Possible multiple enumeration - jak uniknąć

class Foo
{
    public int Id { get; set;}
    public string Boo { get; set;}
}

public IEnumerable<Foo> Do(IEnumerable <Foo> foos)
{
    var ids = foos.Select(x => x.Id);
    var cache = api.Get(ids);
    foreach(var foo in foos)
    {
        var someData = cache.TryGetValue(foo.Id);
        if(someData != null)
        {
            foo.Boo = someData;
        }
        else 
        { //something else
        }
     yield return foo;
    }
}

public IEnumerable<obj> Do(IEnumerable<int> IDs, int PageSize)

public class obj
        {
            public obj(int Id, string Value)
            {
                this.Id = Id;
                this.Value = Value;
            }

            public int Id { get; set; }
            public string Value { get; set; }
        }
        public class api
        {
            public static IEnumerable<obj> Get(IEnumerable<int> IDs)
            {
                Random random = new Random();
                foreach (int id in IDs)
                    yield return new obj(id, random.Next(100, 10000).ToString());
            }
        }

        public IEnumerable<obj> Do(IEnumerable<int> IDs, int PageSize)
        {
            int n = 0;
            do
            {
                bool LastLoop = (IDs.Count() <= n + PageSize) ? true : false;
                IEnumerable<int> IDsInCurrentLoop = (LastLoop) ? IDs.ToList().GetRange(n, PageSize) : IDs.ToList().GetRange(n, IDs.Count() - n);
                IEnumerable<obj> importedData = api.Get(IDsInCurrentLoop);
                foreach (obj o in importedData)
                    yield return o;
                n += PageSize;
            } while (n >= IDs.Count());
        }

     foreach(var foo in foos)
     {
         var cache = api.Get(new List<int> { foo.Id });
         // ...
     }