Here is my second stupid Noob problem. I am trying to do a simple Delete and I keep blowing up on the prepare step. I already have other Deletes, Inserts, Updates and Selects working. I am sure it is something simple. I appreciate your help.
+ (void)flushTodaysWorkouts {
sqlite3_stmt *statement = nil;
//open the database
if (sqlite3_open([[BIUtility getDBPath] UTF8String], &database) != SQLITE_OK) {
sqlite3_close(database);
NSAssert(0, #"Failed to opendatabase");
}
NSArray *woList = [self todaysScheduledWorkouts];
for (Workout *wo in woList) {
NSInteger woID = wo.woInstanceID;
if(statement == nil) {
const char *sql = "DELETE FROM IWORKOUT WHERE WOINSTANCEID = ?";
if(sqlite3_prepare_v2(database, sql, -1, &statement, NULL) != SQLITE_OK)
NSAssert1(0, #"Error while creating delete statement. '%s'", sqlite3_errmsg(database));
}
//When binding parameters, index starts from 1 and not zero.
sqlite3_bind_int(statement, 1, woID);
if (SQLITE_DONE != sqlite3_step(statement))
NSAssert1(0, #"Error while deleting. '%s'", sqlite3_errmsg(database));
sqlite3_finalize(statement);
}
if(database) sqlite3_close(database);
}
I solved this, but I don't know why. It did not want to let me do the deletes inside of the for loop. I put the delete in it's own method and called it from a for loop and it worked great. Weird.
I have just come across this error message, and it turned out to be two threads executing queries simultaneously. Just rearranging the code was enough to change the timing so that it would go away.
Adding locks to prevent multiple accesses to the database resolved the problem
I've just encountered a similar one.
It turned out I forgot to reset a prepared and bound statement for DELETE, which would run into trouble the second time it got invoked.
For the case in this question, perhaps the sqlite3_finalize should be replaced with a splite3_reset to reuse in a loop block. And the statement should be finalized only after the loop before invoking sqlite3_close.
Related
So basically I have an app that will provide tasks based on selected project. Both projects and tasks are stored in a SQLite database.
To get the current project id I compare the selected project (_selectedProject) to my database, to get the ID. This is done in my getSelectedProjectId method. However, when running this method in the getTasks method, the Where-statement wont work at all. If I don't run the getSelectedProjectId method first, it works just fine. Am I forgetting to release something? Or is it something else? Any ideas?
I'm pretty new to both SQLite and Objective C, so this may not be a complex issue. I have made sure the getSelectedProjectId method returns the correct project ID. I have also made sure the query that is run in the getTasks method is correct, and when running it through my terminal it returns a number of rows. In the app it returns nothing, provided I'm running the getSelectedProjectId somewhere in that method first.
This is the method that fetches the tasks:
- (void)getTasks
{
[self openDB];
sqlite3_stmt *statement;
int projectId = [self getSelectedProjectId];
NSString *query = [NSString stringWithFormat:#"SELECT * FROM tasks WHERE project_id=%i", projectId];
const char *query_statement = [query UTF8String];
sqlite3_prepare_v2(_contactDB, query_statement, -1, &statement, NULL);
while (sqlite3_step(statement) == SQLITE_ROW)
{
// I add the task title to my array of tasks here.
}
sqlite3_finalize(statement);
sqlite3_close(_contactDB);
}
And this is the method that gets the correct project id from the database:
- (int)getSelectedProjectId
{
sqlite3_stmt *statement;
NSString *query = [[NSString alloc]
initWithFormat:#"SELECT id FROM projects WHERE title=\"%#\" LIMIT 0,1",
_selectedProject];
int rowId = 0;
const char *query_statement = [query UTF8String];
[self openDB];
sqlite3_prepare_v2(_contactDB, query_statement, -1, &statement, NULL);
if (sqlite3_step(statement) == SQLITE_ROW)
{
rowId = sqlite3_column_int(statement, 0);
}
sqlite3_finalize(statement);
sqlite3_close(_contactDB);
return rowId;
}
The problem occured because I closed the DB connection in my getSelectedProjectId-method. I'm now leaving my DB open instead, works like a charm.
In my app, I am trying to delete one record from an sqlite db. I use the following code in my DAO to delete. it is working with all other records expect specific one, I can't delete it eventhough the delete statement is executed successfully, I tried every thing but still can't figure out what special about this record (sqlite3_changes return 0 for this record while for others it returns 1 as expected). I am verifying it is not deleted by selecting from the table, I always find it there.
