Question

我刚刚发布了这个问题但得到了我的问题的部分答案，所以我想我发布了更多解释，希望得到更准确的答案。我有2个班级：

public class Employee
{
    public string Name { get; set; }
    public List<Cars> Cars { get; set; }
}

public class Car
{
    public int CarID { get; set; }
    public CarTypes CarType { get; set; }
    public enum CarTypes
    {
        Van,
        SmallCar
    }
}

我正在努力只让所有拥有面包车的员工忽略那些使用Lambda的SmallCars，我试过这一行：

List<Employee> EmployeesWithVans = AllEmployees.Where(emps => emps.Car.Any(cartype => cartype.CarType == Car.CarTypes.Van)).ToList();

但如果我尝试（.Any）至少有一辆面包车被分配给员工（.All），这将获得所有员工，如果不是所有员工都拥有Van，它将不会带回任何东西。

是否可以使用嵌套的Lambda实现这一点？

感谢。

编辑：

Employee Mark = new Employee();
Mark.Cars.Add(new Car() { CarType = Car.CarTypes.Van, CarID = 12 });
Mark.Cars.Add(new Car() { CarType = Car.CarTypes.Van, CarID = 13 });
Mark.Cars.Add(new Car() { CarType = Car.CarTypes.SmallCar, CarID = 14 });

Employee Lisa = new Employee();
Lisa.Cars.Add(new Car() { CarType = Car.CarTypes.Van, CarID = 15 });
Lisa.Cars.Add(new Car() { CarType = Car.CarTypes.SmallCar, CarID = 16 });
Lisa.Cars.Add(new Car() { CarType = Car.CarTypes.SmallCar, CarID = 17 });

    List<Employee> EmployeesWithVans should contain:

    Employee FilteredMark contains:
    Mark.Cars.Add(new Car() { CarType = Car.CarTypes.Van, CarID = 12 });
    Mark.Cars.Add(new Car() { CarType = Car.CarTypes.Van, CarID = 13 });

    Employee FilteredLisa contains:
    Mark.Cars.Add(new Car() { CarType = Car.CarTypes.Van, CarID = 15 });

Answer 1

试试这个：

List<Employee> Temp = AllEmployees.Where(emps => emps.Cars.Any(cartype => cartype.CarType == Cars.CarTypes.Van)).ToList();

List<Employee> EmployeesWithVans = (from item in Temp
           select new Employee{ 
                                     Name = item.Name, 
                                     Cars = (item.Cars.Where( car => car.CarType == Cars.CarTypes.Van)).ToList()
                               }).ToList();

这是我试过的（在LINQPAD中）：

void Main()
{
    List<Employee> AllEmployees = new List<Employee>();

    List<Cars> lcars1 = new List<Cars>();
    Cars car1 = new Cars();
    car1.CarType = Cars.CarTypes.Van;
    lcars1.Add(car1);lcars1.Add(car1);

    Cars car2 = new Cars();
    car2.CarType = Cars.CarTypes.SmallCar;
    lcars1.Add(car2);

    List<Cars> lcars2 = new List<Cars>();
    lcars2.Add(car1);lcars2.Add(car2);lcars2.Add(car2);

    AllEmployees.Add(new Employee(){ Name="emp1", Cars = lcars1});
    AllEmployees.Add(new Employee(){ Name="emp2", Cars = lcars2});
    AllEmployees.Add(new Employee(){ Name="emp3", Cars = lcars1 });
    AllEmployees.Add(new Employee(){ Name="emp4", Cars = lcars2});

    List<Employee> Temp = AllEmployees.Where(emps => emps.Cars.Any(cartype => cartype.CarType == Cars.CarTypes.Van)).ToList();

    List<Employee> EmployeesWithVans = (from item in Temp
            select new Employee{ 
                                        Name = item.Name, 
                                        Cars = (item.Cars.Where( car => car.CarType == Cars.CarTypes.Van)).ToList()
                                }).ToList();

    EmployeesWithVans.Dump();
}

输出：

enter image description here

Answer 2

这是你想要的吗？（所有员工至少有一辆面包车，但没有小车）

var EmployeesWithVans = AllEmployees
                        .Where(emps => emps.Cars.Any(cartype => cartype.CarType == Cars.CarTypes.Van)
                                       && !emps.Cars.Any(cartype => cartype.CarType == Cars.CarTypes.SmallCar))
                        .ToList();

Answer 3

查询是正确的，如果为其分配了面包车，它会在返回序列中添加Employee。我不太确定问题出在哪里，你认为你的查询没有任何回报，因为并非所有员工都有货车吗？如果是，这将是Where运算符的实现：

foreach(var elem in input)
{
  if (predicate(elem))
    yield return elem;
}

谓词将应用于序列中的所有元素，如果元素满足它，它将作为序列的一部分返回。

具有嵌套类的Lambda

3 个答案: