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/*
* Copyright (C) 2010-2015 Jeremy Lainé
* Contact: https://github.com/jlaine/qdjango
*
* This file is part of the QDjango Library.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*/
/*! \page queries Making queries
The QDjango object relational mapper (ORM) supports the concept of querysets, borrowed from django's ORM. A queryset is a collection of database objects which match a certain number of user-specified conditions.
You can learn more about querysets by reading the QDjangoQuerySet template class documentation.
\section creating-queries Creating and filtering querysets
Before you can start using querysets, you need to declare your database models as described in \ref models.
The most basic queryset matches all the objects for a given model.
\code
// all users
QDjangoQuerySet<User> users;
\endcode
You can use the QDjangoQuerySet::filter() and QDjangoQuerySet::exclude() methods to add filtering conditions to a querset:
\code
// find all users whose password is "foo" and whose username is not "bar"
QDjangoQuerySet<User> someUsers;
someUsers = users.filter(QDjangoWhere("password", QDjangoWhere::Equals, "foo") &&
QDjangoWhere("username", QDjangoWhere::NotEquals, "bar"));
// find all users whose username is "foo" or "bar"
someUsers = users.filter(QDjangoWhere("username", QDjangoWhere::Equals, "foo") ||
QDjangoWhere("username", QDjangoWhere::Equals, "bar"));
// find all users whose username starts with "f":
someUsers = users.filter(QDjangoWhere("username", QDjangoWhere::StartsWith, "f"));
\endcode
You can also use the QDjangoQuerySet::limit() method to limit the number of returned rows:
\code
// limit number of results
someUsers = users.limit(0, 100);
\endcode
\section iterating-queries Iterating over results
The easiest way to iterate over results is to use Qt's <a href="http://doc.qt.io/qt-5/containers.html#the-foreach-keyword">foreach</a> keyword:
\code
// iterate over matching users
foreach (const User &user, someUsers) {
qDebug() << "found user" << user.username;
}
\endcode
Another way of iterating over results is to run over model instances using the QDjangoQuerySet::size() and QDjangoQuerySet::at() methods:
\code
// iterate over matching users
User user;
for (int i = 0; i < someUsers.size(); ++i) {
if (someUsers.at(i, &user)) {
qDebug() << "found user" << user.username;
}
}
\endcode
It is also possible to retrieve field data without creating model instances using the QDjangoQuerySet::values() and QDjangoQuerySet::valuesList() methods:
\code
// retrieve usernames and passwords for matching users as maps
QList<QVariantMap> propertyMaps = someUsers.values(QStringList() << "username" << "password");
foreach (const QVariantMap &propertyMap, propertyMaps) {
qDebug() << "username" << propertyList["username"];
qDebug() << "password" << propertyList["password"];
}
// retrieve usernames and passwords for matching users as lists
QList<QVariantList> propertyLists = someUsers.valuesList(QStringList() << "username" << "password");
foreach (const QVariantList &propertyList, propertyLists) {
qDebug() << "username" << propertyList[0];
qDebug() << "password" << propertyList[1];
}
\endcode
\section other-queries Other operations
\code
// count matching users without retrieving their data
int numberOfUsers = someUsers.count();
// delete all the users in the queryset
someUsers.remove();
\endcode
*/
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