C# Winforms .NET v4.5.2: best approach for bound objects/controls to save & display updated values

Question

I have some objects which are loaded from an SQLite database into a separate list. The user can select an item from that list via combobox and edit its data in a subform. I work with Binding so that the list and its item is immediately updated on every change. Furthermore, I have a LastModified field (DateTime) in order to see the time of the last change which is set via my item SaveToDB() method.

Now, I am wondering how to handle the database update as well as the display of updated bound values correctly and have 3 open questions:

1. How am I able to store the old item values in order to compare those with the final edit (after leaving the edit control, like a TextBox) without reading the database entry again? As all bound variables are immediately changed with the edit I think I would need a copied item object when the object is loaded and saved inbetween but which is not bound itself. How can I create such a copy?

2. What is the best event to fire the comparison and database update? I think it is Validated() but I am not sure. It definitely is not the Changed() event as here a database update would be triggered after every keystroke, even when the changes are undone again before leaving the edit control (for which I want to use the comparison in point 1 to get rid of unnecessary database updates).

3. Why is my bound DateTime label not updated when I call the entity SaveToDB() method? Do you need to rebind every control after each code internal change of object properties? Seriously? I find it also a bit stupid to explicitely update the combobox.Text while the updated data is correctly displayed when I dropdown the combobox. Really strange behaviour.

Code:

public class Entity {
    public int ID { get; set; }
    public string DateTime { get; set; }
    public string Name { get; set; }

    ...

    public void SaveToDB() {
        DateTime = System.DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss");
        if (DB.Read(QueryRead()) == null) {
            DB.Write(QueryAdd());
        } else {
            DB.Write(QueryUpdate());
        }
    }
}

public class Entities : SortableBindingList<Entity> {
    ...
}

public class EntityStore {
    public Entities Entities;
    public BindingSource Source; // used for combobox.datasource in selector-form

    // singleton
    ...

    public EntityStore() {
        Entities = new Entities();
        Source = new BindingSource() { DataSource = Entities };
        ReadAllFromDB(); // fills Entities
    }

    ...

    public void Update(Entity entity) {
        entity.SaveToDB();
    }
}

public partial class FormSelector : Form {
    // FormEntity gets the selected entity via its parent form:
    FormEntity formEntity;
    ...
    cbxEntity.DataSource = EntityStore.Current.Source;
    formEntity.SetEntity(EntityStore.Current.Entities.FirstOrDefault(x => x.ID == ((Entity)((GridViewRowInfo)(cbxEntity.SelectedItem)).DataBoundItem).ID));
    ...
}

public partial class FormEntity : Form {
    Entity entity;

    ...

    public void SetEntity(Entity entity) {
        this.entity = entity;
        tbxID.DataBindings.Add(new Binding("Text", entity, "ID", false));
        lblDateTime.DataBindings.Add(new Binding("Text", entity, "DateTime", false));
        tbxName.DataBindings.Add(new Binding("Text", entity, "Name", false));
    }

    private void tbxName_Validated(object sender, EventArgs e) {
        // missing comparison logic
        // ...

        // I could also directly call entity.SaveToDB(); here but I would like
        // to keep the logic flow separated as follows:
        // DB <- Entity <- EntityStore <- Form(s)
        EntityStore.Current.Update(entity);
    }
}

Sidenote/Question: I also stumbled over the INotifyPropertyChanged event but I do not understand if its used in winforms and for what purpose.

To prevent a stack overflow exception by implementing INotifyPropertyChanged you additionally need to use private properties when getting and setting public properties.