C#•14mo ago

❔ Ef core relations

Hey, im working on a simple project and im getting so much confused about how efcore works. I have two simple classes, where one have List of second one, and when i want to acces this list its always null.

14 Replies

WarningShootOP•14mo ago

it works when i do something like this

WarningShootOP•14mo ago

but i think its really bad if i need to do this

Angius•14mo ago

Delete that .ToList() And, yes, generally speaking using a .Select() is preferable to .Include()

WarningShootOP•14mo ago

i think u didnt understand me.

i would like to do something like this

i would like to do something like this

cs var requestedQuestionnaire = _context.Questionnaires .FirstOrDefault(x => x.Id == Id); foreach(var option in requestedQuestionnaire.Options) { // do some stuff } ``` i cant do that because options is null

Angius•14mo ago

You want just the options? If you want it all, you can still do

var requestedQuestionnaire = _context.Questionnaires
                .Include(x => x.Options)
                .FirstOrDefault(x => x.Id == Id);

var requestedQuestionnaire = _context.Questionnaires
                .Include(x => x.Options)
                .FirstOrDefault(x => x.Id == Id);

Bonus points if you make it async

WarningShootOP•14mo ago

yea i get it but i done it before and i didnt have to use Include()

Angius•14mo ago

Then you probably had lazy loading turned on Which you shouldn't do

WarningShootOP•14mo ago

hmm maybe idk

Angius•14mo ago

Lazy loading queries the database each time a navigation property is accessed Eager loading with .Include() or better yet, .Select(), only queries the database once and gets all the data

WarningShootOP•14mo ago

okay thanks ❤️ could you tell me how to do it with select?

Angius•14mo ago

You would create a new class, or multiple classes, that contain only the properties you need And select into those

// User has id, name, surname, date of birth
// Pet has id, name, breed
var user = await _context.Users
    .Where(u => u.Id == id)
    .Select(u => new UserDto { // class with only select properties
        Name = u.Name,
        PetNames = u.Pets.Select(p => p.Name)
    })
    .FirstOrDefaultAsync();
// result
// UserDto {
//     Name = "Bob",
//     PetNames = [ "Rex", "Caesar", "Fish McFishFace" ]
// }

// User has id, name, surname, date of birth
// Pet has id, name, breed
var user = await _context.Users
    .Where(u => u.Id == id)
    .Select(u => new UserDto { // class with only select properties
        Name = u.Name,
        PetNames = u.Pets.Select(p => p.Name)
    })
    .FirstOrDefaultAsync();
// result
// UserDto {
//     Name = "Bob",
//     PetNames = [ "Rex", "Caesar", "Fish McFishFace" ]
// }

WarningShootOP•14mo ago

Big thanks for you ❤️

Accord•14mo ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ Ef core relations