QCompleter with SQL

QCompleter is a Qt class that provides autocompletion functionality in user input interactions. It is commonly used in text input fields to suggest possible values based on user input, saving time on manual entry and reducing error rates.

In this tutorial, we will explore how to use QCompleter with SQL (Structured Query Language) to provide autocompletion suggestions from a database.

Requirements

To follow along, you will need:

• Qt
• A database containing the data you want to use for autocompletion

Creating a Database

For this tutorial, we will use a simple database with a single table names that has one column name.

CREATE TABLE names (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    name TEXT NOT NULL
);

You can populate this table with some data to test the QCompleter functionality.

Setting up QCompleter

QCompleter requires a model that provides the data to autocomplete from. We can use QSqlQueryModel to populate the model from the database.

#include <QtWidgets>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    // Create database connection
    QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");
    db.setDatabaseName("test.db");
    if (!db.open()) {
        qDebug() << "Error opening database";
        return 1;
    }

    // Create the model
    QSqlQueryModel *model = new QSqlQueryModel;
    model->setQuery("SELECT name FROM names");

    // Create the completer
    QCompleter *completer = new QCompleter(model);
    completer->setCaseSensitivity(Qt::CaseInsensitive);
    completer->setCompletionMode(QCompleter::PopupCompletion);

    // Create the input box
    QLineEdit *lineEdit = new QLineEdit;
    lineEdit->setCompleter(completer);

    // Create a layout and add the input box
    QVBoxLayout *layout = new QVBoxLayout;
    layout->addWidget(lineEdit);

    // Create a main window, set the layout, and show it
    QWidget *window = new QWidget;
    window->setLayout(layout);
    window->show();

    return a.exec();
}

In this example, we have created a QSqlQueryModel object that queries the database for the names column in the names table. We then create a QCompleter object using this model and set the case sensitivity and completion mode. Finally, we create a QLineEdit object for user input and set the completer to the input box.

Conclusion

Using QCompleter with SQL is a powerful way of integrating autocompletion functionality into your application, allowing users to easily input and select data from a database. With some modifications to the QSqlQueryModel query, you can customize the data to autocomplete from, making it easy to provide suggestions based on your use case.