Question

bool ok = query.exec("CREATE TABLE person ( IdTable INTEGER IDENTITY(1,1) NOT NULL PRIMARY KEY, LastName varchar(255), FirstName varchar(255)  )");            
bool ok1 = query.exec("INSERT INTO person VALUES ('Wijethilake','Tharanga')");            
QSqlQuery scope_Identity("SELECT SCOPE_IDENTITY() AS Current_Identity;");
QSqlRecord rec = scope_Identity.record();
qDebug() << scope_Identity.isValid();

This returns false. IS it that something wrong with qt or is my scope Identity statement wrong. I really appreciate someone’s help on this.

Thank you.

Answer 1

This may be related to how QSqlQuery operates.

I don’t know QSqlQuery, but I have had a similar issue with SCOPE_IDENTITY() in other languages where the INSERT and SELECT SCOPE_IDENTITY()... statements are run in different scopes – meaning that the results of the INSERT are not accessible to SCOPE_IDENTITY() – typically because they are executed as dynamic SQL by the data access layer. You can validate this by running a SQL trace on your database server for SQL:BatchCompleted events.

Assuming this is the issue, you need to execute both statements in the same scope to return the new identity. I’m not sure if this is valid QSqlQuery, but something like

QSqlQuery scope_Identity("INSERT INTO person VALUES ('Wijethilake','Tharanga'); SELECT SCOPE_IDENTITY() AS Current_Identity;");
QSqlRecord rec = scope_Identity.record();
qDebug() << scope_Identity.isValid();

In SQL 2005 and later, an alternative to SCOPE_IDENTITY() is the OUTPUT clause, which enables you to do the whole thing in one statement:

QSqlQuery scope_Identity("INSERT INTO person OUTPUT inserted.IdTable VALUES ('Wijethilake','Tharanga');");
QSqlRecord rec = scope_Identity.record();
qDebug() << scope_Identity.isValid();