how to set/read QSqlRelationalTableModel column properties and constraints?

Question

Is there any way to check properties and constraints for each column in a QSqlRelationalTableModel? For example, I'd like to ask my QSqlRelationalTableModel object whether a certain column can contain nulls, or what datatype is valid for that column.

Answer 1

You'll need to get a QSqlField value for each column of the model, which is given by

QSqlRecord record = model->database().record(model->tableName());
QSqlField field = record.field(columnIndex);

then you'll be able to check if a field can be null with QSqlField::requiredStatus() (if the driver supports querying that property) and to get its data type with QSqlField::type().

Answer 2

From alexisdm's answer above, I wrote this simple code snippet to output the properties of each field in a table. Posting it here to save typing for anyone else who is interested.

I also discovered a gotcha: if you use table_model::record() or table_model::record(int) you get unexpected (to me) results for some properties, e.g., isAutoValue seems to always return false, even for fields designated as autoincrement fields in the database. However, you do get a real value for typeID() (though I haven't been able to determine what typeID() is), whereas typeID() always returned -1 for me using model->database().record(model->tableName()).

  QSqlRecord record = table_model->database().record(table_model->tableName());
  // the following get isAutoValue() wrong; but have a real typeID()
  //QSqlRecord record = table_model->record();  
  //QSqlRecord record = table_model->record(table_model->rowCount() - 1);
  qDebug() << "********** table" << table_model->tableName() << "*********";
  for (int i = 0; i < table_model->columnCount(); ++i) {
    QSqlField field = record.field(i);
    qDebug() << "---------- field" << i << field.name() << "--------";
    qDebug() << "default value" << field.defaultValue();
    qDebug() << "is auto value" << field.isAutoValue();
    qDebug() << "is generated" << field.isGenerated();
    qDebug() << "is null" << field.isNull();
    qDebug() << "is read only" << field.isReadOnly();
    qDebug() << "is valid" << field.isValid();
    qDebug() << "length" << field.length();
    qDebug() << "precision" << field.precision();
    qDebug() << "required status" << field.requiredStatus();
    qDebug() << "type" << field.type();
    qDebug() << "type id" << field.typeID();
    qDebug() << "value" << field.value();
  }