Entity Framework Core: Database operation expected to affect 1 row(s) but actually affected 0 row(s) [duplicate] - entity-framework-core-2.1

Question

This question already has answers here:
Unable to edit db entries using EFCore, EntityState.Modified: "Database operation expected to affect 1 row(s) but actually affected 0 row(s)."
(17 answers)
Closed 2 years ago.
I am using Sql Server on Linux with EC Core (2.1.0-preview1-final)
I am trying to update some data coming from a web Api service (PUT) request. The data (ticket) is passed correctly and gets deserialised into an object (ticket).
When I try to update, I use the following code:
public Ticket UpdateTicket(Ticket ticket)
{
using (var ctx = new SupportTicketContext(_connectionString))
{
ctx.Entry(ticket).State = EntityState.Modified;
ctx.SaveChanges(); // <== **BLOWS UP HERE**
var result = ctx.Tickets
.First(t => t.TicketId == ticket.TicketId);
return result;
}
}
The code throws the following error:
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
I am able to Insert and fetch from the database, no problem.
If I restart Visual Studio, the error occurs usually on the second time I try to update ANY ticket (i.e. any other ticketId - it seems to be on the second and subsequent requests).
The updates are unpredictably successful! Sometimes I can update another ticket and it goes through (even on the 3rd or susequent request)
I have tried a number of modifications to the code, including
ctx.Attach(ticket);
but this does not help.
How do I get it to update the database successfully?
Any ideas on how to debug this? Logging seems to be difficult to set up.
Any ideas greatly appreciated.

Answer 1

There were two errors. First, I tried to call the Update() method without specifying a DbSet:
_applicationDbContext.Update(user);
Correct way:
_applicationDbContext.Users.Update(user);
The second error was trying to update a model that without first pulling it from the database:
public bool UpdateUser(IdentityUser model)
{
_applicationDbContext.Users.Update(model);
_applicationDbContext.SaveChanges();
return true;
}
Nope.
I first needed to retrieve it from the database, then update it:
public bool UpdateUser(IdentityUser model)
{
var user = _applicationDbContext.Users.FirstOrDefault(u => u.Id == model.Id);
user.PhoneNumberConfirmed = model.PhoneNumberConfirmed;
_applicationDbContext.Users.Update(user);
_applicationDbContext.SaveChanges();
return true;
}

Answer 2

Had such problem too, but the reason was a trigger I was using.
Changed the trigger type from "INSTEAD OF INSERT" to "AFTER INSERT" and instead of modifying and inserting the data I was allowing my command to insert the data to the table and then updated it using the trigger.