C#•2mo ago

Why can't I use the null propagation operator in lambda expressions?

using (ProfitCalculatorDataBaseContext db = new ProfitCalculatorDataBaseContext())
{
    var customers = db.Customers.ToList();
    var orders = db.Orders.Where(o => o.OrderStatus != "Готов")
                         .Select(o => new OrdView
                         {
                             oId = o.Id,
                             oData = o.Data,
                             oCustomersMail = customers.FirstOrDefault(c => c.CustomerId == o.CustomerId)?.Mail ?? "Не найдено",
                             oStartPoint = o.StartPoint,
                             oFinalPoint = o.FinalPoint,
                             oTrackNumber = o.TrackNumber,
                             oOrderStatus = o.OrderStatus,
                             oComment = o.Comment,
                             oMoneyPerOrder = o.MoneyPerOrder
                         })
                         .ToList();

    activeOrdersGrid.ItemsSource = orders;
}

using (ProfitCalculatorDataBaseContext db = new ProfitCalculatorDataBaseContext())
{
    var customers = db.Customers.ToList();
    var orders = db.Orders.Where(o => o.OrderStatus != "Готов")
                         .Select(o => new OrdView
                         {
                             oId = o.Id,
                             oData = o.Data,
                             oCustomersMail = customers.FirstOrDefault(c => c.CustomerId == o.CustomerId)?.Mail ?? "Не найдено",
                             oStartPoint = o.StartPoint,
                             oFinalPoint = o.FinalPoint,
                             oTrackNumber = o.TrackNumber,
                             oOrderStatus = o.OrderStatus,
                             oComment = o.Comment,
                             oMoneyPerOrder = o.MoneyPerOrder
                         })
                         .ToList();

    activeOrdersGrid.ItemsSource = orders;
}

8 Replies

Jimmacle•2mo ago

what does the error say?

ApathyErr•2mo ago

CS8072 - An expression tree lambda may not contain a null propagating operator.

Jimmacle•2mo ago

well that's why it's not just a lambda, it's an expression and those don't support a number of things

Jimmacle•2mo ago

https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/compiler-messages/expression-tree-restrictions

Some C# expressions are prohibited in expression trees. Learn which...

These compiler errors and warnings indicate that an expression would include an expression that isn't allowed in an expression tree. You need to refactor your code to remove the prohibited expression.

ApathyErr•2mo ago

How else can I fix it then?

Jimmacle•2mo ago

by refactoring the code so the prohibited expressions aren't in the expression

JakenVeina•2mo ago

oCustomersMail = customers.Any()
    ? customers.First(c => c.CustomerId == o.CustomerId).Mail
    : "Не найдено",

oCustomersMail = customers.Any()
    ? customers.First(c => c.CustomerId == o.CustomerId).Mail
    : "Не найдено",

Unknown User•2mo ago

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Why can't I use the null propagation operator in lambda expressions?