Async SQL

The asynchronous version of QSqlTableModel.

I'm sure you love QSqlTableModel as much as I do. The only problem with it is that it's synchronous (which means that all queries run on the UI thread). This makes them unusable for large data sets or complex database queries or slow database access over a network (because it would cause your UI to freeze occasionally).

The solution? Combine the ease of using QSqlTableModel with a powerful single-thread backend. It's basically QSqlTableModel on steroids!

I conceived the concept of this project after reading this article about a year ago. Thanks Dave Berton!

NOTE: I will make this article sound a lot more professional later. Let me have my fun for now!

Features

Works for the SQLite and MySQL databases (only)
Allows for limit setting
Can be used to display tables that requires foreign key (it's still pretty difficult for now, but I've done it before)
Every other feature that the QSqlTableModel has
Allows for custom operations on the database thread (see example below)

How to use

The project itself is an example of how to use this library. However, here's a preview:

// In header file
AsyncSql::AsyncSqlTableModel *model;
...

// In source file
using namespace AsyncSql;
...
// Set database connection options using the DatabaseConnection class
DatabaseConnection::setDefaultDriver(DatabaseConnection::SQLite);
...
model = new AsyncSqlTableModel(this);
model->setTable("sales");

// Using C++11
connect(model, &AsyncSqlTableModel::selected, [this](bool successful)
{
    // Display the first record if successful.
    if(successful)
        qDebug() << "Hello AsyncSql!" << model->record(0);
    else
        qDebug() << "Error discovered: " << model->lastError().text();
});

You can view the table with a QTableView, since AsyncTableModel inherits QAbstractTableModel.

// In header file...
QTableView *view;

// In source file...
view = new QTableView(this);
view->setModel(model);

Custom operations

In some occasions, you may want to run specific commands that are not provided by this library. A good example would be creating a user on a MySQL database. To achieve this, use the AsyncSql::QueryRequest::setCustomOperation() function.

// Assume user name and password are defined
// using namespace AsyncSql;
QueryRequest request(this, "" /*no query*/, tableName(), QueryRequest::CustomOperation);

// Using C++11 ...
request.setCustomOperation([userName, password](QSqlDatabase db)
{
    // db is the connection object used on the query thread
    QSqlQuery qry(db);
    
    // Create user and grant access to database on localhost only
    qry.prepare(QString("CREATE USER '%1'@'localhost' IDENTIFIED BY '%2'").arg(userName, password));
    
    // If query fails, throw an exception that would be caught by the thread
    if(!qry.exec())
        throw DatabaseException(qry.lastError(), tr("Failed to create user %1 on localhost.").arg(userName));
       
    // More commands...
}

emit execute(request);

// Connect to the AsyncSql::AsyncSqlTableModel::executed() signal to check if operation was performed successfully.

The functions AsyncSql::QueryRequest::runBefore() and AsyncSql::QueryRequest::runAfter() are also provided to conveniently run commands before or after a query respectively.

Dependencies

Qt 5 framework

Todo

Database transaction handling
More examples (especially one that uses QML)
Other databases

Lastly, as I always say:

Please report all bugs. Also, I am FAR FROM perfect. If you see anything that can be done better, please notify me.

License

MIT

obeezzy / AsyncSql