I'm surprised that despite spending quite some time looking for the answer I haven't found it on the internet myself. What's even more surprising to me is that people tend to compare Attach to Add, and not to the Update. Furthermore, I've found very little mentions of the actual Update method, despite it being seemingly most obvious choice for the desired modify operation.
From the materials I managed to find I figured, that Attach should be used when you know the object exists somewhere in the database. If you don't make changes to it, no operations will be performed on the entity, and if you do - it will be updated. But then why would you need Update if it does the same thing from the sound of it?
I have this code snippet which I took from udemy course.
MovieController.cs
[HttpPut("{id}")]
public IActionResult ReplaceMovie(long id, [FromBody] Movie m)
{
if (ModelState.IsValid)
{
////
// logic in question starts here vvv
////
m.MovieId = id;
if (m.Studio != null && m.Studio.StudioId != 0)
{
context.Attach(m.Studio);
}
context.Update(m);
context.SaveChanges();
return Ok();
}
else
{
return BadRequest(ModelState);
}
}
But then why not just make it this way?
m.MovieId = id;
context.Update(m);
context.SaveChanges();
return Ok();
Would it not result in the same outcome, since we know that in case the Movie already has it's Studio assigned, then it (the Studio) exists in the database and we don't need to apply any changes to it?
Now if we applied some changes to the movie AND to the studio objects, then wouldn't it be safer to just perform the update modifications in their individual controllers? For example - if I want to update the movie and the studio, then I would first call the StudioController which would perform the modify operation on the Studio and then call the MovieController to update the movie.
What approach would be optimal for the best flexibility and clarity? What should I know about Attach and Update in general?
