C#•2y ago

✅ Collection appears to be null, even though it's not null on DB

I think the pictures already show the problem in more detail, there isn't much to it. User and Person have a many to many relationship, and that is all, I think... I don't have the slightest clue on why it says this. Would appreciate some help on this, tkss 😄

45 Replies

KooriByteOP•2y ago

The issue here is that I can't test if this user is already related to this person originally it was just user.People.Add(person), but at some point I added those person lines too for some reason

djmurp•2y ago

yes, .Include(x => x.People) in the code inside GetUserAsync. This is so that EF only gets from the DB what you ask for (otherwise it would write very inefficient SQL even if you only wanted a single field)

KooriByteOP•2y ago

oh, that is what he meant, I did not understand when he answered thank you a lot, will try it now I might be doing something wrong again is is suposed to be like this:

var user = _userManager.GetUserAsync(User.Include(x => x.People)).Result;

var user = _userManager.GetUserAsync(User.Include(x => x.People)).Result;

? forgot to correct ops in discord

djmurp•2y ago

do you own the method "GetUserAsync"? (can you edit it)

KooriByteOP•2y ago

nop, it is from Identity this is the only User property that VS says is null the rest of them are showing just fine (name, email, etc)

djmurp•2y ago

unfortunately you can't .Include the navigation property called .People then. So you will have to get the user from the _context itself some properties are fine because they are columns in the same user table, but it won't go and get related entities from a different table (like .People)

KooriByteOP•2y ago

I think I already done this, here

  public async Task<IActionResult> Details(int? id)
        {
            if (id == null || _context.People == null)
            {
                return NotFound();
            }

            var person = await _context.People
                .Include(x => x.ApplicationUsers)                
                .FirstOrDefaultAsync(m => m.Id == id);
            if (person == null)
            {
                return NotFound();
            }

            return View(person);
        }

  public async Task<IActionResult> Details(int? id)
        {
            if (id == null || _context.People == null)
            {
                return NotFound();
            }

            var person = await _context.People
                .Include(x => x.ApplicationUsers)                
                .FirstOrDefaultAsync(m => m.Id == id);
            if (person == null)
            {
                return NotFound();
            }

            return View(person);
        }

OOH i think I understood it know nah, I didn't :/

djmurp•2y ago

yep you've done the same thing, it's just that unfortunately you can't .Include that property when calling the built in Identity method - I thought you owned that code but you didn't do you know what table your users are in?

KooriByteOP•2y ago

in my db?

djmurp•2y ago

yeh, or the equivalent property name in your context

KooriByteOP•2y ago

users are in an ApplicationUser table, all "persons" are in a People table, and there is an intermediary table ApplicationUsersPeople between this two that have both the ApplicationUserId and PersonId for the many to many relationship I think that was the answer to your question, I'm not sure if I answered correctly, sorry :/

djmurp•2y ago

then you will have to query

var userWithPeople = _context.ApplicationUsers.Include(x => x.People).FirstOrDefault(x => x.Id == user.Id);

var userWithPeople = _context.ApplicationUsers.Include(x => x.People).FirstOrDefault(x => x.Id == user.Id);

or similar after the userManager.GetUserAsync(User) call

KooriByteOP•2y ago

and then I change user in the code bellow for userWithPeople afterwards? will try it, just a minute

djmurp•2y ago

yes that should work in a readable way I have another code recommendation but we can solve this first

KooriByteOP•2y ago

it said that the ApplicationUsers after _context was null I'll change it for _userManager, just a sec edit: this was just wrong

djmurp•2y ago

check this https://stackoverflow.com/questions/39837355/eager-loading-using-usermanager-with-ef-core, the answer for you actually in the question itself

KooriByteOP•2y ago

oh, thank you, I'll read it do you know if there is another approach for this? I still couldn't make it work

djmurp•2y ago

another approach would be entity framework lazy loading (in that case accessing .People will trigger additional SQL) but i'd avoid if possible - it's convenient but much less efficient! you can investigate it to see if it suits your use case, but feel free to persist and post an update instead

jcotton42•2y ago

you really do not want to use lazy loading in EF surprise, synchronous, network IO on a property access is a nasty surprise

KooriByteOP•2y ago

noooo, was half way into it already well, I think I'll try another solution this is way out of my current knowledge level, it's really frustrating sometimes

KooriByteOP•2y ago

is there a reason why only People is not working here?

jcotton42•2y ago

oh, is this asp.net identity?

