How to Show Distinct Value From Sqllite Table in iOS? - ios

Question

i am Newbie in iOS Development, and First time Use Sqllite database so Sorry For this Question but i am So Confusing Please Give me Solution for this.
I added Data in to My Sqllite Table Like as
-(void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
sqlite3_stmt *statement;
const char *dbpath = [_databasePath UTF8String];
if (sqlite3_open(dbpath, &_myDatabase) == SQLITE_OK) {
NSString *insertSQL = [NSString stringWithFormat:
#"INSERT INTO ALLREADTABLE (PostId, PostTitle, ImageLink, ShortDescription,Category,PostDate) VALUES (\"%#\", \"%#\", \"%#\", \"%#\",\"%#\",\"%#\")",
post_id, cell.headLabel.text, image,self.shortDiscription,cell.categoryLabel.text,cell.timeLabel.text];
const char *insert_stmt = [insertSQL UTF8String];
sqlite3_prepare_v2(_myDatabase, insert_stmt,
-1, &statement, NULL);
if (sqlite3_step(statement) == SQLITE_DONE)
{
NSString *string=[NSString stringWithFormat:#"Value Added %# %# %# %# %# %#",post_id, cell.headLabel.text, image,self.shortDiscription,cell.categoryLabel.text,cell.timeLabel.text];
NSLog(#"String %#",string);
} else
{
NSLog(#"Failed to add contact");
}
sqlite3_finalize(statement);
sqlite3_close(_myDatabase);
}
Then it is added data in to Data Base as I want and it also added Duplicate Value in to table , so For Distinct Value i Write a Code to Fetch data like as
- (void)getTextFomDB
{
NSString *docsDir;
NSArray *dirPaths;
// Get the documents directory
dirPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
docsDir = dirPaths[0];
// Build the path to the database file
_databasePath = [[NSString alloc]
initWithString: [docsDir stringByAppendingPathComponent:
#"sampleDatabase.db"]];
const char *dbpath = [_databasePath UTF8String];
sqlite3_stmt *statement;
if (sqlite3_open(dbpath, &_myDatabase) == SQLITE_OK)
{
NSString *querySQL = #"SELECT DISTINCT PostId, PostTitle, ImageLink, ShortDescription,Category,PostDate FROM ALLREADTABLE";
const char *query_stmt = [querySQL UTF8String];
if (sqlite3_prepare_v2(_myDatabase, query_stmt, -1, &statement, NULL) == SQLITE_OK)
{
[self.postId removeAllObjects];
[self.postTitle removeAllObjects];
[self.imageLink removeAllObjects];
[self.shortDecsription removeAllObjects];
[self.category removeAllObjects];
[self.postDate removeAllObjects];
while (sqlite3_step(statement) == SQLITE_ROW) {
//NSString *personID = [[NSString alloc] initWithUTF8String: (const char *) sqlite3_column_text(statement, 0)];
NSString *postId = [[NSString alloc] initWithUTF8String: (const char *) sqlite3_column_text(statement, 1)];
NSString *postTitle = [[NSString alloc] initWithUTF8String: (const char *) sqlite3_column_text(statement, 2)];
NSString *ImageLink = [[NSString alloc] initWithUTF8String: (const char *) sqlite3_column_text(statement, 3)];
NSString *shortDescrip = [[NSString alloc] initWithUTF8String: (const char *) sqlite3_column_text(statement, 4)];
NSString *Category = [[NSString alloc] initWithUTF8String: (const char *) sqlite3_column_text(statement, 5)];
NSString *postDate = [[NSString alloc] initWithUTF8String: (const char *) sqlite3_column_text(statement, 6)];
[self.postId addObject:[NSString stringWithFormat:#"%# ", postId]];
[self.postTitle addObject:[NSString stringWithFormat:#"%# ",postTitle]];
[self.imageLink addObject:[NSString stringWithFormat:#"%#",ImageLink]];
[self.shortDecsription addObject:[NSString stringWithFormat:#" %#",shortDescrip]];
[self.category addObject:[NSString stringWithFormat:#" %#",Category]];
[self.postDate addObject:[NSString stringWithFormat:#" %#",postDate]];
}
sqlite3_finalize(statement);
}
sqlite3_close(_myDatabase);
}
}
Then it Give me Error like as
[NSPlaceholderString initWithUTF8String:]: NULL cString
Here I want Distinct Value From My SqlliteTable. please Give me Solution For that. I know It is easy But i am Newbie in Database so please Sorry
and Thanks in advance.

Answer 1

You are using initWithUTF8String to get values from database, So if there is a field in database which accept null data than it will gives you an error when you are trying to fetch null data from database.
I suggest you replace all data retrieving code like
NSString *postId = [[NSString alloc] initWithUTF8String: (const char *) sqlite3_column_text(statement, 1)];
with below code:
NSString *postId = [NSString stringWithUTF8String:(const char *) sqlite3_column_text(statement, 1)];
This will replace not null data to an empty string.

Answer 2

This is being caused by trying to create a NSString object with a NULL string. It is on one of these lines:
[[NSString alloc] initWithUTF8String:(const char *) sqlite3_column_text(statement, ...)];
So, before you create a NSString with the results of the sql statement you need to check for NULL like this:
char *tmp = sqlite3_column_text(statement, 1);
if (tmp == NULL)
postId = nil;
else
postId = [[NSString alloc] initWithUTF8String:tmp];
Reference: lnafziger