Using LINQ to Entity - How can I join/concatenate columns from another table - vb.net

Question

I am having some issues with trying to figure out the correct way, or syntax, to join/concatenate a series of "name" columns from a separate table into a query.
Currently I am testing in LINQpad using two queries; the first returns all the master data that I use for other background work, and the second is a user-friendly version that I bind to a DGV. The issue comes in when I try to join the Physicians names like I do for a separate combobox.
This is what I have thus far - while it does return the Physician's name, it will NOT return the name if the TITLE field is NULL on the Physicians table.
Dim query1 = (From demog In data_Demogs
From MedHist In data_Demog_MedHists.where(Function(a) demog.ID_Demog = a.ID_Demog).defaultifempty
From BGLAssay In data_Demog_BGLs.where(Function(a) demog.ID_Demog = a.ID_Demog).defaultifempty
Select
demog.ID_Demog,
demog.Last_Name,
demog.First_Name,
demog.ID_Demog_AKA,
demog.DOB,
demog.Gender,
demog.ST_Complete,
demog.LT_Complete,
demog.LT_Due_Date,
demog.ID_Physician,
demog.ID_Reason_For_Call,
demog.Intl_Patient,
demog.Mayo_Patient,
MedHist.ID_Disease_Group,
MedHist.ID_Disease_Type,
BGLAssay.ID_BGL_Assay)
Dim query2 = (From items In query1
From demogAKA In data_Demogs.Where(Function(a) items.ID_Demog = a.ID_Demog_AKA).defaultifempty
From DType In tbl_Disease_Types.Where(Function(a) items.ID_Disease_Type = a.ID_Disease_Type).defaultifempty
From DGroup In tbl_Disease_Groups.Where(Function(a) items.ID_Disease_Group = a.ID_Disease_Group).defaultifempty
From RFC In tbl_Reason_For_Calls.Where(Function(a) items.ID_Reason_For_Call = a.ID_Reason_For_Call).defaultifempty
From Phys In tbl_Physicians.Where(Function(a) items.ID_Physician = a.ID_Physician).defaultifempty
From Title In tbl_Titles.Where(Function(a) Phys.ID_Title = a.ID_Title).defaultifempty
Select
items.ID_Demog,
items.Last_Name,
items.First_Name,
AKA_Name = demogAKA.Last_Name + ", " + demogAKA.First_Name,
items.DOB,
items.Gender,
items.ST_Complete,
items.LT_Complete,
items.LT_Due_Date,
DType.Disease_Type_Abr,
DGroup.Disease_Group_Name,
RFC.Reason_For_Call,
items.ID_Physician,
Phys_Name = Phys.Last_Name + ", " + Phys.First_Name + ", " + Title.Title
).distinct
console.writeline(Query2)
This is the currently query I for a combobox that DOES bring back all names, joining those names even if a field is NULL.
Dim Phys = (From e In tbl_Physicians
Group Join f In tbl_Titles On e.ID_Title Equals f.ID_Title
Into Matched = Group
From m In Matched.DefaultIfEmpty()
Select e.ID_Physician,
e.Last_Name,
e.First_Name,
e.Middle_Initial,
m.Title
).ToArray().Select(Function(item) New With {
.ID = item.ID_Physician,
.Phys_Name = (String.Join(", ",
String.Join(",",
New String() {item.Last_Name, item.First_Name, item.Title}).Split(
New Char() {","}, System.StringSplitOptions.RemoveEmptyEntries)))
})
Console.writeline(Phys)
When I try to add a third query to return just the Physician's name, and join that to the final query, I get the following error:
Local sequence cannot be used in LINQ to SQL implementations of query operators except the Contains operator.
'Query 1 removed to save space
Dim PhysNames = (From e In tbl_Physicians
Group Join f In tbl_Titles On e.ID_Title Equals f.ID_Title
Into Matched = Group
From m In Matched.DefaultIfEmpty()
Select e.ID_Physician,
e.Last_Name,
e.First_Name,
e.Middle_Initial,
m.Title
).ToArray().Select(Function(item) New With {
.ID = item.ID_Physician,
.Phys_Name = (String.Join(", ",
String.Join(",",
New String() {item.Last_Name, item.First_Name, item.Title}).Split(
New Char() {","}, System.StringSplitOptions.RemoveEmptyEntries)))
})
Dim query2 = (From items In query1
From demogAKA In data_Demogs.Where(Function(a) items.ID_Demog = a.ID_Demog_AKA).defaultifempty
From DType In tbl_Disease_Types.Where(Function(a) items.ID_Disease_Type = a.ID_Disease_Type).defaultifempty
From DGroup In tbl_Disease_Groups.Where(Function(a) items.ID_Disease_Group = a.ID_Disease_Group).defaultifempty
From RFC In tbl_Reason_For_Calls.Where(Function(a) items.ID_Reason_For_Call = a.ID_Reason_For_Call).defaultifempty
From Phys In PhysNames.Where(Function(a) items.ID_Physician = a.ID).defaultifempty
Select
items.ID_Demog,
items.Last_Name,
items.First_Name,
AKA_Name = demogAKA.Last_Name + ", " + demogAKA.First_Name,
items.DOB,
items.Gender,
items.ST_Complete,
items.LT_Complete,
items.LT_Due_Date,
DType.Disease_Type_Abr,
DGroup.Disease_Group_Name,
RFC.Reason_For_Call,
items.ID_Physician,
Phys.Phys_Name
).distinct
console.writeline(Query2)
When I try to join my working query into the final query, I get the following error:
Invalid cast from 'System.String' to 'VB$AnonymousDelegate_0`2[[System.Object, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934...
'Query1 removed to save space
Dim query2 = (From items In query1
From demogAKA In data_Demogs.Where(Function(a) items.ID_Demog = a.ID_Demog_AKA).defaultifempty
From DType In tbl_Disease_Types.Where(Function(a) items.ID_Disease_Type = a.ID_Disease_Type).defaultifempty
From DGroup In tbl_Disease_Groups.Where(Function(a) items.ID_Disease_Group = a.ID_Disease_Group).defaultifempty
From RFC In tbl_Reason_For_Calls.Where(Function(a) items.ID_Reason_For_Call = a.ID_Reason_For_Call).defaultifempty
From Phys In tbl_Physicians
Where items.ID_Physician = Phys.ID_Physician
Group Join f In tbl_Titles On Phys.ID_Title Equals f.ID_Title
Into Matched = Group
From m In Matched.DefaultIfEmpty()
Select
items.ID_Demog,
items.Last_Name,
items.First_Name,
AKA_Name = demogAKA.Last_Name + ", " + demogAKA.First_Name,
items.DOB,
items.Gender,
items.ST_Complete,
items.LT_Complete,
items.LT_Due_Date,
DType.Disease_Type_Abr,
DGroup.Disease_Group_Name,
RFC.Reason_For_Call,
items.ID_Physician,
PhysName = Function(a) String.Join(", ",
String.Join(",",
New String() {Phys.Last_Name, Phys.First_Name, m.Title}).Split(
New Char() {","}, System.StringSplitOptions.RemoveEmptyEntries))
).distinct
console.writeline(Query2)

