cannot save row update in LINQ

Question

I made a database of a school which contains a bunch of values and I'm trying to make an update function in the program I'm making , whenever I save the changes in the server it gives an Exception, here is a code sample of which how I update the row locally:

var query =
    from s in db.Students
    where s.StudentID == querierID
    select s;

foreach (Student s in query)
{
    s.FirstName = fntb.Text;
    s.LastName = lntb.Text;
    s.Mobile = mobiletb.Text;
    s.Street = streettb.Text;
}

And here is how I Actually save to the database(Send the updated row to it)

db.SaveChanges();

possible duplicate of [InvalidOperationException when calling SaveChanges in .NET Entity framework](http://stackoverflow.com/questions/1008582/invalidoperationexception-when-calling-savechanges-in-net-entity-framework) — Dave Zych, Sep 14 '15 at 21:03
No its not , in that question he makes a new row and saves it , though in this i update an already existing row. :D — GamerGamesGames, Sep 14 '15 at 21:05
There should be more details of the error if you 'view details' when the exception is thrown. We need to know that information too. — Brandon.Staley, Sep 14 '15 at 21:06
Additional information: The property 'StudentID' is part of the object's key information and cannot be modified. , though I'm not trying to modify StudentID because it is the primary key . :/ — GamerGamesGames, Sep 14 '15 at 21:08

score 1 · Answer 1 · answered Sep 14 '15 at 21:41

If StudentID is the primary key, you should write your code in a way that it will fail if this logic becomes false.

By using the Single() extension method your code will return just a single student or throw if the query returns more results.

This makes your code more readable

var studentToEdit = (
    from s in db.Students
    where s.StudentID == querierID
    select s
    ).Single();

studentToEdit.FirstName = fntb.Text;
studentToEdit.LastName = lntb.Text;
studentToEdit.Mobile = mobiletb.Text;
studentToEdit.Street = streettb.Text;

db.SaveChanges();

If you had used this approach, you would gotten a more detailed exception, pointing you in the right direction immedialtely.

Writing exactly what you mean, is the most difficult part of programming but has big advantages, like this.

score 0 · Answer 2 · answered Sep 14 '15 at 21:25

0

Okay , so I found the answer to it , the problem isn't actually what i thought it was , it is that when I Signed QueryID it was like

Selectedstudent.StudentID = QueryID

Instead of

QueryID = Selectedstudent.StudentID

I'm really sorry for wasting everyones time , but thank you all for trying to help me. and if anyone has a problem , they better check their code before posting a question and wasting everyones time like I did , really sorry everyone :( .

answered Sep 14 '15 at 21:25

GamerGamesGames

71
1
10

You can mark your own answer as correct answer if your problem is resolved with this solution. – Shilpa Soni Sep 15 '15 at 09:41
I have to wait 1 more day to do so :/ – GamerGamesGames Sep 15 '15 at 15:42

cannot save row update in LINQ

2 Answers2