Is there a way to use lambda function to get the list?

Question

I have a data set.

public class EmployeeRepository
{
    public static List<Employee> AllEmployees()
    {
        var loc1 = new List<Location> { new Location { City = "Gretna", State = "VA", ZipCode = "24587" }, new Location { City = "Charlotte", State = "NC", ZipCode = "28012" } };
        var loc2 = new List<Location> { new Location { City = "Boston", State = "MA", ZipCode = "02333" }, new Location { City = "Waldham", State = "MA", ZipCode = "02323" } };
        var loc3 = new List<Location> { new Location { City = "Greenville", State = "NC", ZipCode = "29011" }};
        var loc4 = new List<Location> { new Location { City = "Greenville", State = "SC", ZipCode = "26000" }, new Location { City = "Charleston", State = "SC", ZipCode = "26011" } };

        return new List<Employee>()
        {
            new Employee {Id = 1, Department = new Department{Id = 1, Name = "Technology" },  Locations = loc1 },
            new Employee {Id = 2, Department = new Department{Id = 1, Name = "Technology" },  Locations = loc2},
            new Employee {Id = 3, Department = new Department{Id = 1, Name = "Technology" },  Locations = loc3 },
            new Employee {Id = 4, Department = new Department{Id = 2, Name = "IT" },  Locations = loc4 },
            new Employee {Id = 5, Department = new Department{Id = 2, Name = "IT" },  Locations = loc4 },
            new Employee {Id = 6, Department = new Department{Id = 3, Name = "Sales" },  Locations = loc3 },
            new Employee {Id = 7, Department = new Department{Id = 3, Name = "Sales" },  Locations = loc2},
            new Employee {Id = 9, Department = new Department{Id = 4, Name = "Marketing" },  Locations = loc2 },
            new Employee {Id = 9, Department = new Department{Id = 4, Name = "Marketing" },  Locations = loc1 },
        };
    }
}

Now I want to return all locations if the department name is given. My code is working

public List<Location> GetLocations(string name)
    {
        List<Location> locations = new List<Location>();
        var collection = EmployeeRepository.AllEmployees();
        var temp = (from e in collection where e.Department.Name == name select e);
        foreach(var item in temp)
        {
            locations.AddRange(item.Locations);
        }
        
        return locations.Distinct().ToList();
        
    }

But is there a better way in one linq query/method to do that?

UPDATE:

 public class Employee
{
    public int Id { get; set; }
    public Department Department { get; set; }
    public List<Location> Locations { get; set; }

    public decimal Salary { get; set; }
}

public class Location
{
    public string City { get; set; }
    public string State { get; set; }
    public string ZipCode { get; set; }
}
public class Department
{
    public int Id { get; set; }
    public string Name { get; set; }
}

Answer 1

Consider using records since none of your data change.

Consider using target typing so that your list initialisation is more terse.

Don't foreach - Linq indeed has in-built support for this.

Suggested

namespace StackExchange.EmployeeExample;

public record Department(
    int Id,
    string Name
) {}

public record Location(
    string City,   
    string State,  
    string ZipCode
) {}

public record Employee(
    int Id,
    Department Department,
    List<Location> Locations,
    decimal? Salary = null
) {}                                  

public class EmployeeRepository
{
    public static List<Employee> AllEmployees
    {
        get
        {
            var loc1 = new List<Location>
            {
                new(City: "Gretna", State: "VA", ZipCode: "24587"),
                new(City: "Charlotte", State: "NC", ZipCode: "28012"),
            };
            var loc2 = new List<Location>
            {
                new(City: "Boston", State: "MA", ZipCode: "02333"),
                new(City: "Waldham", State: "MA", ZipCode: "02323"),
            };
            var loc3 = new List<Location>
            {
                new(City: "Greenville", State: "NC", ZipCode: "29011"),
            };
            var loc4 = new List<Location>
            {
                new(City: "Greenville", State: "SC", ZipCode: "26000"),
                new(City: "Charleston", State: "SC", ZipCode: "26011"),
            };

            return new List<Employee>()
            {
                new(Id: 1, Department: new Department(Id: 1, Name: "Technology"), Locations: loc1),
                new(Id: 2, Department: new Department(Id: 1, Name: "Technology"), Locations: loc2),
                new(Id: 3, Department: new Department(Id: 1, Name: "Technology"), Locations: loc3),
                new(Id: 4, Department: new Department(Id: 2, Name: "IT"), Locations: loc4),
                new(Id: 5, Department: new Department(Id: 2, Name: "IT"), Locations: loc4),
                new(Id: 6, Department: new Department(Id: 3, Name: "Sales"), Locations: loc3),
                new(Id: 7, Department: new Department(Id: 3, Name: "Sales"), Locations: loc2),
                new(Id: 9, Department: new Department(Id: 4, Name: "Marketing"), Locations: loc2),
                new(Id: 9, Department: new Department(Id: 4, Name: "Marketing"), Locations: loc1),
            };
        }
    }

    public static List<Location> GetLocations(string departmentName) =>
        AllEmployees
        .Where(e => e.Department.Name == departmentName)
        .SelectMany(e => e.Locations)
        .Distinct()
        .ToList();

    public static void Main()
    {
        var result = GetLocations("Technology");
    }
}

Answer 2

Do you mean lambda expression?

If so you could simplify the code by using lambda expression as a parameter in the Where call, as follows:

public List<Location> GetLocations(string name)
{
    var collection = EmployeeRepository.AllEmployees();
    var locations = collection
        .Where(employee => employee.Department.Name == name)
        .SelectMany(employee => employee.Locations).Distinct().ToList();
    return locations;
}