LINQ的LEFT JOIN产生NULL引用异常

Question

I am trying to convert current code using JOIN to the LEFT JOIN using LINQ. This is the current code

 globalFunctions = _rolesAdapter.GetSecurityRightsForRole(SysManagerConstants.GLOBAL_DEFAULTS_ROLE_NUMBER, "SecFunc"). Select(secRight => new FuncViewModel() { Descrip = secRight.SecFunc.Descrip, FuncCode = secRight.SecFunc.FuncCode, Grouping = secRight.SecFunc.Grouping, Progmodule = secRight.SecFunc.Progmodule, SubCat = secRight.SecFunc.SubCat, GrantPerm = secRight.GrantPerm }).OrderBy(x => x.Descrip); //Unassigned editSecRoleViewModel.UnassignedFunctions = editSecRoleViewModel.UnassignedFunctions.Join(globalFunctions, uf => uf.FuncCode, gf => gf.FuncCode, (uf, gf) => new FuncViewModel() { Descrip = uf.Descrip, FuncCode = uf.FuncCode, Grouping = uf.Grouping, Progmodule = uf.Progmodule, SubCat = uf.SubCat, GrantPerm = (byte)(gf.GrantPerm | uf.GrantPerm), DefaultGrantPerm = gf.GrantPerm }).OrderBy(x => x.Descrip); 

My attempt to convert into LEFT JOIN based on the How do you perform a left outer join using linq extension methods

 //Unassigned editSecRoleViewModel.UnassignedFunctions = editSecRoleViewModel.UnassignedFunctions.GroupJoin(globalFunctions, uf => uf.FuncCode, gf => gf.FuncCode, (uf, gf) => new FuncViewModel() { Descrip = uf.Descrip, FuncCode = uf.FuncCode, Grouping = uf.Grouping, Progmodule = uf.Progmodule, SubCat = uf.SubCat, GrantPerm = (byte)(((int?)gf.FirstOrDefault().GrantPerm??1) | uf.GrantPerm), DefaultGrantPerm = (byte) ((int?)gf.FirstOrDefault().GrantPerm ?? 1) }).OrderBy(x => x.Descrip); 

I tried SingleOrDefault and FirstOrDefault and I keep getting the NULL object reference in run-time. The difference between the sample and my case is that I'm creating a new FuncViewModel object instead of just new. What should be done to correct the problem?

Answer 1

I solved it with this code

  //Unassigned editSecRoleViewModel.UnassignedFunctions = editSecRoleViewModel.UnassignedFunctions.SelectMany( uf => globalFunctions.Where(gf => uf.FuncCode== gf.FuncCode).DefaultIfEmpty(), (uf, gf) => new FuncViewModel() { Descrip = uf.Descrip, FuncCode = uf.FuncCode, Grouping = uf.Grouping, Progmodule = uf.Progmodule, SubCat = uf.SubCat, GrantPerm = (byte)( ((gf==null)?1:gf.GrantPerm) | uf.GrantPerm) , DefaultGrantPerm = ((gf == null) ? (byte)1 : gf.GrantPerm) }).OrderBy(x => x.Descrip);