Filter relation column options - QSqlRelationalDelegate? constrain or restrict option

[talkfig]

qt4.8

I have a relational table model, with editable relations that work.

The table is filtered, and the default relational delegate
collects all possible values from the database as combo options.

I would like to restrict the available options to either:

a) the option set defined by the table's filter - i.e. what's available in the current table
OR
b) manually-generated list (of relations in the current table )

either one will do.

I attempted a specialized createEditor function to
create an editor with a fixed/generated set of options.



QWidget *TeamSelectDelegate::createEditor(QWidget *parent,
const QStyleOptionViewItem & option,
const QModelIndex & index) const
{
Q_UNUSED(option);
const QSqlRelationalTableModel *sqlModel = qobject_cast<const QSqlRelationalTableModel *>(index.model());
QSqlTableModel *childModel = sqlModel ? sqlModel->relationModel(index.column()) : 0;
if (!childModel)
return QItemDelegate::createEditor(parent, option, index);

QComboBox *combo = new QComboBox(parent);
combo->setDuplicatesEnabled(false);
combo->setModel(childModel);
combo->setModelColumn(childModel->fieldIndex(sqlModel->relation(index.column()).displayColumn()));

combo->clear(); // get rid of stuff from model,
combo->addItems(*_relevant_teams); // and put in options from a subset ( generated list )

combo->installEventFilter(const_cast<TeamSelectDelegate *>(this));
return combo;


"_relevant_teams" is a previously generated list of options.
This did not work... it seemed to delete all items in the DB!

Thanks for sharing your ideas.


Cheers!
mike

[talkfig]

Looks like no easy way to accomplish this -
due to a lack of forethought perhaps.

There is a function to get the model of the relations (to setup a filter) but,
the "get" function itself triggers the SQL query to populate the model!

So, my approach is to modify the sql/model/qsqlrelational bits to allow
passing a filter string when setting up the relation like:



Game::m_tmodel->setRelation(3, QSqlRelation("team", "id", "name", "division_id=3"));


Down the "populate()" function chain, a function actually looks for a WHERE condition but no way to setup conditions before the query happens.

now, compiling the Qt sources...

[talkfig]

Tweaking Qt sql-model code got desired results -



diff -r ../../../QtSDK-orig/QtSources/4.8.1/src/sql/models/qsqlrelationaltablemodel.cpp ./src/sql/models/qsqlrelationaltablemodel.cpp
241a242
> setFilter(relation->rel.where()); // This seems to work...
diff -r ../../../QtSDK-orig/QtSources/4.8.1/src/sql/models/qsqlrelationaltablemodel.h ./src/sql/models/qsqlrelationaltablemodel.h
58,59c58,59
< const QString &displayCol)
< : tName(aTableName), iColumn(indexCol), dColumn(displayCol) {}
---
> const QString &displayCol, const QString &where = QString())
> : tName(aTableName), iColumn(indexCol), dColumn(displayCol), _where(where) {}
65a66,67
> inline QString where() const
> { return _where; }
69c71
< QString tName, iColumn, dColumn;
---
> QString tName, iColumn, dColumn, _where;


This allows specifying your WHERE clause to limit the association options for model relations - no special delegate is required.



Game::m_tmodel->setRelation(4, QSqlRelation("team", "id", "name", "team.division_id IN (1,10,11,12)" ));