iOS学习笔记（十六）——详解数据库操作(使用FMDB)(2)-木庄网络博客

查询操作使用了executeQuery，并涉及到FMResultSet。

if ([db open]) { 
    NSString * sql = [NSString stringWithFormat: 
             @"SELECT * FROM %@",TABLENAME]; 
    FMResultSet * rs = [db executeQuery:sql]; 
    while ([rs next]) { 
      int Id = [rs intForColumn:ID]; 
      NSString * name = [rs stringForColumn:NAME]; 
      NSString * age = [rs stringForColumn:AGE]; 
      NSString * address = [rs stringForColumn:ADDRESS]; 
      NSLog(@"id = %d, name = %@, age = %@ address = %@", Id, name, age, address); 
    } 
    [db close]; 
  }

FMDB的FMResultSet提供了多个方法来获取不同类型的数据：

数据库多线程操作：

如果应用中使用了多线程操作数据库，那么就需要使用FMDatabaseQueue来保证线程安全了。应用中不可在多个线程中共同使用一个FMDatabase对象操作数据库，这样会引起数据库数据混乱。为了多线程操作数据库安全，FMDB使用了FMDatabaseQueue，使用FMDatabaseQueue很简单，首先用一个数据库文件地址来初使化FMDatabaseQueue，然后就可以将一个闭包(block)传入inDatabase方法中。在闭包中操作数据库，而不直接参与FMDatabase的管理。

FMDatabaseQueue * queue = [FMDatabaseQueue databaseQueueWithPath:database_path]; 
  dispatch_queue_t q1 = dispatch_queue_create("queue1", NULL); 
  dispatch_queue_t q2 = dispatch_queue_create("queue2", NULL); 
   
  dispatch_async(q1, ^{ 
    for (int i = 0; i < 50; ++i) { 
      [queue inDatabase:^(FMDatabase *db2) { 
         
        NSString *insertSql1= [NSString stringWithFormat: 
                   @"INSERT INTO '%@' ('%@', '%@', '%@') VALUES (?, ?, ?)", 
                   TABLENAME, NAME, AGE, ADDRESS]; 
         
        NSString * name = [NSString stringWithFormat:@"jack %d", i]; 
        NSString * age = [NSString stringWithFormat:@"%d", 10+i]; 
         
         
        BOOL res = [db2 executeUpdate:insertSql1, name, age,@"济南"]; 
        if (!res) { 
          NSLog(@"error to inster data: %@", name); 
        } else { 
          NSLog(@"succ to inster data: %@", name); 
        } 
      }]; 
    } 
  }); 
   
  dispatch_async(q2, ^{ 
    for (int i = 0; i < 50; ++i) { 
      [queue inDatabase:^(FMDatabase *db2) { 
        NSString *insertSql2= [NSString stringWithFormat: 
                   @"INSERT INTO '%@' ('%@', '%@', '%@') VALUES (?, ?, ?)", 
                   TABLENAME, NAME, AGE, ADDRESS]; 
         
        NSString * name = [NSString stringWithFormat:@"lilei %d", i]; 
        NSString * age = [NSString stringWithFormat:@"%d", 10+i]; 
         
        BOOL res = [db2 executeUpdate:insertSql2, name, age,@"北京"]; 
        if (!res) { 
          NSLog(@"error to inster data: %@", name); 
        } else { 
          NSLog(@"succ to inster data: %@", name); 
        } 
      }]; 
    } 
  });

源码下载：DEMO

标签：SQLite

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