Question

I have this objects:

notes:[ 
     { user: {
           name: "A",
           group:{
                id:1,
                name:"Group 1"
           }
     }, 
     { user: {
           name: "B",
           group:{
                id:1,
                name:"Group 1"
           }
    }]

and I need to group it by group.. so I tried this:

foreach (IGrouping<Group, Note> item in notes.GroupBy(n => n.User.Group))
{
    var groupName = item.Key.Name;

    foreach (var note in item)
    {
        //
    }
}

But I got a problem because grouping is not working(I think it’s because it uses references to group a complex type).
If I change n.User.Group by n.User.GroupId it works, but if I do it I can’t get the group name.

Answer 1

You need to override Equals and GetHashCode in Group class. R# generates this kind of code for it:

public class Group
{
    public int GroupId { get; set; }
    public string Name { get; set; }

    protected bool Equals(Group other)
    {
        return GroupId == other.GroupId;
    }

    public override bool Equals(object obj)
    {
        if (ReferenceEquals(null, obj)) return false;
        if (ReferenceEquals(this, obj)) return true;
        if (obj.GetType() != this.GetType()) return false;
        return Equals((Group) obj);
    }

    public override int GetHashCode()
    {
        return GroupId;
    }
}