Question

All root categories in table have a PCATID of null.
The method actually does the job, sets cat to the very root
category, but then amazingly fails to return it once
it hits return cat; does some weird jumping in and
out of the “if” statement, then again to GetRootCat(cat);
and returns not the root category, but the first parent
category of cat.

Call:

listModel.PCATID = GetRootCat(cat).CategoryID;

Method:

    private Category GetRootCat(Category cat)
    {

        if (cat.PCATID != null)
        {
            cat = repository.Categories.FirstOrDefault(x => x.CategoryID == cat.PCATID);
            GetRootCat(cat);

        }

            return cat;
    }

Answer 1

Replace

GetRootCat(cat); 

with

return GetRootCat(cat);