cannot fetch value from sqlite in IOS - ios

Question

Table values:
ID=1 CUSTOMERID=1 NAME=John EMAIL=email USERNAME=usernaeme
I am using this code to fetch customerId from Usertable with this code
#try {
//CustomerIdField=#"admin";
// customerUsername=#"admin";
NSLog(#"the value of customerusername is %#",customerUsername);
NSArray *dirPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *docsDir = [dirPaths objectAtIndex:0];
NSLog(#"inside function");
databasePath = [[NSString alloc] initWithString: [docsDir stringByAppendingPathComponent: #"EBook.db" ]];
const char *dbpath;
#try {
dbpath = [databasePath UTF8String];
NSLog(#"the const char is %s",dbpath);
}
#catch (NSException *exception) {
NSLog(#"the exception3 is %#",exception);
}
if (sqlite3_open(dbpath, &Ebookreaderdb) == SQLITE_OK)
{
NSString *selectSQL = [NSString stringWithFormat: #"SELECT CUSTOMERID FROM Usertable WHERE EMAIL=\"%#\"",customerUsername];
sqlite3_stmt *selstatement;
const char *select_stmt = [selectSQL UTF8String];
//NSMutableArray *resultArray = [[NSMutableArray alloc]init];
if (sqlite3_prepare_v2(Ebookreaderdb,
select_stmt, -1, &selstatement, NULL ) == SQLITE_OK)
{
NSLog(#"inside sqlite OK"); //this prints in log
if (sqlite3_step(selstatement) == SQLITE_ROW)
{
NSLog(#"inside sqlite ROW"); // this is also printing in log
NSString *userInfoStr = [NSString stringWithUTF8String:(char *)sqlite3_column_text(selstatement,1)];
NSLog(#"val is %#",userInfoStr);
char *tmp = sqlite3_column_text(selstatement,1);
if (tmp == NULL)
CustomerIdField = nil;
else
CustomerIdField = [[NSString alloc] initWithUTF8String:tmp];
CustomerIdField = [[NSString alloc] initWithUTF8String:
(const char *) sqlite3_column_text(selstatement,1)];
NSLog(#"inside customer is %#",CustomerIdField);
// [resultArray addObject:name];
}
else{
NSLog(#"Not found");
// return nil;
}
sqlite3_reset(selstatement);
}
But i am getting this exception Newpjtonfriday[2165:84017] the exception is 2 *** +[NSString stringWithUTF8String:]: NULL cString
I googled with the above result and everywhere it is saying that the value is null that is why the exception occurs. but in my case the value is there.
Because the code
NSLog(#"inside sqlite ROW");
is coming in log meaning that a row exists in table. But cannot fetch it.
Please help

Answer 1

I think it's a typo:
#"SELECT CUSTOMERID FROM Usertable WHERE EMAIL=\"%#\"",customerUsername;
You are passing the username instead of the e-mail? Or maybe you meant to SELECT ... WHERE USERNAME=?
Also there is no need for any of those #try/#catch blocks as I cannot see how an Objective-C exception can be thrown by that code.
One last thing; in order to avoid SQL Injection attacks you should bind the values into your statements, rather than formatting them as a string, as you have done here.

Answer 2

Little advise if you are just starting to develop on iOS, try to use some library(FMDB to easy work with SQLite) to make some task more straight forward.
Answer to your Question
Try the "SELECT * FROM Usertable" if it has any row in your table.
Second you should check if the value in your row is not NULL.
To get easy solution use something like Datum SQLite Free(Mac os X) OR you could use SELECT COUNT to ensure you have any rows in table.
Try your select and if the app return the rows but there is no value in your column that's mean you have problems with write to DB logic but not in read logic and you are trying to fetch row with have null value on column you want.That's why this method is not working:
[NSString stringWithUTF8String:]: NULL cString
its thrown an exception because you have no string and trying to send NULL to method.

Answer 3

The sqlite3_column_text index number is zero-based, not one-based. Thus, this line:
char *tmp = sqlite3_column_text(selstatement, 1);
Should be:
char *tmp = sqlite3_column_text(selstatement, 0);
By the way, your handling of this tmp variable is a prudent way of checking to make sure it's not NULL before you use it. Unfortunately, elsewhere in this same routine you use sqlite3_column_text value directly (which is why your app crashed, rather than gracefully reporting the error). You have several redundant calls to sqlite3_column_text here. I would suggest employing the pattern you used with this tmp variable.

Answer 4

Let me give you my suggestion I tried what you just did and I also got the error. Then I did some googling and found this link
http://www.raywenderlich.com/913/sqlite-tutorial-for-ios-making-our-app
just modify you codes from these
char *tmp = sqlite3_column_text(selstatement,1);
if (tmp == NULL)
CustomerIdField = nil;
else
CustomerIdField = [[NSString alloc] initWithUTF8String:tmp];
CustomerIdField = [[NSString alloc] initWithUTF8String:
(const char *) sqlite3_column_text(selstatement,1)];
NSLog(#"inside customer is %#",CustomerIdField);
to
int tmp = sqlite3_column_int(selstatement,0);// my case it is int
char *nameChars = (char *) sqlite3_column_text(selstatement, 1);// here is the change occuring please refer this
NSString *name = [[NSString alloc] initWithUTF8String:nameChars]; // there are two steps first fetch as char, then change to String
NSLog(#"customerid is %d",tmp);
NSLog(#"customer name is %#",name);
Try this, It worked for me..
I think the problem is that you are fetching the coustomerId as String directly
In you case just try this
char *custId = (char *) sqlite3_column_text(selstatement, 0);
NSString *customerId = [[NSString alloc] initWithUTF8String:custId];
:-)