Question

Each task has a reference to the goal it is assigned to. When I try and delete the tasks, and then the goal I get the error

“Store update, insert, or delete statement affected an unexpected number of rows (0). Entities may have been modified or deleted since entities were loaded. Refresh ObjectStateManager entries.” on the line _goalRepository.Delete(goalId);

What am I doing wrong?

 [HttpPost]
    public void DeleteGoal(int goalId, bool deleteTasks)
    {
        try
        {
            if (deleteTasks)
            {
                Goal goalWithTasks = _goalRepository.GetWithTasks(goalId);

                foreach (var task in goalWithTasks.Tasks)
                {
                    _taskRepository.Delete(task.Id);
                }
                goalWithTasks.Tasks = null;
                _goalRepository.Update(goalWithTasks);

            }

            _goalRepository.Delete(goalId);

        }
        catch (Exception ex)
        {
            Exception deleteException = ex;
        }
    }

Answer 1

Most likely the problem is because you’re attempting to hold onto and reuse a context across page views. You should create a new context, do your work, and dispose of the context atomically. It’s called the Unit Of Work pattern.

The main reason for this is that the context maintains some state information about the database rows it has seen, if that state information becomes stale or out of date then you get exceptions like this.

There are a lot of other reasons to use the Unit of Work pattern, I would suggest you do a web search and do a little reading as an educational exercise.