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.
Creating and filtering querysets
Before you can start using querysets, you need to declare your database models as described in Database models.
The most basic queryset matches all the objects for a given model.
The QDjangoQuerySet class is a template class for performing database queries.
Definition: QDjangoQuerySet.h:47
You can use the QDjangoQuerySet::filter() and QDjangoQuerySet::exclude() methods to add filtering conditions to a querset:
QDjangoQuerySet filter(const QDjangoWhere &where) const
Definition: QDjangoQuerySet.h:483
The QDjangoWhere class expresses an SQL constraint.
Definition: QDjangoWhere.h:41
@ StartsWith
Returns true if the column value starts with the given value (strings only).
Definition: QDjangoWhere.h:52
@ NotEquals
Returns true if the column value is not equal to the given value.
Definition: QDjangoWhere.h:47
@ Equals
Returns true if the column value is equal to the given value.
Definition: QDjangoWhere.h:46
You can also use the QDjangoQuerySet::limit() method to limit the number of returned rows:
someUsers = users.
limit(0, 100);
QDjangoQuerySet limit(int pos, int length=-1) const
Definition: QDjangoQuerySet.h:521
Iterating over results
The easiest way to iterate over results is to use Qt's foreach keyword:
foreach (const User &user, someUsers) {
qDebug() << "found user" << user.username;
}
Another way of iterating over results is to run over model instances using the QDjangoQuerySet::size() and QDjangoQuerySet::at() methods:
User user;
for (
int i = 0; i < someUsers.
size(); ++i) {
if (someUsers.
at(i, &user)) {
qDebug() << "found user" << user.username;
}
}
T * at(int index, T *target=0)
Definition: QDjangoQuerySet.h:364
int size()
Definition: QDjangoQuerySet.h:596
It is also possible to retrieve field data without creating model instances using the QDjangoQuerySet::values() and QDjangoQuerySet::valuesList() methods:
QList<QVariantMap> propertyMaps = someUsers.
values(QStringList() <<
"username" <<
"password");
foreach (const QVariantMap &propertyMap, propertyMaps) {
qDebug() << "username" << propertyList["username"];
qDebug() << "password" << propertyList["password"];
}
QList<QVariantList> propertyLists = someUsers.
valuesList(QStringList() <<
"username" <<
"password");
foreach (const QVariantList &propertyList, propertyLists) {
qDebug() << "username" << propertyList[0];
qDebug() << "password" << propertyList[1];
}
QList< QVariantList > valuesList(const QStringList &fields=QStringList())
Definition: QDjangoQuerySet.h:630
QList< QVariantMap > values(const QStringList &fields=QStringList())
Definition: QDjangoQuerySet.h:618
Other operations
int numberOfUsers = someUsers.
count();
int count() const
Definition: QDjangoQuerySet.h:442
bool remove()
Definition: QDjangoQuerySet.h:572