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'The cast to value type 'System.Double' failed because the materialized value is null [duplicate]

I have the following code. I'm getting error:
"The cast to value type 'Int32' failed because the materialized value is null. Either the result type's generic parameter or the query must use a nullable type."
when CreditHistory table has no records.
var creditsSum = (from u in context.User
join ch in context.CreditHistory on u.ID equals ch.UserID
where u.ID == userID
select ch.Amount).Sum();
How can I modify the query to accept null values?

A linq-to-sql query isn't executed as code, but rather translated into SQL. Sometimes this is a "leaky abstraction" that yields unexpected behaviour.
One such case is null handling, where there can be unexpected nulls in different places. ...DefaultIfEmpty(0).Sum(0) can help in this (quite simple) case, where there might be no elements and sql's SUM returns null whereas c# expect 0.
A more general approach is to use ?? which will be translated to COALESCE whenever there is a risk that the generated SQL returns an unexpected null:
var creditsSum = (from u in context.User
join ch in context.CreditHistory on u.ID equals ch.UserID
where u.ID == userID
select (int?)ch.Amount).Sum() ?? 0;
This first casts to int? to tell the C# compiler that this expression can indeed return null, even though Sum() returns an int. Then we use the normal ?? operator to handle the null case.
Based on this answer, I wrote a blog post with details for both LINQ to SQL and LINQ to Entities.

To allow a nullable Amount field, just use the null coalescing operator to convert nulls to 0.
var creditsSum = (from u in context.User
join ch in context.CreditHistory on u.ID equals ch.UserID
where u.ID == userID
select ch.Amount ?? 0).Sum();

Had this error message when I was trying to select from a view.
The problem was the view recently had gained some new null rows (in SubscriberId column), and it had not been updated in EDMX (EF database first).
The column had to be Nullable type for it to work.
var dealer = Context.Dealers.Where(x => x.dealerCode == dealerCode).FirstOrDefault();
Before view refresh:
public int SubscriberId { get; set; }
After view refresh:
public Nullable<int> SubscriberId { get; set; }
Deleting and adding the view back in EDMX worked.
Hope it helps someone.

I have used this code and it responds correctly, only the output value is nullable.
var packesCount = await botContext.Sales.Where(s => s.CustomerId == cust.CustomerId && s.Validated)
.SumAsync(s => (int?)s.PackesCount);
if(packesCount != null)
{
// your code
}
else
{
// your code
}

You are using aggregate function which not getting the items to perform action , you must verify linq query is giving some result as below:
var maxOrderLevel =sdv.Any()? sdv.Max(s => s.nOrderLevel):0

I see that this question is already answered. But if you want it to be split into two statements, following may be considered.
var credits = from u in context.User
join ch in context.CreditHistory
on u.ID equals ch.UserID
where u.ID == userID
select ch;
var creditSum= credits.Sum(x => (int?)x.Amount) ?? 0;

Got this error in Entity Framework 6 with this code at runtime:
var fileEventsSum = db.ImportInformations.Sum(x => x.FileEvents)
Update from LeandroSoares:
Use this for single execution:
var fileEventsSum = db.ImportInformations.Sum(x => (int?)x.FileEvents) ?? 0
Original:
Changed to this and then it worked:
var fileEventsSum = db.ImportInformations.Any() ? db.ImportInformations.Sum(x => x.FileEvents) : 0;

I was also facing the same problem and solved through making column as nullable using "?" operator.
Sequnce = db.mstquestionbanks.Where(x => x.IsDeleted == false && x.OrignalFormID == OriginalFormIDint).Select(x=><b>(int?)x.Sequence</b>).Max().ToString();
Sometimes null is returned.

MySQL Entity Framework With LinQ Correlated Query Not Executing

I am using Visual Studio 2012 with MySQL 5.7 Community Edition. I am getting object reference not set to an instance of object on the below query.
var oList = (
from dm in dbContext.document_master
join um in dbContext.user_master on dm.Alocated_CAA equals um.UserId
where (dm.DocumentHandle != null)
select new TaskLogReport
{
documentDate = dm.Document_Date,
documentHandle = dm.DocumentHandle,
fileNumber = dm.FileNumber,
statusRemarks = dbContext.statushistories
.Where(x => x.DocumentHandle == 12345678).FirstOrDefault().Remarks
}).ToList();
In the above query If I get change 12345678 to dm.DocumentHandle, then getting object reference not set to an instance object.
Try with MS-SQL server , working fine.

