I am getting this error one of my projects.
InvalidOperationException: Sequence contains no elements.
here is my code in this I am trying to create auto-generated Id with string format.
public async Task<IActionResult> Create()
{
int id = _db.Patient.Max(item => item.Id)+1;
ViewBag.autoid = "BL0000"+id.ToString();
return View();
}
The max method will throw the InvalidOperation exception if the sequence contains no elements. - https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.max?view=netframework-4.8
You could use some extension methods like this - https://stackoverflow.com/a/18100382/38024
public static T MaxOrEmpty<T>(this IQueryable<T> query)
{
return query.DefaultIfEmpty().Max();
}
I resolved this issue
public async Task<IActionResult> Create()
{
//x = _db.Patient.Max(item => item.Id);
x=_db.Patient.DefaultIfEmpty().Max(item => item == null ? 1 : item.Id+1);
ViewBag.autoid = "BL0000"+x.ToString();
return View();
}
InvalidOperationException: Sequence contains no elements.
As the error message said,you do not have such elements in your Patient.So you need to judge whether it contains item or not.
Try this:
var data = _db.Patient.Select(item => item.Id);
if(data.Count()==0)
{
int id = 1;
}
else
{
int id = data.Max() + 1;
}
