Objective c 从iPhone应用程序的数据库读取FMDB

我正在使用以下代码从customers表中读取记录。由于某些原因，返回的结果集总是空的

    -(NSMutableArray *) getCustomers
{
    NSMutableArray *customers = [[NSMutableArray alloc] init];

    NSString *databaseName = @"Customers.db";

    NSArray *documentsPath = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); 
    NSString *documentsDir = [documentsPath objectAtIndex:0];

    NSString *databasePath = [documentsDir stringByAppendingPathComponent:databaseName];

    FMDatabase *db = [FMDatabase databaseWithPath:databasePath];

    if(![db open]) 
    {
        return nil; 
    }

    FMResultSet *results = [db executeQuery:@"SELECT * FROM customers"];

    while([results next]) 
    {
        Customer *customer = [[Customer alloc] init];


        customer.firstName = [results stringForColumn:@"firstname"];
        customer.lastName = [results stringForColumn:@"lastname"];

        [customers addObject:customer];

    }

    [db close];

    return customers; 


}

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我多次检查数据库，它显示了数据，但由于某种原因，FMDB无法检索数据

将db log errors设置为true，这将显示您可以在控制台中找到问题所在的位置

FMDatabase *db = [FMDatabase databaseWithPath:databasePath];
db.logsErrors = YES;