You get the error because FirstOrDefault() returns null, because there are no objects who's DocumentHandle equals dm.DocumentHandle. Changing dm.DocumentHandle to 12345678 works because there is one matching element.
This line is the problem:
.Where(x => x.DocumentHandle == 12345678).FirstOrDefault().Remarks
C#'s Enumerable.FirstOrDefault() method returns either the first matching element of an enumerable, or, if there aren't any, the default value of the type. In the case of nullable types, FirstOrDefault() returns null if no elements are found.
The reason you get no error when you use 12345678 is because there is at least one matching value with that DocumentHandle. However, when you change that to dm.DocumentHandle, no matching elements are found, causing FirstOrDefault to return null. Then you essentially do null.Remarks, which causes the error.
You should change your code to this:
.FirstOrDefault(x => x.DocumentHandle == dm.DocumentHandle)?.Remarks
There are two differences here:
Got rid of the where and moved the predicate to the FirstOrDefault call. This is just a cleaner way of doing what you were doing before.
Added the ? at the end of the FirstOrDefault call. That is the null propagation operator.
What it does is it turns this:
int foo;
if (bar != null)
{
foo = bar.foo;
}
Into this:
int foo = bar?.foo;
Now, if there are matching elements, statusRemarks will be equal to the first one's Remarks. Otherwise, statusRemarks will be null.
EDIT: The null propagation operator was implemented in C# 6.0, which is .Net 4.6 onwards, so it won't work in .Net 4.0.
You'll have to modify your query and implement a check, like so:
var oList = (
from dm in dbContext.document_master
join um in dbContext.user_master on dm.Alocated_CAA equals um.UserId
where (dm.DocumentHandle != null && dbContext.statushistories.Count(x => x.DocumentHandle == dm.DocumentHandle) > 0)
select new TaskLogReport
{
documentDate = dm.Document_Date,
documentHandle = dm.DocumentHandle,
fileNumber = dm.FileNumber,
statusRemarks = dbContext.statushistories.First(x.DocumentHandle == dm.DocumentHandle).Remarks
}).ToList();

Entity Framework - Linq to Entities - Optional filter

I am struggling to figure out how to get a LINQ statement to produce a specific WHERE clause in SQL in a single statement.
I am after it producing something like this:
SELECT ColA, ColB, ColC, ColN...
FROM Orders
WHERE Client = #ClientId
AND (#CompanyId IS NULL OR #CompanyId = CompanyId)
My (failing) LINQ statement looks like this:
var includeAllCompanies = company == null;
var data = context.Orders.Where(o => o.Client.Id == clientId
&& (includeAllCompanies
|| (c.Company != null && c.Company.Id == company.Id)).ToList();
However, it always throws an exception when the variable company is NULL (it works fine when it has been initialised). The exception being:
Non-static method requires a target.
My current fix is to split my LINQ statement into two. One using an Expression<Func<>> (to be transformed to a SQL statement with partial filtering). Then another that uses Func<> to perform the remaining filters on the returned list.
Expression<Func<>> to let SQL do some of the work (excluding nullable objects)
var data = context.Orders.Where(o => o.Client.Id == clientId).ToList();
Func<> to then filter out the nullable objects
data = data.Where(c => (territory == null
|| (c.Territory != null && c.Territory.Id == territory.Id))).ToList();
This works, however, I want SQL to be performing this query.

The problem is that, company is server-side variable. Regardles includeAllCompanies value, EF has to translate whole LINQ query to SQL - and in this case SQL doesn't know what is company.Id - so EF has to always get company.Id value in order to put into SQL query. Even if company is null (so that is why you get exception). I hope you see my point, if not - I'll try to give some sample.
In order get rid of exception you can do the following:
var companyId = company == null ? null : (int?)company.Id;
var data = context.Orders.Where(o => o.Client.Id == clientId
&& (companyId == null
|| (c.Company != null && c.Company.Id == companyId)).ToList();

