update data using viewmodel

Question

I'm trying to update dataEntry using viewmodel and I'm getting this error msg :

Store update, insert, or delete statement affected an unexpected number of rows (0). Entities may have been modified or deleted since entities were loaded.

As far as I understand it's showing the ID is missing , but onDebug I can c the foreign id ( model.rgrade.SubjectId ) I cant finger out how to find the model rgradeId( in the results.

This is my code :

//checked if the subject name is allready in the db
var subjectNameQuery = db.Subject.Where(n => n.SubjectName.ToLower().Equals(model.sub.SubjectName));
if (subjectNameQuery.Count() > 0)
{
    //if the name is in the table, do Not add the name of the Id again
    model.rev.SubjectId = subjectNameQuery.SingleOrDefault().SubjectId;
    model.rgrade.SubjectId = subjectNameQuery.SingleOrDefault().SubjectId;
    if (model.rev.GBU == "Good")
    {
        model.rgrade.Good = +1;
    }
    else if (model.rev.GBU == "Bad")
    {
        model.rgrade.bad = +1;
    }
    else if (model.rev.GBU == "Ugly")
    {
        model.rgrade.Ugly = +1;
    }

    db.Entry(model.rgrade).State = EntityState.Modified;
}

Answer 1

You shouldn't need to set the state of the model. Also - you don't need to use SingleOrDefault when you know there will be at least one entity in the collection.

Also - did you mean to use = +1 ? This would set the value to 1, rather than increment it. If so, it's usually written = 1 .

If you did mean to increment it you should use += 1 .

Here's how I would have written it:

// Check if the subject name is already in the db.
var subjects = db.Subject.Where(s => s.SubjectName.Equals(model.sub.SubjectName, StringComparison.CurrentCultureIgnoreCase));

// If the name is in the table, do not add the name of the Id again.
if (subjects.Any())
{
    return;
}

var subjectId = subjects.First().Id;

model.rev.SubjectId = subjectId;
model.rgrade.SubjectId = subjectId;

if (model.rev.GBU == "Good")
{
     model.rgrade.Good = += 1;
}
else if (model.rev.GBU == "Bad")
{
    model.rgrade.bad = += 1;
}
else if (model.rev.GBU == "Ugly")
{
    model.rgrade.Ugly += 1;
}

// Save the entity (no need to set the state).