In my app in QT5 I have this code
QString sql = "Select * from table";
QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");
db.setDatabaseName("./au.sqlite");
db.open();
QSqlQuery query(sql);
query.exec();
But when I get the results only get one result, the select query only give me one result and I don't know how fix this. If I add query.next() in a while loop I only get one iteration.
There is a bool function that returns true if the query succeeded. Looking back to the docs:
Successfully executed SQL statements set the query's state to active so that isActive() returns true. Otherwise the query's state is set to inactive.
This is the way you can check the result. If it's false, then You should try to rewrite your sql query text so that functional sql words (such as SELECT, FROM and etc.) are in the upper case (the way it's shown in the docs) and try to execute the query once again.
Here's an example from the docs again:
QSqlQuery query("SELECT country FROM artist");
while (query.next()) {
QString country = query.value(0).toString();
doSomething(country);
}
You might check sqlbrowser example that is included with Qt5 distribution. Run your query there on your db.
Related
This is my first post in stack-overflow, so sorry in advance for possible "bad practices".
Context: the goal is to send SPARQL queries through http-requests to a GraphDB data base.
Problem: to construct the queries on code in a safe way. Currently done by means of std::string dummyStr = "Hello"+" World" or dummyStr.append("bla") (I was told this was not safe due to XSS, but thats not the issue here)
Question: do you know any query builder library for doing this string concatenation?
A search for C++ query builder on the web returned this answer.
After implementing the approach with the suggested Qt QSqlQuery class, I'm able to ".prepare" the query, but not to ".bindValue".
QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");
db.open();
QSqlQuery startQuery;
/*Prepare query*/
startQuery.prepare("INSERT INTO person (id, forename, surname) "
"VALUES (:id, :forename, :surname)");
startQuery.bindValue(":id", 1001);
startQuery.bindValue(":forename", "Bart");
startQuery.bindValue(":surname", "Simpson");
/*convert query to std::string*/
QString startQueryString = startQuery.lastQuery();
std::string dummyQuery = startQueryString.toUtf8().constData();
Why can't I bind the values to the placeholders?
Is it because I have no "actual" database, but rather a dummy-database just to construct the query?
My actual Query looks something like this:
SELECT ?s WHERE { FILTER(STRSTARTS(STR(?s),":referenceIRI")). ?s rdf:type rdfs:Class.}
And I would like to treat :referenceIRI as a placeholder.
I've searched overall to try to overcome this problem, as I just need the query-builder functionality.
Also: on my actual SPARQL query I have both ? and :myVal elements, which are the 2 types of placeholders in QSqlQuery for binding values. Any idea on how to by-pass the ? placeholder and just consider the :myVal-type?
I am trying to fetch some records from MySQL database by using a prepared statement by using QSqlQuery as:
QString username=ui->textEdit_password->toPlainText();
QString password=ui->textEdit_password->toPlainText();
QSqlQuery query;
query.prepare("SELECT * FROM login_access WHERE username=? AND password=?");
query.addBindValue(username);
query.addBindValue(password);
query.exec();`
When i run :
std::string q_str1=query.executedQuery().toUtf8().constData();
std::cout<<"Query : "<<q_str1<<"\n";
It outputs : Query : SELECT * FROM login_access WHERE username=? AND password=? where the "?" has not been replaced and the query returns nothing since the "?" character is compared to the database records.
On running the query: SELECT * FROM login_access, the query returns all the database records in the login_access table.
I have also tried replacing the "?" with placeholders ":uname",":pass" and changed query.addBindValue(username); to query.bindValue(":uname",username);, and done same with password field.
I am running QtCreator 4.4.1
Thanks.
Use query.bindValue( ...) because this sets the placeholder value.
I tested executedQuery() on one of my SQL statements with placeholders and it returned a string with just the placeholders, not the values. The documentation does say that in most cases it the same string as lastQuery().
http://doc.qt.io/qt-5/qsqlquery.html#executedQuery
You have confirmed that your SQL statement without the where clause works so the next stage is to check you are binding what you think you are binding. To do this use boundValue(const QString placeholder) to find out if the placehold value is being bound.
It might also be useful to check the query has run OK.
So, after your query.exec you should put the following (assuming these are your placeholders) just to check these things:
qDebug() << query.lasterError();
qDebug() << query.boundValue(":uname");
qDebug() << query.boundValue(":pass");
I know many questions were asked around the issue I have, I spent along time trying to implement all kinds of solutions but didn't help.
I am trying to read a .db file using Qt SQLite platform.
windows 8 Qt 5.3.2
Opening the db file in DB browser for SQLite and executing my simple query succeeds:
SELECT Name FROM Person ORDER BY Name
and there is a list of 10 rows at the output.