I tried to delete it from command line (sqlite on mac), still I can't delete it. Appreciate the help as I am really desperate here.
sqlite3_stmt *deleteVideoStmt = nil;
const char *sql = "delete from video where videoID = ?";
if(sqlite3_prepare_v2([DBUtil db], sql, -1, &deleteVideoStmt, NULL) != SQLITE_OK)
NSAssert1(0, #"Error while creating delete video statement. '%s'", sqlite3_errmsg([DBUtil db]));
sqlite3_bind_text(deleteVideoStmt, 1, [v.videoId UTF8String], -1, SQLITE_TRANSIENT);
double t = CFAbsoluteTimeGetCurrent();
/*
if (sqlite3_exec([DBUtil db], "BEGIN IMMEDIATE TRANSACTION", NULL, NULL, NULL) != SQLITE_OK) {
NSLog(#"couldn't begin transacton!!! %s",sqlite3_errmsg([DBUtil db]));
}
*/
int result = sqlite3_step(stmt);
if(SQLITE_DONE != result){
NSLog(#"Error while executing video stmt. '%s'", sqlite3_errmsg([DBUtil db]));
sqlite3_finalize(stmt);
return NO;
}else{
NSLog(#"Update stmt executed successfully. in %ld ms",lroundf(((CFAbsoluteTimeGetCurrent()-t)*1000)));
/*
if (sqlite3_exec([DBUtil db], "COMMIT TRANSACTION", NULL, NULL, NULL) != SQLITE_OK) {
NSLog(#"couldn't commit transacton!!! %s",sqlite3_errmsg([DBUtil db]));
}
*/
NSLog(#"number of rows affected = %d", sqlite3_changes([DBUtil db]));
return YES;
}
I am currently developing on Objective-C using sqlite3. The following code seems like a bad memory access.
-(sqlite3_stmt *)PrepareStmt:(NSString *)query
{
//...
const char *query_stmt = [query UTF8String];
sqlite3_stmt *stmt = nil;
int retval = 0;
if ((retval = sqlite3_prepare_v2(db, query_stmt, -1, &stmt, nil)) == SQLITE_OK)
{
return stmt;
}
else
{
//Error handling...
}
}
- (void)SomeFunc
{
NSString *query = #""; //Assume valid SQL statement
sqlite3_stmt *stmt = [self PrepareStmt:query];
//Use stmt, like step, etc.
sqlite3_finalize(stmt);
}
The sqlite3_stmt in PrepareStmt is set to nil and it will be an out parameter from sqlite3_prepare_v2(). The memory should be allocated in that function. Therefore, it should be released by calling sqlite3_finalize().
My question here is that if we return sqlite3_stmt from PrepareStmt(), it should be still valid right? The local pointer in PrepareStmt() is already popped off the stack, but the memory allocated by sqlite3_prepare_v2() should still be valid.
Is this thinking valid? Or do I need to pass in an address of an pointer to PrepareStmt()?
Thank you!
Yes it's valid in this case. But note that sqlite3_finalize() isn't just about releasing memory (i.e. dealloc). It also sends a message to the DB to tell it to drop it's precompiled SQL statement, etc...
I am new to objective-C and iphone apps.
I am accessing SQLite and have 3 rows in my table "coffee". I used the following way to grab sth out from the table, however, only then 2nd and 3rd rows are being pulled out {the 1st row is always missed}. Is that due to the logic in my while loop by checking while sqlite3_step(selectstmt) returns SQLITE_ROW is wrong? Here is the code:
if (sqlite3_open([dbPath UTF8String], &database) == SQLITE_OK) {
const char *sql = "select coffeeID, coffeeName from coffee";
sqlite3_stmt *selectstmt;
NSLog(#"sqlite_prepare_v2 returns: %i", sqlite3_prepare_v2(database, sql, -1, &selectstmt, NULL));
if(sqlite3_prepare_v2(database, sql, -1, &selectstmt, NULL) == SQLITE_OK) {
NSLog(#"sqlite3_step returns: %i", sqlite3_step(selectstmt));
while(sqlite3_step(selectstmt) == SQLITE_ROW) {
NSInteger primaryKey = sqlite3_column_int(selectstmt, 0);
Coffee *coffeeObj = [[Coffee alloc] initWithPrimaryKey:primaryKey];
coffeeObj.coffeeName = [NSString stringWithUTF8String:(char *)sqlite3_column_text(selectstmt, 1)];
NSLog(#"this is the coffee name: %#", coffeeObj.coffeeName);
coffeeObj.isDirty = NO;
[appDelegate.coffeeArray addObject:coffeeObj];
[coffeeObj release];
}
}
}
On the other hand, is there any convenient way for me to check the number of rows returen in a query directly from the C interface of SQLite?
