How to add a column to IEnumerable list using linq query

Question

In my Controller Constructor I initialise my IEnumerable list which I will be passing it as model to my Views.

IEnumerable<classB> mdata;

public MyController()
{
   DataContext context = new DataContext(//connectionstring code missing//);
   mdata = context.GetTable<classB>().ToArray();
}

In my Action now I want to "add" a column to the mdata from a var list I retrieve from a Session as below:

var list = (List<Tuple<int,int>>)Session["ids"]; 

The list above contains id & Level both type int. The "id" will be used to match the rows in mdata which also have column "id". So once it finds a match it should add "Level" to the IEnumerable list. So far I have:

mdata = mdata.Where(x => list[].Item1.Contains(x.Id)); //not working

Answer 1

You cannot change your ClassB definition (add/remove properties at runtime) - Level property should exist there. But you can join both sequences by id and then select new anonymous object which will have level and joined ClassB instance:

var query = from b in mdata
            join t in list on b.Id equals t.Item1
            select new {
               B = b,
               Level = t.Item2
            };

Updating Level property in ClassB:

foreach(var pair in query)
   pair.B.Level = pair.Level;

---

Another option (you will avoid anonymous objects creation):

var levels = list.ToDictionary(t => t.Item1, t => t.Item2);
foreach(var b in mdata)
{
    int level;
    if (levels.TryGetValue(b.Id, out level))
        b.Level = level;
}