Wt

I have a database object with an optional many-to-one relationship with another database object. When I fail to provide an object on the one-side of the relationship, I get an error from Wt:

Wt: error during event handling: Wt::Dbo::ptr<Bar>: null dereference
Wt: fatal error: Wt::Dbo::ptr<Bar>: null dereference

My one-side database object looks like this:

class Foo final : public Wt::Dbo::Dbo<Foo> {
public:

  template<typename TAction>
  void persist(TAction& action)
  {
    Wt::Dbo::belongsTo(action, bar_, "Bar");
  }

private:

  Wt::Dbo::ptr<Bar> bar_;
};

And the many-side database object looks like this:

class Bar final : public Wt::Dbo::Dbo<Bar> {
public:

  template<typename TAction>
  void persist(TAction& action)
  {
    Wt::Dbo::hasMany(
      action, foos_, Wt::Dbo::ManyToOne, "Bar");
  }

private:

  Wt::Dbo::collection<Wt::Dbo::ptr<Foo>> foos_;
};

How can I get this to work if I want to make bar_ optional in the one-side Foo objects?

The schema shows that the Bar_id column in the Foo table is nullable, but there is a foreign key constraint on that column. Is that stopping this?

Is there another way to accomplish this?