[英]Get items from a list by ids of another list
抱歉,如果问题标题令人困惑,我有一个方案,其中有两个类User和Address。
public class User
{
public int userId { get; set; }
public string userName { get; set; }
public List<Address> address { get; set; }
}
public class Address
{
public string AddressLine { get; set; }
public string City { get; set; }
public string State { get; set; }
public int UserId { get; set; }
}
UserId是类地址中的外键,我有两个列表,即用户列表和地址列表。 用户中地址的值为空,我想获取每个用户的地址列表,我该如何实现? 我知道我们可以使用foreach,但是linq有办法实现吗? 下面是示例代码。
class Program
{
static void Main(string[] args)
{
var users = new List<User>();
users.Add(new User { userId = 1, userName = "User 1" });
users.Add(new User { userId = 2, userName = "User 2" });
users.Add(new User { userId = 3, userName = "User 3" });
users.Add(new User { userId = 4, userName = "User 4" });
var address = new List<Address>();
address.Add(new Address { AddressLine = "Address 1", City = "City 1", State = "State 1", UserId = 1 });
address.Add(new Address { AddressLine = "Address 1 Dup", City = "City 1", State = "State 1", UserId = 1 });
address.Add(new Address { AddressLine = "Address 2", City = "City 2", State = "State 2", UserId = 2 });
address.Add(new Address { AddressLine = "Address 2 Dup", City = "City 2", State = "State 2", UserId = 2 });
address.Add(new Address { AddressLine = "Address 3", City = "City 3", State = "State 3", UserId = 3 });
address.Add(new Address { AddressLine = "Address 3 Dup", City = "City 3", State = "State 3", UserId = 3 });
}
}
Linq
版本
List<User> result = users.Select(x =>
new User() {
userId = x.userId,
userName = x.userName,
address = address.Where(y => y.UserId == x.userId).ToList()
}).ToList();
imo foreach
版本更具可读性
foreach (User user in users)
user.address = address.Where(y => y.UserId == user.userId).ToList();
使用Select
和Where
相当简单。
users = users.Select(u => { u.address = address.Where(a => a.UserId == u.userId).ToList(); return u; }).ToList();
更具可读性的版本:
users = users.Select(u =>
{
u.address = address.Where(a => a.UserId == u.userId).ToList();
return u;
}).ToList();
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