath = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES)[0];     //设置路径     NSString *filePath = [cachePath stringByAppendingPathComponent:@"student.sqlite"];     // 创建数据库实例     FMDatabaseQueue *queue = [FMDatabaseQueue databaseQueueWithPath:filePath];     _queue = queue;           // 创建数据库表     // 提供了一个多线程安全的数据库实例     [queue inDatabase:^(FMDatabase *db) {                 BOOL flag =  [db executeUpdate:@"create table if not exists t_student (id integer primary key autoincrement,name text,money integer)"];         if (flag) {             NSLog(@"success");         }else{             NSLog(@"failure");         }      }]; //2.插入数据  [_queue inDatabase:^(FMDatabase *db) {        BOOL flag = [db executeUpdate:@"insert into t_student (name,money) values (?,?)",@"a",@100];         if (flag) {             NSLog(@"success");         }else{             NSLog(@"failure");         }         [db executeUpdate:@"insert into t_student (name,money) values (?,?)",@"b",@50];               }]; //3.删除所有数据    [_queue inDatabase:^(FMDatabase *db) {         BOOL flag = [db executeUpdate:@"delete from t_user;"];         if (flag) {             NSLog(@"success");         }else{             NSLog(@"failure");         }     }]; //4.开启一个事务，来处理多线程的问题，必须全部处理完才能结束(成功)，否则失败，然后回滚到原始状态   [_queue inDatabase:^(FMDatabase *db) {         // 开启事务         [db beginTransaction];        BOOL flag = [db executeUpdate:@"update t_user set money = ? where name = ?;",@500,@"a"];         if (flag) {             NSLog(@"success");         }else{             NSLog(@"failure");             // 回滚             [db rollback];         }         BOOL flag1 = [db executeUpdate:@"updat t_user set money = ? where name = ?;",@1000,@"b"];         if (flag1) {             NSLog(@"success");         }else{             NSLog(@"failure");             [db rollback];         }         // 全部操作完成时候再去         [db commit];     }];

三、FMDB处理离线缓存

1、思维导图

2、代码实例

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以微博数据为例 1、保存数据 + (void)saveWithStatuses:(NSArray *)statuses {//取出数据     // 遍历模型数组     for (NSDictionary *statusDict in statuses) {//遍历数组中的每个字典         NSString *idstr = statusDict[@"idstr"]; //存取idstr，为了之后取数据         NSString *accessToken = [CZAccountTool account].access_token; //存取用户token         NSData *data = [NSKeyedArchiver archivedDataWithRootObject:statusDict]; //存取字典数据，转换成二进制流        BOOL flag = [_db executeUpdate:@"insert into t_status (idstr,access_token,dict) values(?,?,?)",idstr,accessToken,data];//插入数据，字段有idstr，用户token，原始数据字典         if (flag) {             NSLog(@"插入成功");         }else{             NSLog(@"插入失败");         }     } } //2.存数据库中取数据，param状态模型，要不需要传很多参数 + (NSArray *)statusesWithParam:(CZStatusParam *)param {     // 进入程序第一次获取的查询语句     NSString *sql = [NSString stringWithFormat:@"select * from t_status where access_token = '%@' order by idstr desc limit 20;",param.access_token];     if (param.since_id) { // 获取最新微博的查询语句         sql = [NSString stringWithFormat:@"select * from t_status where access_token = '%@' and idstr > '%@' order by idstr desc limit 20;",param.access_token,param.since_id];     }else if (param.max_id){  // 获取更多微博的查询语句         sql = [NSString stringWithFormat:@"select * from t_status where access_token = '%@' and idstr <= '%@' order by idstr desc limit 20;",param.access_token,param.max_id];     }     FMResultSet *set = [_db executeQuery:sql];     NSMutableArray *arrM = [NSMutableArray array];     while ([set next]) {         NSData *data = [set dataForColumn:@"dict"];         NSDictionary *dict = [NSKeyedUnarchiver unarchiveObjectWithData:data];         CZStatus *s = [CZStatus objectWithKeyValues:dict];         [arrM addObject:s];     }     return arrM; }