I would like to do it throw Qt. my code:
QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");
db.setDatabaseName("C:\mydb.db");
if(db.open())
{
QSqlQuery qry(db);
if(qry.exec("SELECT Name FROM Person ORDER BY Name"))
{
while(qry.next())
{
//some code
}
}
QSqlError e;
QString s,d;
e = qry.lastError();
s = e.databaseText();
d = e.driverText();
}
this code falls, the qry.exec command returns false, and last error is "no such table; person"
Running the command: QStringList tables = db.tables(QSql::AllTables);
after the Data Base is open shows that there is one table in Data Base called: sqlite_master.
trying to replace the query within the exec command with the query: "SELECT tbl_name FROM sqlite_master WHERE type = 'table'"
as says at: http://www.sqlite.org/faq.html#q7
causes the exec command to return true but qry.next() returns false already from the first iteration, although I have 5 tables in my data base.
I would be great full to how ever can me with my problem!
thanks!!!
You should specify the path to the database file correctly. Instead of C:\mydb.db you should use C:\\mydb.db or C:/mydb.db.
That's because the compiler uses \ as an escape character in strings (for things like \t, \n or \r). so \\ is actually turned into \.
I have written a QT GUI application that connects to an Oracle Database and performs query and shows the output in a QTableView.
QString host_name=ui->lineHostName->text();
QString db_name=ui->lineDatabaseName->text();
QString user_name=ui->lineUserName->text();
QString pass_word=ui->linePassword->text();
QString port_no=ui->linePortNumber->text();
QSqlDatabase db = QSqlDatabase::addDatabase("QOCI");
db.setHostName(host_name);
db.setDatabaseName(db_name);
db.setUserName(user_name);
db.setPassword(pass_word);
db.setPort(port_no.toInt());
QString MyQuery = ui->lineQuery->text();
db.open();
QSqlQuery query(MyQuery,db);
if(query.exec())
{
this->model=new QSqlQueryModel();
model->setQuery(MyQuery);
ui->tableViewOra->setModel(model);
}
After running the program, I tried to use this (as a substitute of the DESC )---
SELECT
column_name "Name",
nullable "Null?",
concat(concat(concat(data_type,'('),data_length),')') "Type"
FROM user_tab_columns
WHERE table_name='my_table_number_one';
And the column names, null parameter and data type was shown on the QTableView
Now my question is, can I use this information in the QTableView to create another table with same Column names and data type ??? (Basically creating a copy of my queried table table).
EDIT
After suggestions i tried modifying with---
QString query_to_replicate;
query_to_replicate=QString("CREATE OR REPLACE TABLE %1 AS %2").arg("AJ_REPLACEMENT_TESTING").arg(ui->lineEdit->text());
QSqlQuery query_second(query_to_replicate,db);
if(query_second.exec())
{
ui->r_pop_Button->setStyleSheet("QPushButton {background-color: rgb(0, 255, 0);}");
this->model_relocate=new QSqlQueryModel();
model_relocate->setQuery(query_second);
ui->tableView2->setModel(model_relocate);
while (model_relocate->canFetchMore())
model_relocate->fetchMore();
qDebug()<<QDateTime::currentDateTime()<<"Query SUCCESS ";
db.close();
}
now it worked twice, without throwing errors and created replicated copies in the oracle database (I used different names for replicated table before building).
But after running successfully twice, it seized replicating. Situation is completely clueless. I am not getting any errors during build / compile time.
You can do this by using CREATE TABLE AS SELECT:
QString sql = "CREATE TABLE %1 AS %2"
.arg(yourNewTableName)
.arg(ui->lineQuery->text());
// and execute this sql code on your QSqlDatabase as you do it above
It will create new table, with name from "yourNewTableName" variable and copy data from select query to new table.
Code update:
QString query_to_replicate;
query_to_replicate=QString("CREATE OR REPLACE TABLE %1 AS %2").arg("AJ_REPLACEMENT_TESTING").arg(ui->lineEdit->text());
QSqlQuery query_second(query_to_replicate,db); // query will be executed there! weird, but...
if (query_second.lastError().isValid())
{
qDebug() << query_second.lastError().text(); // error happens
}
else
{
qDebug() << "Table created successfully";
}
Also, you must #include <QSqlError> in the top of file, to use QtSql errors.
Im working on a project where im trying to build a QTreeWidget that has multiple QTreeWidgetItems
and once i click on a particular item it connects to a database and shows a query result in a tableview model, until now every thing works fine.
the problem is that i want each item to output different resut depending on some criteria on the same table where this criteria is only changing the value of an attribute, and this value is the same of the item name. for example item named 122 and the table has atribute called no. when we click on item 122 the result of this query must be shown (select * from table where no=122)
any help :)
I am assuming you have a QTableView backed by a QSqlQueryModel or QSqlTableModel.
You can connect to the signal QTreeWidget::itemSelectionChanged() and then in the slot you get the current item with selectedItems()[0]. Then you create your query:
QSqlQuery query;
query.prepare("select * from table where no=:no");
query.bindValue(":no", number);
query.exec();
Finally you can use setQuery (const QSqlQuery & query) on the model. This should update your view.
I hope I understood correctly what you want to achieve.