Error: Sequence contains no elements

Question

Hi NG,

 

I'm using the following statemtn to get a record from my database

 

Code Snippet

var productItem = productDtcx.Product.Single(p => p.ProductNumber == "TP00002");

 

 

In case, when this record is not existing in my database I'm receiving the following exception:

 

Code Snippet

System.InvalidOperationException was unhandled
  Message="Sequence contains no elements"
  Source="System.Core"
  StackTrace:
       at System.Linq.Enumerable.Single[TSource](IEnumerable`1 source)
       at System.Data.Linq.SqlClient.SqlProvider.SqlQueryResults`1.PostProcess(Expression query, IEnumerable`1 results)
       at System.Data.Linq.SqlClient.SqlProvider.SqlQueryResults`1.GetEnumerator()
       at System.Linq.Enumerable.Single[TSource](IEnumerable`1 source)
       at System.Data.Linq.Table`1.System.Linq.IQueryable.Execute[S](Expression expression)
       at System.Linq.Queryable.Single[TSource](IQueryable`1 source, Expression`1 predicate)
       at Sample0040.Program.Main(String[] args) in C:\Documents and Settings\oaytekin\Desktop\LINQSamples\Sample0040\Program.cs:line 19
       at System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args)
       at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
  InnerException:

 

 

I don't want to catch this exception with a try/catch block. Is there any another method/way to check, if a record is existing or not?

 

I want to delete a record. To get and delete the record I'm using the following code

 

Code Snippet

string connString = "Data Source=.;Initial Catalog=AdventureWorks;Integrated Security=True";

 

ProductDataContext productDtcx = new ProductDataContext(connString);

 

var productItem = productDtcx.Product.Single(p => p.ProductNumber == "TP00002");

 

productDtcx.Product.Remove(productItem);

 

Thx for your help,

Ozgur Aytekin

 

 

Answer 1

Use SingleOrDefault. It returns null if the row isn't found.

 

Anders

Answer 2

Thx Anders

 

 

Answer 3

I'm having the following problem with those two methods.

I have a record in db which has some numeric fields as height, lenght, width. For some reasons, when I call
MyContext.MyTable.SingleOrDefault(elem => elem.ID == ID) (ID is a given param in my method) it returns my entity , but those numeric fields have the value 0.

If I call MyContext.MyTable.Single(elem => elem.ID == ID) it brings me the entity with the correct values, but there is also the posibility that i don't have the specified ID and then it throws the exception with "Sequence has no elements".

I would like to use SingleOrDefault and still to get my values .. can anyone explain how to do it ?

Answer 4

The best way is to check whether the record exists or not by using the "Count" method.

int recCount = MyContext.MyTable.Count(elem => elem.ID == ID);

 

if (recCount > 0)

{

TableObject tblObject = (TableObject) MyContext.MyTable.SingleOrDefault(elem => elem.ID == ID)

....

....

}

 

Hope this helps (It did solve my problem).

 

Answer 5

Hi all,

I didn't understand Entity Framework. If everything is object why i couldn't reach all properties ???
Let me explain with an example.

 

Entities ctx = new Entities();

 

var postInfo = ctx.Posts.Where(p => p.IsOpenForUserQuestions).FirstOrDefault();

if

 

(postInfo != null)

{

 

string temp = string.Format("{0} {1} {2} <b>{3}</b><br />", postInfo.InterViewedDate, postInfo.Corporates.CorporateName, postInfo.JobTitles.Title, postInfo.PersonFullName);

ltrNextPost.Text = temp;

}

I am getting "object reference not set to an  instance of ... " error. But i get result from SQL belowed query.

SELECT Posts.PostID, Posts.PersonFullName, Posts.Url, Corporates.CorporateName, JobTitles.Title, Posts.InterViewedDate

FROM

 

Posts INNER JOIN

JobTitles

ON Posts.JobID = JobTitles.JobTitleID INNER JOIN

Corporates

ON Posts.CorporateID = Corporates.CorporateID

WHERE

 

(Posts.IsOpenForUserQuestions = 1)

OK. When i want to do that with join syntax in EF

 

 

 

 

var thepost = from post in ctx.Posts

 

                   join jobtitles in ctx.JobTitles on post.JobTitles

 

i can't because there is no JobTitleID property so i can't make a relation. It has a relation already that's why i see post.JobTitles insted of JobTitleID

What is the logic in EF?

Thanks in advance.

---

sometimes i feel my self like a "." that i am at end of an meaned sentences or begining of it.

Answer 6

Using SingleOrDefault works with LINQ to SQL but does not work with LINQ to Entities

Answer 7

I found that in LINQ To Entities (Entity Framework), that it is something similar
it's FirstOrDefault()

Answer 8

 FirstOrDefault()

Answer 9

You can also use : FirstOrDefault()

---

Prabhat Mohan

Answer 10

Worked for me. Many Thanks.