Question

I have 2 lists with some data in:

List1.Add(new Filter { Name = "Foo", Value = "Bar" });
List2.Add(new Filter { Name = "Foo", Value = "Bar" });

I would like to use Linq to return true if List1 contains ALL the values in List2, the example above would obviously return true but this is an example but if I added

List2.Add(new Filter { Name = "Foo1", Value = "Bar1" });

then it should return false.

I started going down the lines of:

var Result = from item1 in List1
             join item2 in List2 on item1.Name equals item2.Name
             new { item1, item2 };

but this would only match on the Name and I’m pretty sure I am going down the wrong route with this.

EDIT: Just to clarify, I don’t want only the VALUE property. Name && Value must match in both lists.

Answer 1

You can use Except:

var l1Vals = List1.Select(f => f.Value);
var l2Vals = List2.Select(f => f.Value);
var notInL1 = l2Vals.Except(l1Vals);
if(notInL1.Any())
{
    // no, not all Values of List2 are in List1
}

Edit According to your last edit that you want to compare all properties of Filter, the best approach is to create a custom IEqualityComparer<Filter> and use that as argument for this Enumerable.Except overload:

public class Filter {
    public String Name { get; set; }
    public String Value { get; set; }

    public class Comparer : IEqualityComparer<Filter>
    {
        public bool Equals(Filter x, Filter y)
        {
           if(ReferenceEquals(x, y))
               return true;
           else if(x==null || y==null)
               return false;
           return x.Name  == y.Name
               && x.Value == y.Value;
        }

        public int GetHashCode(Filter obj)
        {
            unchecked 
            {
                int hash = 17;
                hash = hash * 23 + obj.Name.GetHashCode();
                hash = hash * 23 + obj.Value.GetHashCode();
                return hash;
            }
        }
    }
}

Now this works:

var notInL1 = List2.Except(List1, new Filter.Comparer());
if (notInL1.Any())
{
    // no, not all properties of all objects in List2 are same in List1
    // notInL1 contains the set difference
}