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EF Core Distinct + OrderBy Throws Translation Error

I have been dealing with a really frustrating EF Core (newest version) error. I'm not sure at this point if I am doing something wrong or if it's a bug. Any help the community can provide would be appreciated.
The error is in regards to Entity Framework Core and translating a LINQ expression to SQL. The below code translates to SQL properly. The query variable below could potentially have a variety of Where expressions and Includes applied to it with no issue.
// This works fine
query.Select(price => new Customer {
Name = price.Payer.Name,
Code = price.Payer.Code,
City = price.Payer.City,
ParentCode = price.Payer.ParentCode,
ParentLevel = CustomerLevel.Corporate,
CustomerLevel = CustomerLevel.Payer
}).Distinct().ToListAsync();
As soon as I add a call to OrderBy, it will not evaluate. If I remove the call to Distinct, it once again works, but I can't have both. I've tried several different ways to build the expression and several workarounds that I've found around the interwebz, and nothing seems to resolve it.
// This throws error
// query is of type IQueryable<Price>
query.Select(price => new Customer {
Name = price.Payer.Name,
Code = price.Payer.Code,
City = price.Payer.City,
ParentCode = price.Payer.ParentCode,
ParentLevel = CustomerLevel.Corporate,
CustomerLevel = CustomerLevel.Payer
}).Distinct().OrderBy(cust => cust.Name).ToListAsync();
Also, placement of the OrderBy does not seem to matter. Based on what I've read, the call to Distinct removes all prior ordering, so this one is not too surprising.
// This also throws error
// query is of type IQueryable<Price>
query
.OrderBy(price => price.payer.Name)
.Select(price => new Customer {
Name = price.Payer.Name,
Code = price.Payer.Code,
City = price.Payer.City,
ParentCode = price.Payer.ParentCode,
ParentLevel = CustomerLevel.Corporate,
CustomerLevel = CustomerLevel.Payer
}).Distinct().ToListAsync();

I actually found the cause of the issue today. The ParentCode property (used at line ParentCode = price.Payer.ParentCode) is actually a property on the base class that is not mapped to the table, so EF apparently did not know what to do with it. The very strange part of this is that it worked without the OrderBy. Changing that line to ParentCode = price.Payer.CorporateCode resolved the issue.
Thanks for anyone that took a look at this.

Cannot add an entity with a key that is already in use update operation

I am creating small application in which i have used LINQ To SQL to perform all operation to database.
Now here i am giving the small part of my database structure please take a look.
So update language detail i am getting the object of login using the datacontext something like this.
XVDataContext Context = new XVDataContext ();
var myQuery = from objLogIn in Context.GetTable<LogIn>() where objLogIn.Emp_Id == nEmpId select objLogIn;
In nEmpId i will always have some value.
So it is not creating any problem in fact i am getting the required record from DB and storing it in objUser object using the following code.
LogIn objUser = myQuery.First<LogIn>();
Now to update LanguageDetail i am executing following code but it throws Exception when i execute SubmitChanges line.
Here is the code that i am executing to update.
LanguageDetail obj = new LanguageDetail();
foreach (string sLanguages in TextBoxLanguagesKnown.Text.Split('\n'))
{
obj.Emp_Id = objUser.Emp_Id;
obj.Language = sLanguages.Trim();
}
objUser.LanguageDetails[0] = obj;
Context.SubmitChanges();
I already read following links.
cannot add an entity with a key that is already in use
LINQ To SQL exception with Attach(): Cannot add an entity with a key that is alredy in use
Cannot add an entity with a key that is already in use (LINQ)
By reading the above links i found that i am doing some mistake in ID fields but still i am unable to resolve.
Please tell me the clear understanding of raising this issue and how can i resolve this.
EDIT:
I simply want to update LanguageDetail table.
When i try to add new object using following code it still throws exception.
objUser.LanguageDetail.Add(obj);

You might want to add / remove languages for specific user by using following code.
var languages = TextBoxLanguagesKnown.Text.Split('\n');
// Removes deleted languages (first find all language details that are missing from the UI).
var deletedLanguages = objUser.LanguageDetails.Where(ld => !languages
.Any(l => ld.Language == l.Trim())).ToArray();
foreach(var deletedLanguage in deletedLanguages)
{
objUser.LanguageDetails.Remove(deletedLanguage);
Context.LanguageDetails.DeleteOnSubmit(deletedLanguage);
}
// Adds new languages (then adds new language details that are not found in the database).
var newLanguages = languages.Where(l => !objUser.LanguageDetails
.Any(ld => ld.Language == l.Trim())).ToArray();
foreach (string newLanguage in newLanguages)
{
var languageDetail = new LanguageDetail
{
Emp_Id = objUser.Emp_Id,
Language = newLanguage.Trim()
};
objUser.LanguageDetails.Add(languageDetail);
}
Context.SubmitChanges();

From my understanding you want to update the LanguageDetail entity in your database. In order to do so you have to do one of the following:
Retrieve the original LanguageDetail object based on its id, and update that object instead of creating a new one and assigning it the id of an existing object.
Attach the newly created object to your context instead of just giving a reference to it to your LanguageDetails collection.
The exception you are seeing happens because the way linq to sql behaves is that it threats the obj as a new object that you want to insert and because of that it tries to insert it into the language details table.
Modifying your code like that should work:
Context.LanguageDetails.Attach(obj);
objUser.Employee_LanguageDetails[0] = obj;

Trying to update a DataRow in C# with LINQ

I'm trying to find, then update, a specific DataRow in a DataTable. I've tried a few things based on my searches, and the code below seems to be the closest I can get. The linq will return one row. With that row, I'd like to update column values (Status, StopTime, Duration). I can't for the life of me find how to do this.. I've tried casting, but I'm new to linq and don't see how to update these values.
private DataTable downloadProcStatusTable;
void UpdateDataDownloadProcedureList(ProcedureStats ProcStats)
{
var currentStatRow = from currentStat in downloadProcStatusTable.AsEnumerable()
where currentStat.Field<String>("ProcedureName") == ProcStats.ProcName
select currentStat;
}

Your query as it stands actually gives you an IEnumerable<DataRow>. You need to do this to get the actual row:
var currentStatRow = (from currentStat in downloadProcStatusTable.AsEnumerable()
where currentStat.Field<String>("ProcedureName") == ProcStats.ProcName
select currentStat).SingleOrDefault();
You should then be able to use the currentStatRow variable to modify the column values.

