The datasource for ComboBox object does not support lambda expressions like ListView (and many other objects). These 'hardcoded' strings are error prone and is causing headaches when altering modelschema's.

DataSource(ds =>
    {
        ds.Custom()
        .Sort(sort => sort.Add("PropertyName").Descending())
        .Transport(tr => 
            tr.Read(read => read.Action("Action", "Controller"}))
        );
    })