C# linq 和表达式

Question

I am new to c# and I am having problem understanding the given problem statement. Problem statement : Write a program to find the vehicles released between certain year.

1. class Vehicle is already given for your reference.

2. class Program contains a hard-coded list with vehicle information in the 'vehicleList' attribute.

a) Implement method 'getVehicleName'.

public static void getVehicleName(int fromYear, int toYear) //method signature

This method must must display the vehicle names (from the given list) released between the fromYear and toYear (including these years). USING LINQ CONCEPT

b) Implement method 'Main'.

Get the from year and to year from the user. Pass it to 'getVehicleName' method.

NOTE : NEED NOT call 'getMyExpression' method in Main.

c) Implement method 'getMyExpression'

public static Expression getMyExpression(int fromYear, int toYear)

This method snippet is already given for you. THIS METHOD IS FOR TESTING YOUR LINQ QUERY EXPRESSION OR LINQ METHOD EXTENSION. So fill your query expression or method extension in the space holder provided. ONLY THE QUERY EXPRESSION OR METHOD EXTENSION. Nothing more need to be implemented in this class.

Answer 1

It seems you're almost there:

from v in vehicle 
where v.ReleaseYear >= fromYear && v.ReleaseYear <= toYear 
select v.VehicleName

alternatively do the same with method chain

vehicle.Where(v => v.ReleaseYear >= fromYear && v.ReleaseYear <= toYear)
.Select(n => n.VehicleName)

Answer 2

也许继承 List 实现方法getVehicleName作为 linq 查询

public string getVehicleName => this.FirstOrDefault(o => ...

Answer 3

from v in vehicleList where v.ReleaseYear>=fromYear &&v.ReleaseYear<=toYear select n;

Answer 4

While implementing getVehicleName use:

from v in vehicleList where v.ReleaseYear>=fromYear && v.ReleaseYear<=toYear 
select v.VehicleName;

And for method extension use:

vehicleList.Where(s=> s.ReleaseYear>=fromyear && s.ReleaseYear<=toYear).ToList()

Answer 5

Vehicle.cs

public class Vehicle          
{
    public String VehicleId{get; set; }
    public String VehicleName{ get; set; }
    public String Brand { get; set; }
    public int ReleaseYear { get; set; }

    public Vehicle(String vehicleId, String vehicleName, String brand,int releaseYear)
    {
        this.VehicleId = vehicleId;
        this.VehicleName = vehicleName;
        this.Brand = brand;
        this.ReleaseYear = releaseYear;
    }
    
}

Program.cs

    static void Main(string[] args)   
    {
        
        
        Console.WriteLine("Enter From Year :");
        int fromYear = int.Parse(Console.ReadLine());
        Console.WriteLine("Enter To Year :");
        int toYear = int.Parse(Console.ReadLine());
        GetVehicleName(fromYear,toYear);
     
        
        
    }
    public static void GetVehicleName(int fromYear , int toYear){
        var resultQuery = from v in VehicleList where v.ReleaseYear >= fromYear && v.ReleaseYear <= toYear orderby v.ReleaseYear select v;
        Console.WriteLine($"Vehicle Name Released Between {fromYear} And {toYear} :");
        foreach (Vehicle s in resultQuery)
        {
            Console.WriteLine(s.VehicleName);

        }
        Console.ReadKey();
        
        
    }
    public static ParameterExpression variableExpr = Expression.Variable(typeof(IEnumerable<Vehicle>), "sampleVar");
    
    public static Expression GetMyExpression(int fromYear, int toYear)
    {  
        
        Expression assignExpr = Expression.Assign(variableExpr, Expression.Constant(from v in VehicleList where v.ReleaseYear >= fromYear && v.ReleaseYear <= toYear orderby v.ReleaseYear select v));
        return assignExpr;
    }