object reference is not set to an instance of object

Mark Tabor

4y1.1k.NET

public JsonResult UpdateStudent(string FirstName,String LastName,string Gender)

{

StudentEntities MYDB=new StudentEntities();

var FindStudents=(from std in MYDB.students where studentId=id select std).FirstorDefault();

if(FindStudents==null)

{

Student mystudent=new Student();

FindStudents.FirstName=FirstName;

FindStudents.LastName=LastName

}

where running this above code I get exception as object reference is not set to an instance of object on the bold line

and my FindStudents variable is null from Linq query anyone can help

}

11 Replies

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Sachin Singh4y ago
Accepted answer
I guess you are trying to UpSert means update or Insert.
public JsonResult UpSertStudent(string FirstName,String LastName,string Gender)

{
int Id= Convert.ToInt32(TempData["Id"]); // just a guess
StudentEntities MYDB=new StudentEntities();

var student=MYDB.Students.Where(x.Id==Id).FirstorDefault();

if(student==null)

{

Student mystudent=new Student();

mystudent.FirstName=FirstName;

mystudent.LastName=LastName
MYDB.Students.Add(mystudent);

}else
{
student.FirstName=FirstName;

student.LastName=LastName;
MYDB.Entry(student).state=EntityState.Modified;

}
MYDB.SaveChanges();
Sachin Singh4y ago
Search Event Viewer (start-->type event viewer).
select Windows Logs--->Application

here you will get the recent stack trace for errors.
Mark Tabor4y ago
Hi Sachin I am not creating new object basically I have the object now it save the record when I am saving from postman but when my mobile application save it using the same method I use api it is still saying this error message
"validation failed for one or more entitites" see EntityValidationErrors property for more detail,
basically I have deployed the same code on IIS and my mobile app is using that API so how to debug the deployed version or how to find the issue ?
Mark Tabor4y ago
Thanks all and Sachin for valued feedback
Sachin Singh4y ago
yes, i checked, and the only problem i can see is it is null.
You need to check the DAL method, why is it returning null. If it can be null then you need to create its object, you can't assign anything to null.
Mark Tabor4y ago
Thanks sachin I checked and i shared the code with you its null and i am assiging it a value the code was working fine some time ago , can you check the code I shared
Sachin Singh4y ago
I guess
findCNICinLocalDB is null, when it is null it means you have no object, so you can't set its properties.
you again need to check whether it is null or not, if it is null then you need to create its object then only you can assign value.
Mark Tabor4y ago
Hi Sachin you got the point i have shared the entire code set with you and I am getting error on line
findCNICinLocalDB.BFORMNO=BFormNo;
Mark Tabor4y ago
I am assigning values only if the find student is null that is why I am assigin it the value with the paramters i am passing so the response or solution you are giving is not workable for me
Tim Harris4y ago
Looks likd FindStudents.FirstName should be mystudent.FirstName.
Muhammad Imran Ansari4y ago
FindStudents is null that's why FirstName is not accessible of null object. Try the following Linq query and make sure you are passing the correct id.

var FindStudents = ( from std in MYDB.students
where std.studentId = id
select std).FirstorDefault();