Outline
Load the existing entity from the database (unless you have one that you can re-attach, in which case you could avoid this additional query)
Update the properties as needed
Submit the changes back to the database using SubmitChanges()
Implementation
I wasn't exactly sure where your variables are and the names, but this should give you a good start...
void UpdateDataDownloadProcedureList(ProcedureStats ProcStats)
{
var currentStatRow = (from currentStat in downloadProcStatusTable.AsEnumerable()
where currentStat.Field<String>("ProcedureName") == ProcStats.ProcName
select currentStat).FirstOrDefault();
currentStatRow.Status = ProcStats.Status;
currentStatRow.StopTime = ProcStats.StopTime;
currentStatRow.Duration = ProcStats.Duration;
downloadProcStatusTable.SubmitChanges();
}

Why can't I update data into database using LINQ to SQL?

I am trying to update data while I am reading them from database, see below. But after the whole thing finish, the data didn't get updated.(my table has primary key ).
static LinqMPISMPPCalenderDataContext DBCalender;
DBCalender = new LinqMPISMPPCalenderDataContext(connectionString);
var ExceptionPeriod= DBCalender.Table_ExceptionPeriods
.Where(table=>Table.StartDate<= Date && table.FinishDate >= Date && table.CalenderID==CalenderID).Single();
Table_ExceptionPeriod TblException =null;
TblException = ExceptionPeriod;
TblException.StartDate = ExceptionPeriod.StartDate.AddDays(1);
DBCalender.SubmitChanges();

Once you've got your object from the DB via your .Single() call you should be able to just set properties on it and call SubmitChanges(). There's no need for the TblException stuff. So ...
static LinqMPISMPPCalenderDataContext DBCalender;
DBCalender = new LinqMPISMPPCalenderDataContext(connectionString);
var ExceptionPeriod = DBCalender.Table_ExceptionPeriods
.Where(table=>Table.StartDate<= Date && table.FinishDate >= Date && table.CalenderID==CalenderID).Single();
ExceptionPeriod.StartDate = ExceptionPeriod.StartDate.AddDays(1);
DBCalender.SubmitChanges();

There doesn't seem to be anything logically wrong with the code, as Antony says you could reduce the number of lines.
I'd probably step through the code line by line, before the submit line check if the StartDate has actually changed.
Only things I can imagine that could be going wrong are some kind of transaction roll back in the database or you're not looking at the record you think you are.

Correctly incrementing values using Linq to SQL

I have a MS SQL table that I don't have any control over and I need to write to. This table has a int primary key that isn't automatically incremented. I can't use stored procs and I would like to use Linq to SQL since it makes other processing very easy.
My current solution is to read the last value, increment it, try to use it, if I get a clash, increment it again and retry.
Something along these lines:
var newEntity = new Log()
{
ID = dc.Logs.Max(l => l.ID) + 1,
Note = "Test"
};
dc.Logs.InsertOnSubmit(newEntity);
const int maxRetries = 10;
int retries = 0;
bool success = false;
while (!success && retries < maxRetries)
{
try
{
dc.SubmitChanges();
success = true;
}
catch (SqlException)
{
retries++;
newEntity.ID = dc.Logs.Max(l => l.ID);
}
}
if (retries >= maxRetries)
{
throw new Exception("Bummer...");
}
Does anyone have a better solution?
EDIT: Thanks to Jon, I simplified the max ID calculation. I was still in SQL thinking mode.

That looks like an expensive way to get the maximum ID. Have you already tried
var maxId = dc.Logs.Max(s => s.ID);
? Maybe it doesn't work for some reason, but I really hope it does...
(Admittedly it's more than possible that SQL Server optimises this appropriately.)
Other than that, it looks okay (smelly, but necessarily so) to me - but I'm not an expert on the matter...

You didn't indicate whether your app is the only one inserting into the table. If it is, then I'd fetch the max value once right after the start of the app/webapp and use Interlocked.Increment on it every time you need next ID (or simple addition if possible race conditions can be ruled out).

You could put the entire operation in a transaction, using a TransactionScope class, like below:
using (TransactionScope scope = new TransactionScope()){
var maxId = dc.Logs.Max(s => s.ID);
var newEntity = new Log(){
ID = maxId,
Note = "Test"
};
dc.Logs.InsertOnSubmit(newEntity);
dc.SubmitChanges();
scope.Complete();
}
By putting both the retrieval of the maximum ID and the insertion of the new records within the same transaction, you should be able to pull off an insert without having to retry in your manner.
One problem you might face with this method will be transaction deadlocks, especially if the table is heavily used. Do test it out to see if you require additional error-handling.
P.S. I included Jon Skeet's code to get the max ID in my code, because I'm pretty sure it will work correctly. :)

Make the id field auto incrementing and let the server handle id generation.
Otherwise, you will run into the problem liggett78 said. Nothing prevents another thread from reading the same id in between the reading and submitting of max id for this thread.