KooriByteOP•2y ago

yep

jcotton42•2y ago

you might want to ask in #web or #database then

jcotton42•2y ago

this might also help https://learn.microsoft.com/en-us/ef/core/querying/related-data/explicit

Explicit Loading of Related Data - EF Core

Explicit loading of related data with Entity Framework Core

djmurp•2y ago

it's empty because you are going via userManager, something provided to you via Identity. It doesn't automatically know that you want all related data so it gives you the basics (column values). Anything more would result in a lot of SQL JOINs so the line below that line crashes?

jcotton42•2y ago

that's where explicit loading comes in it lets you load after the fact, without the foot bazooka of lazy loading

djmurp•2y ago

see above where I recommended the explicit loading

KooriByteOP•2y ago

the line bellow was the other attempt to correct this

var userWithPeople = _context.ApplicationUsers.Include(x => x.People).FirstOrDefault(x => x.Id == user.Id) ;

var userWithPeople = _context.ApplicationUsers.Include(x => x.People).FirstOrDefault(x => x.Id == user.Id) ;

it is like this ApplicationUsers was null

djmurp•2y ago

you cannot explicitly load a navigation property via the user manager GetUserAsync(User) method, so you have to do it alone via the _context hmm

KooriByteOP•2y ago

yes, this was in a link you sent previously. Problem was that I couldn't make it work too :c ApplicationUsers appeared null in this case

djmurp•2y ago

yeah ignore me. I am confusing @jcotton42 s responses by confusing eager loading with explicit loading, think ill go to sleep now.

jcotton42•2y ago

yeah the naming isn't very good classic microsoftism

djmurp•2y ago

so basically

var user = await _userManager.GetUserAsync(User);
_context.Entry(user) // lowercase user, NOT "User"!
        .Collection(b => b.People)
        .Load();

var user = await _userManager.GetUserAsync(User);
_context.Entry(user) // lowercase user, NOT "User"!
        .Collection(b => b.People)
        .Load();

KooriByteOP•2y ago

do I need to put .Result after .GetUserAsync(User)?

jcotton42•2y ago

no that's what the await is for

jcotton42•2y ago

also, looking at the docs, there's a LoadAsync https://learn.microsoft.com/en-us/dotnet/api/microsoft.entityframeworkcore.changetracking.collectionentry.loadasync?view=efcore-7.0#microsoft-entityframeworkcore-changetracking-collectionentry-loadasync(system-threading-cancellationtoken)

CollectionEntry.LoadAsync(CancellationToken) Method (Microsoft.Enti...

Loads entities referenced by this navigation property, unless IsLoaded is already set to true.

jcotton42•2y ago

might want that I'd still ask in #database and/or #web I doubt you're the first to run into this

KooriByteOP•2y ago

IT WORKED I used the .Result after, VS was screaming with me if I didn't use it

jcotton42•2y ago

no you want await foo not foo.Result using .Result makes it synchronous, and can result in deadlock

jcotton42•2y ago

https://blog.stephencleary.com/2012/07/dont-block-on-async-code.html

Don't Block on Async Code

This is a problem that is brought up repeatedly on the forums and Stack Overflow. I think it’s the most-asked question by async newcomers once they’ve learned the basics.

djmurp•2y ago

you need to change your controller method (FavoritePerson) to return Task<IActionResult> and add the async modifier or follow the suggestions VS givees

KooriByteOP•2y ago

if I take the Result off

_context.Entry(user)
                                                                .Collection(b => b.People)
                                                                .Load();

_context.Entry(user)
                                                                .Collection(b => b.People)
                                                                .Load();

stop working because b turns into a Task<ApplicationUser> I can put .Result after the user, but I think it makes it synchronous the same way

jcotton42•2y ago

@KooriByte that's why you await it

KooriByteOP•2y ago

oh, I'm sorry, I forgot to add the await Well, I'll close this. You both saved my day, thank you so much for helping 😄 I'll read the links you sent to understand this better

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✅ Collection appears to be null, even though it's not null on DB