Entity Framework Core throw DbUpdateConcurrencyException - entity-framework

Question

I am working on .net core entity framework. I have two list of class type. One for update and other for new entry, adding new records all worked fine but which is achieved by context.[Model].Add but update which is done by context.[Model].Update throw exception update i know no record been updated as it is running on local.
$exception {Microsoft.EntityFrameworkCore.DbUpdateConcurrencyException: Database operation expected to affect 1 row(s) but actually affected 0 row(s). Data may have been modified or deleted since entities were loaded.
Code
List<AnswerDataModel> surveyResponseListToCreate = new
List<AnswerDataModel>();
List<AnswerDataModel> surveyResponseListToUpdate = new
List<AnswerDataModel>();
if (surveyResponseListToUpdate.Count > 0)
{
foreach (var answerObject in surveyResponseListToUpdate)
{
Context.Answers.Update(answerObject);
if (answerObject.AnswerOptions.Count > 0)
{
foreach (var optItem in answerObject.AnswerOptions)
{
AnswerOptionDataModel answOpt = new AnswerOptionDataModel();
answOpt = optItem;
Context.AnswerOptions.Update(answOpt);
}
}
}
}
var recordsAffected = Context.SaveChanges();
if (!UsingExternalTransaction)
{
FinalizeTransaction(recordsAffected);
}

Answer 1

I can't resist a quote:
"I do not think [your code] means what you think it means."
Assuming that surveyResponseListToUpdate was a list of entities previously loaded and modified:
if (answerObject.AnswerOptions.Count > 0) // Unnecessary...
{
foreach (var optItem in answerObject.AnswerOptions)
{
AnswerOptionDataModel answOpt = new AnswerOptionDataModel(); // does nothing.
answOpt = optItem; // references existing answer option..
Context.AnswerOptions.Update(answOpt);
}
}
The whole block boils down to:
foreach (var optItem in answerObject.AnswerOptions)
Context.AnswerOptions.Update(optItem);
The error you are likely running into is because Update will recurse through navigation properties automatically, so when the parent (Answer) is updated, it's AnswerOptions will be updated as well. So when you go through the extra steps to try and save answer options, they've already been updated when the answer was saved. Provided the Answer was loaded by the same context that you are saving it to, you should be in the clear with:
foreach (var answerObject in surveyResponseListToUpdate)
Context.Answers.Update(answerObject);
var recordsAffected = Context.SaveChanges();
This should update the answer and it's associated answer objects. Even if options were added or removed, the change tracking should do it's job and ensure all of the associated data records are updated.
The extra if checks and such aren't necessary and just add to nesting depth making code harder to read.
However, I suspect that your real code is doing something different to the example given that my tests where I tried to reproduce your error, the code worked fine even updating the child references after updating the parent. If the above still raises issues, please update your example with the code you are running.