linq join on guid and string column

I'm new to linq. I need to run a query that joins two columns (AnonymousUser.AnonymousId being uniqueidentifier and comment.UserId being nvarchar(100)), something like below:
using (CommentEntities db = new CommentEntities())
{
// filteredComments is a query that is not run until the next .ToList()
IQueryable<Comment> filteredComments = this.CommentGetList(...);
var query = from comment in filteredComments
// following line is the syntax error, because columns' types don't match
join user in db.AnonymousUsers on comment.UserId equals user.AnonymousId into gj
from userNull in gj.DefaultIfEmpty()
select new CommentWithName
{
Comment = comment,
UserId = comment.UserId,
FirstName = (userNull == null ? "" : userNull.Name),
LastName = "",
Email = (userNull == null ? "" : userNull.Email)
};
return query.ToList();
}
First I was happy writing the query with .ToString() ! As it turns out that entity framework doesn't know how to translate it to sql. The same is true for Guid.Parse(string). Also new Guid(string) cannot be used in linq to entities (only parameterless constructors allowed)!
So after searching, I found out it's not possible doing such thing in EF 4.0! I migrated my code to a stored procedure that I'm not really happy about it.
Is it possible to tell entity framework to use a CAST in SQL?
Is there any solutions to this problem? Is there any way that I can bring the logic in code?
NOTE: I meant to do it in one GO. Otherwise one possible solution is to get Entities from first table, and put the Ids in a list and get entities from second table.

call toList() before applying those methods. Like:
var Product = db.Products.Where(p => p.ProductId == Guid.Parse("B4E913F9-166C-49BA-AADE-6DB889D1756F")).Single();
Would throw a
c# LINQ to Entities does not recognize the method "System.Guid Parse" (System.String)' method, and this method cannot be translated into a store expression
But this works:
var Product = db.Products.ToList().Where(p => p.ProductId == Guid.Parse("B4E913F9-166C-49BA-AADE-6DB889D1756F")).Single()
p.s.: I think you will lose lazyloading but you can do eagerloading with .Include before calling .ToList().

If your list is object list you could convert it to the type which has Guid as identifier, first create new anonymous type and then filter it base on UserId, sure UserId which is of type int, wont include in join:
int output = 0;
var secondList = list.Where(x=>!int.TryParse(x.UserID, out output))
.Select(x=>new {Comment = x, ID = new Guid(x.UserID))
.ToList();
Now you could run your query on db by using secondList.

Linq IN in C# error

I'm trying to do this:
myList = (from c in ipE.Cars
where (someListOfIntegers.Contains(idCar) && c.name == someName)
select c).ToList();
I'm getting the eror LINQ to Entities does not recognize the method 'Boolean Contains(Int32)' method, and this method cannot be translated into a store expression.
I tried with ANY, it still doesn't work. I got the error Unable to create a constant value of type 'Closure type'. Only primitive types ('such as Int32, String, and Guid') are supported in this context.
How to resolve this?

Unfortunately, you cant't use local collections in an EF query. You can work around it, by using the PredicateBuilder and translate the Contains operation manually in a sequence of ORs:
var predicate = PredicateBuilder.False<Car>();
foreach (int id in someListOfIntegers)
{
int temp = id;
predicate = predicate.Or (car => car.idCar == id);
}
myList = (from c in ipE.Cars
where predicate && c.name == someName)
select c).ToList();
Sidenote: I assume, that you have a typo in your question, because neither someListOfIntegers nor idCar are properties of your EF model you query. So i guess you want to query for Car.idCar?.
Otherwise you just could refactor the Contains completely out of the EF query.

You seem to be suggesting (comments) that idCar does not relate to any entities - in which case, don't do that in the query:
List<Car> list;
if(someListOfIntegers.Contains(idCar)) {
myList = (from c in ipE.Cars
where c.name == someName
select c).ToList();
} else {
myList = new List<Car>(); // no need to touch the DB
}

Seen the same myself: L2E uses a small set of commands - and there isn't a "Contains(Int32)" command.
If your lists are fairly small, then try adding ".AsEnumerable()", which will execute the T-SQL select statements and leave you with POCO objects which CAN use Contains.
e.g.
myList = (from c in ipE.Cars.AsEnumerable
where (someListOfIntegers.AsEnumerable().Contains(idCar)
&& c.name == someName)
select c)
.ToList();
Not sure if you need both AsEnumerables...try it out!