在LINQ中加入两个列表，并写入其他列表

Question

I created a linq-select to join two lists.

var materialneu =
        (from material in ma
        join mb5b in mb
        on material.Mat_matwerk equals mb5b.Mb5b_matwerk
        into grouping
        from mb5b2 in grouping.DefaultIfEmpty()
        select new {material, zugang = (mb5b2 == null ? string.Empty : mb5b2.Mb5b_zugang.ToString())}).ToList();

I get no error, but zugang is always empty if I go through materialneu ... mb5b is definitely not empty, as well as the Mb5b_zugang . Also I would prefer to fill a field in my material-list, which already exists(but it is not filled yet). Is this possible? like

select new {material, material.zugang = mb5b3.Mb5b_zugang} 

? It allways gives me an error if I try it like this.

Answer 1

I hope it will work: Add Group

var materialneu =
    (from material in ma
    Group join mb5b in mb
    on material.Mat_matwerk equals mb5b.Mb5b_matwerk
    into grouping        
    from mb5b2 in grouping.DefaultIfEmpty()
    select new {material, zugang = (mb5b2 == null ? string.Empty : mb5b2.Mb5b_zugang.ToString())}).ToList();