Answer 1

After a long time playing around in LINQpad, and then finally re-reading JM's answer to a former question I had, I realized what I was doing wrong.
As per his post:
The problem is that, while LINQ in general has no issue with that code, LINQ to Entities does. LINQ syntax is the same for every provider but the implementation under the hood differs and, in the case of LINQ to Entities, your LINQ code has to translated to SQL and, in this case, there's no mapping from String.Join to SQL. That code would work fine with LINQ to Objects so one solution is to push that operation out of the original query and into a LINQ to Objects query. That would mean selecting the raw data with your LINQ to Entities query, calling ToList or ToArray on the result to materialise the query, then performing another query on that result. That second query will be LINQ to Objects rather than LINQ to Entities and so String.Join will not be an issue.
So... Once I realized I needed to push out the String.Join, I ended up with the following code:
Dim DispList = (From items In MastList
From demogAKA In dbACL.data_Demog.Where(Function(a) items.ID_Demog = a.ID_Demog_AKA).DefaultIfEmpty
From DType In dbACL.tbl_Disease_Type.Where(Function(a) items.ID_Disease_Type = a.ID_Disease_Type).DefaultIfEmpty
From DGroup In dbACL.tbl_Disease_Group.Where(Function(a) items.ID_Disease_Group = a.ID_Disease_Group).DefaultIfEmpty
From RFC In dbACL.tbl_Reason_For_Call.Where(Function(a) items.ID_Reason_For_Call = a.ID_Reason_For_Call).DefaultIfEmpty
From e In dbACL.tbl_Physician.Where(Function(a) items.ID_Physician = a.ID_Physician).DefaultIfEmpty
Group Join f In dbACL.tbl_Title On e.ID_Title Equals f.ID_Title
Into Matched = Group
From m In Matched.DefaultIfEmpty()
Select
items.ID_Demog,
items.Last_Name,
items.First_Name,
AKALname = demogAKA.Last_Name,
AKAFname = demogAKA.First_Name,
items.DOB,
items.Gender,
items.ST_Complete,
items.LT_Complete,
items.LT_Due_Date,
DType.Disease_Type_Abr,
DGroup.Disease_Group_Name,
RFC.Reason_For_Call,
items.ID_Physician,
PLName = e.Last_Name,
PFname = e.First_Name,
PMI = e.Middle_Initial,
PTitle = m.Title
).Distinct.ToList().Select(Function(a) New With {
a.ID_Demog,
a.Last_Name,
a.First_Name,
.AKA_Name = (String.Join(", ",
String.Join(",",
New String() {a.AKALname, a.AKAFname}).Split(
New Char() {","}, System.StringSplitOptions.RemoveEmptyEntries))),
a.DOB,
a.Gender,
a.ST_Complete,
a.LT_Complete,
a.LT_Due_Date,
a.Disease_Type_Abr,
a.Disease_Group_Name,
a.Reason_For_Call,
a.ID_Physician,
.PName = (String.Join(", ",
String.Join(",",
New String() {a.PLName, a.PFname, a.PTitle}).Split(
New Char() {","}, System.StringSplitOptions.RemoveEmptyEntries)))
}).ToList()