通过表名获取列名，封装数据[FMResultSet]

手机终端开发中，经常会遇到和后台进行大量数据交互的情况，通常情况是json串或者xml串，通常这种key-value形式的数据怎样封装对应到数据表对应的对象呢？

FMDataBase中FMResultSet提供了一个实例方法：

- (void)setupColumnNames {
    
    if (!columnNameToIndexMap) {
        [self setColumnNameToIndexMap:[NSMutableDictionary dictionary]];
    }    
    
    int columnCount = sqlite3_column_count(statement.statement);
    
    int columnIdx = 0;
    for (columnIdx = 0; columnIdx < columnCount; columnIdx++) {
        [columnNameToIndexMap setObject:[NSNumber numberWithInt:columnIdx]
                                 forKey:[[NSString stringWithUTF8String:sqlite3_column_name(statement.statement, columnIdx)] lowercaseString]];
    }
    columnNamesSetup = YES;
}

在这个方法中，对数据库表的列名建立了索引，即可以通过表名，来获取一个FMResultSet对象，进而来建立列名的所以，从而获取到列。

以下是我一个封装的方法：

//根据表名封装数据
- (NSString *) packingSyncDataByTableName:(NSString *) tableName
{
    NSString *theSql=[NSString stringWithFormat:PACKING_DATA_SQL,tableName];
    packedSyncData = [[@"\"" stringByAppendingString:tableName] stringByAppendingString:@"\":"];
    AppDelegate *appDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];
    FMDatabase *database = [[appDelegate fmdb] retain];
    FMResultSet *resultSet=[database executeQuery:theSql];
    [resultSet setupColumnNames];
//    [resultSet resultDict];
    NSEnumerator *columnNames = [resultSet.columnNameToIndexMap keyEnumerator];
    NSString *tempColumnName= nil;
    NSMutableArray *columnNameArray = [[[NSMutableArray alloc] init] autorelease];
    while ((tempColumnName = [columnNames nextObject])) 
    {
        [columnNameArray addObject:tempColumnName];
    }
    NSMutableArray *syncArray = [[[NSMutableArray alloc] init] autorelease];
    NSString *columnName = nil;
    while ([resultSet next]) 
    {
        NSMutableDictionary *syncData = [[[NSMutableDictionary alloc] init] autorelease];
        for(int i =0;i<columnNameArray.count;i++)
        {
            columnName = [columnNameArray objectAtIndex:i];
            NSString *columnValue = [resultSet stringForColumn: columnName];
            if (columnValue==nil) {
                columnValue=@"";
            }
            [syncData setObject:columnValue forKey:columnName];
        }
        [syncArray addObject:syncData];
    }
    if ([syncArray count]==0) {
        return nil;
    }
    packedSyncData =[packedSyncData stringByAppendingString:[syncArray JSONRepresentation]];
    NSLog(@"The packed sync Data is:%@",packedSyncData);
    return packedSyncData;
}