Many thanks.
You could use the query SELECT COUNT(*) FROM coffee to tell you how many rows there are.
And also, save yourself some headaches and use a SQLite wrapper.
Are the 2 sqlite3_step() calls meant to be executed here?
NSLog(#"sqlite3_step returns: %i", sqlite3_step(selectstmt));
while(sqlite3_step(selectstmt) == SQLITE_ROW {
BTW: there a parenthesis missing in the while line. Do not rewrite your code for SO. Copy/Paste it to avoid copying errors (pasting errors are much more rare)
When retrieving objects from an NSMutableArray in cocoa-touch is the below code ok? Should I be allocating([alloc]) new Page objects each time or is just pointing to it alright? Do I need to do anything to the Page *pageObj after, such as set it to nil?
const char *sql = "insert into Page(Book_ID, Page_Num, Page_Text) Values(?, ?, ?)";
for (i = 0; i < ([[self pagesArray] count] - 1); i++) {
if(addStmt == nil) {
if(sqlite3_prepare_v2(database, sql, -1, &addStmt, NULL) != SQLITE_OK) {
NSAssert1(0, #"Error while creating add statement. '%s'", sqlite3_errmsg(database));
}
}
Page *pageObj = [[self pagesArray] objectAtIndex:i];
if(pageObj.isNew) {
sqlite3_bind_int(addStmt, 1, self.book_ID);
sqlite3_bind_int(addStmt, 2, pageObj.page_Number);
sqlite3_bind_text(addStmt, 3, [[pageObj page_Text] UTF8String], -1, SQLITE_TRANSIENT);
if(SQLITE_DONE != sqlite3_step(addStmt)) {
NSAssert1(0, #"Error while inserting data. '%s'", sqlite3_errmsg(database));
}
NSLog(#"Inserted Page: %i into DB. Page text: %#", pageObj.page_Number, pageObj.page_Text);
}
//Reset the add statement.
sqlite3_reset(addStmt);
}
Thanks. I also understand this should probably be in a transaction but I didn't quite get that working just yet.
The way you're declaring a pointer is correct. You don't need alloc, since that creates a new object, when you want to refer to an existing object in the array. You would want to retain it if you were going to keep the reference outside of that method, but since you're only using it temporarily it's fine not to.
The actual pointer variable will be destroyed and recreated every trip to the loop, so there's no need to set it to nil. Even if you declared the variable outside the loop, simply assigning it to a new object is fine. The only time you'd set it to nil is when you're releasing the object stored in the pointer (or the object may be released elsewhere). If you didn't set it to nil in that case, the pointer would refer to an invalid memory location after the object is dealloced, usually causing a crash.
One bug I can see though, you're skipping the last element in your array in your for loop by subtracting 1 from the count.
Aside from the previously mentioned count error, it looks good.
As far as transactions go, I highly recommend wrapping this write loop in one. It will greatly increase your write performance and I found that it helps with memory usage as well. I use the following class method to begin a transaction:
+ (BOOL)beginTransactionWithDatabase:(sqlite3 *)database;
{
const char *sql1 = "BEGIN EXCLUSIVE TRANSACTION";
sqlite3_stmt *begin_statement;
if (sqlite3_prepare_v2(database, sql1, -1, &begin_statement, NULL) != SQLITE_OK)
{
return NO;
}
if (sqlite3_step(begin_statement) != SQLITE_DONE)
{
return NO;
}
sqlite3_finalize(begin_statement);
return YES;
}
and this one to end a transaction:
+ (BOOL)endTransactionWithDatabase:(sqlite3 *)database;
{
const char *sql2 = "COMMIT TRANSACTION";
sqlite3_stmt *commit_statement;
if (sqlite3_prepare_v2(database, sql2, -1, &commit_statement, NULL) != SQLITE_OK)
{
return NO;
}
if (sqlite3_step(commit_statement) != SQLITE_DONE)
{
return NO;
}
sqlite3_finalize(commit_statement);
return YES;
}
I should probably store the SQL statements for later reuse, but these transaction statements are called much less frequently than my other queries.
Of course not. You have allocated it before and are just referencing the same object. No need to reallocate. Also you don't need to set it to nil.