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c++qtsqliteqsqlqueryqsqldatabase

How to lock a table in a database via Qt?

I have connected to a database in Qt using c++.

 QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");
 db.setDatabaseName("/link/to/my.db");

Simultaneously I have a Python program that connect to same database and constantly updates a table called "myTable".

From Qt I want to read the newly updated rows each time I poll. So I want to

Lock the table; Read all rows; Delete all the rows; Unlock the Table.

How do I lock and Unlock the table in Qt

Solution

  • There is no lock command for tables in SQLite. But you can lock the database by transaction :

    BEGIN IMMEDIATE TRANSACTION;
...
COMMIT TRANSACTION;

    Or

    BEGIN EXCLUSIVE TRANSACTION;
...
COMMIT TRANSACTION;

    So you can execute transactions commands before and after your operations :

    q.exec("BEGIN IMMEDIATE  TRANSACTION");

...

q.exec("COMMIT");

    Or

     db.transaction(); // Begins a transaction

 ...

 db.commit(); //Commits a transaction