❔ Ef core relations

WarningShoot · 2023-10-19T22:52:19.109Z

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.

W

WarningShootOP•10/19/23, 10:52 PM

it works when i do something like this

W

WarningShootOP•10/19/23, 10:52 PM

W

WarningShootOP•10/19/23, 10:53 PM

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

A

Angius•10/19/23, 11:05 PM

Delete that

.ToList()

.ToList()

.ToList()

.ToList()

A

Angius•10/19/23, 11:06 PM

And, yes, generally speaking using a

.Select()

.Select()

.Select()

.Select() is preferable to

.Include()

.Include()

.Include()

.Include()

W

WarningShootOP•10/19/23, 11:17 PM

i think u didnt understand me. ```cs

W

WarningShootOP•10/19/23, 11:17 PM

i would like to do something like this

W

WarningShootOP•10/19/23, 11:18 PM

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

foreach(var option in requestedQuestionnaire.Options)
{
  // do some stuff
}

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

foreach(var option in requestedQuestionnaire.Options)
{
  // do some stuff
}

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

foreach(var option in requestedQuestionnaire.Options)
{
  // do some stuff
}

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

foreach(var option in requestedQuestionnaire.Options)
{
  // do some stuff
}

W

WarningShootOP•10/19/23, 11:18 PM

i cant do that because options is null

A

Angius•10/19/23, 11:19 PM

You want just the options?

A

Angius•10/19/23, 11:19 PM

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);

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);

A

Angius•10/19/23, 11:20 PM

Bonus points if you make it async

W

WarningShootOP•10/19/23, 11:21 PM

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

A

Angius•10/19/23, 11:21 PM

Then you probably had lazy loading turned on

A

Angius•10/19/23, 11:21 PM

Which you shouldn't do

W

WarningShootOP•10/19/23, 11:23 PM

hmm maybe idk

A

Angius•10/19/23, 11:23 PM

Lazy loading queries the database each time a navigation property is accessed

A

Angius•10/19/23, 11:24 PM

Eager loading with

.Include()

.Include()

.Include()

.Include() or better yet,

.Select()

.Select()

.Select()

.Select(), only queries the database once and gets all the data

W

WarningShootOP•10/19/23, 11:24 PM

okay thanks

W

WarningShootOP•10/19/23, 11:25 PM

could you tell me how to do it with select?

A

Angius•10/19/23, 11:25 PM

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

A

Angius•10/19/23, 11:25 PM

And select into those

A

Angius•10/19/23, 11:28 PM

// 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" ]
// }

// 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" ]
// }

W

WarningShootOP•10/19/23, 11:29 PM

Big thanks for you

A

Accord•10/20/23, 11:38 PM

Was this issue resolved? If so, run

/close

/close

otherwise I will mark this as stale and this post will be archived until there is new activity.

❔ Ef core relations

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