internal ModelQuery(IDataProvider dataProvider, ModelQueryProvider queryProvider, Expression expression)
 {
     _dataProvider = dataProvider;
     Expression    = expression;
     Provider      = queryProvider;
 }
 internal ModelQuery(IDataProvider dataProvider, AppDataContext appDataContext)
 {
     _dataProvider = dataProvider;
     Expression    = Expression.Constant(this);
     Provider      = new ModelQueryProvider(dataProvider, appDataContext, ElementType);
 }