Question

我无法从FMDB捕获空结果集。代码如下。我从数据库打开和关闭以及NSLog“1”获取NSLog，但是在If语句中没有一个！如果我在数据库中有数据就可以了，但我想在数据库为空时捕获并编辑结果。

    [self openDatabase];

NSNumberFormatter *nfcurrency = [[NSNumberFormatter alloc]init];
[nfcurrency setNumberStyle:NSNumberFormatterCurrencyStyle];
[nfcurrency setLocale:[NSLocale currentLocale]];

FMResultSet *result = [[self getDatabase]executeQuery:@"SELECT BFNeeded FROM tblBets ORDER BY pk DESC LIMIT 1,1;"];
//FMResultSet *result = [[self getDatabase]executeQuery:@"SELECT BFNeeded FROM tblBets ORDER BY pk DESC LIMIT 1,1;"];
NSLog(@"1");
if (result == NULL) {
    NSLog(@"Last BFNeeded Result = nil");
} else {
    while ([result next]) {
        NSLog(@"HERE");
        NSString *lastBFNeeded = [nfcurrency stringFromNumber:[NSNumber numberWithDouble:[result doubleForColumn:@"BFNeeded"]]];
        NSLog(@"lastBFNeeded=%@",lastBFNeeded);
    }
}

NSLog(@"ClosingDB");
[self closeDatabase];

获得第一次回复后继续：

我无法让hasAnotherRow按预期工作。我有这段代码：

FMResultSet *result = [[self getDatabase]executeQuery:@"SELECT BFNeeded FROM tblBets ORDER BY pk DESC LIMIT 0,1;"];

if (result == nil) {
    NSLog(@"Last BFNeeded Result = nil");
}
else {
    NSLog(@"has results1: %@", [result hasAnotherRow] ? @"YES" : @"NO");
    while ([result next]) {
        NSLog(@"has results2: %@", [result hasAnotherRow] ? @"YES" : @"NO");
    }
}

使用返回结果的数据库，我得到result1 NO，result2 YES，所以我假设hasAnotherRow必须进入while（[result next]）循环。但是对于一个空数据库，我得到result1 NO，它甚至没有得到result2！

Answer 1

对于产生0行的查询，“result”永远不会为nil。

另外，您不应将对象指针与NULL进行比较 - 与nil进行比较。请参阅此问题：NULL vs nil in Objective-C

试试这个：

FMResultSet *result = [[self getDatabase]executeQuery:@"SELECT BFNeeded FROM tblBets ORDER BY pk DESC LIMIT 1,1;"];

NSLog ( @"has results: %@", [result hasAnotherRow] ? @"YES" : @"NO" );

Answer 2

NSInteger count;

query=[NSString stringWithFormat:@"select Count(*) from %@  where name = 'brandon' ",dbName];
results = [database executeQuery:query ];
while([results next]) {
    count  = [results intForColumnIndex:0];
    NSLog(@"count:%d",count);
}

如果没有条目，

将设置等于零

我无法捕获FMDB空结果集

2 个答案: