过滤列表 <object> 另一个清单 <object2> C＃LINQ

Question

Consider following lists:

class user {
   public int id {get; set;}
   public string name {get; set;}
   public bool selected {get; set;} 
}

class coupon {
   public string username {get; set;}
   public string coupontype {get; set;}
   public string code {get; set;}
}

List<user> lUser = new List<user>();
List<coupon> lCoupon = new List<coupon>();

How is it possible (with LINQ ) to filter lCoupon with lUser so that the only values that remain are those with lCoupon.username field present in lUser.name , with lUser.selected being true ?

Pseudo code:

lCoupon = lCoupon.Where (w => lUser.name == w.name AND lUser.selected == true).ToList();

Answer 1

You could use the LINQ Any method on the lUser list, as in:

var coupons = lCoupon
    .Where(c => lUser.Any(u => u.selected && u.name == c.username))
    .ToList();

Answer 2

You can also do this with a join:

var coupons = from coupon in lCoupons
          join user in lUser on coupon.username equals user.name
          where user.selected
          select coupon; 

This way you can easely select values from both object types, eg:

var selectedObjects = from coupon in lCoupons
          join user in lUser on coupon.username equals user.name
          where user.selected
          select new { CouponCode = coupon.code, UserId = user.Id} ; 

You can ToList() this if you prefer.