C#•10mo ago

❔ Serializing related object EF

Hello all, I have 2 models

public class City {
    [Key]
    public int Id { get; set; }
    [Required]
    public string Name { get; set; }
    [Required]
    public string CountryName { get; set; }
    public Coordinates? Coordinates { get; set; }
}

public class Coordinates {
    public int Id { get; set; }
    public double X { get; set; }
    public double Y { get; set; }
    public int CityId { get; set; }
    public City City { get; set; } = null!;
}

public class City {
    [Key]
    public int Id { get; set; }
    [Required]
    public string Name { get; set; }
    [Required]
    public string CountryName { get; set; }
    public Coordinates? Coordinates { get; set; }
}

public class Coordinates {
    public int Id { get; set; }
    public double X { get; set; }
    public double Y { get; set; }
    public int CityId { get; set; }
    public City City { get; set; } = null!;
}

And I would like to include Coordinates of City in my response however I get error

JsonException: A possible object cycle was detected. This can either be due to a cycle or if the object depth is larger than the maximum allowed depth of 64

My query is

return db.Cities
        .Where(c => c.Name.ToLower().Contains(city.ToLower()))
        .Include(c => c.Coordinates)
        .ToList();

return db.Cities
        .Where(c => c.Name.ToLower().Contains(city.ToLower()))
        .Include(c => c.Coordinates)
        .ToList();

I have googled it and found different approaches but from the examples I saw, this should be working. Why does this happen?

28 Replies

Angius•10mo ago

Well, City references Coordinates and Coordinates reference the City So we do have an endless loop .Select() into a DTO instead of .Include()ing The same ringts true for all cases Even ones without cyclic dependencies

eysidi•10mo ago

I see, I got confused because every tutorial has a different approach of declaring relation

Angius•10mo ago

You could even flatten it too, since it's a 1:1 relationship If it's supposed to be a 1:1 relationship, then it's declared correctly

eysidi•10mo ago

Yes it is 1 to 1

Angius•10mo ago

What many tutorials fail at, however, is they all use .Include() instead of .Select()ing into DTOs

eysidi•10mo ago

so what am I supposed to do here? so, select?

Angius•10mo ago

Yes

return await db.Cities
        .Where(c => c.Name.ToLower().Contains(city.ToLower()))
        .Select(c => new CityDto {
            Name = c.Name,
            Country = c.CountryName
            X = c.Coordinates.X
            Y = c.Coordinates.Y
        })
        .ToListAsync();

return await db.Cities
        .Where(c => c.Name.ToLower().Contains(city.ToLower()))
        .Select(c => new CityDto {
            Name = c.Name,
            Country = c.CountryName
            X = c.Coordinates.X
            Y = c.Coordinates.Y
        })
        .ToListAsync();

for example

eysidi•10mo ago

there are some differences but even in official docs they use include

eysidi•10mo ago

https://learn.microsoft.com/en-us/aspnet/core/data/ef-mvc/read-related-data?view=aspnetcore-7.0

Tutorial: Read related data - ASP.NET MVC with EF Core

In this tutorial you'll read and display related data -- that is, data that the Entity Framework loads into navigation properties.

eysidi•10mo ago

not the same

public async Task<IActionResult> Index()
{
    var courses = _context.Courses
        .Include(c => c.Department)
        .AsNoTracking();
    return View(await courses.ToListAsync());
}

public async Task<IActionResult> Index()
{
    var courses = _context.Courses
        .Include(c => c.Department)
        .AsNoTracking();
    return View(await courses.ToListAsync());
}

from docs

Angius•10mo ago

Probably because it's a doc about loading related data While .Select() is a projection And it also loads related data

eysidi•10mo ago

meaning?

Angius•10mo ago

Well, a chapter in the math book about addition won't cover multiplication Even if 2 + 2 + 2 + 2 could be better represented as 2 * 4

eysidi•10mo ago

So Select is annotation?

Angius•10mo ago

huh? No?

eysidi•10mo ago

ah I see you are also flattening it as you said

Angius•10mo ago

It's a LINQ method that projects each element of an enumerable to a different thing

eysidi•10mo ago

what about without flattening?

Angius•10mo ago

return await db.Cities
        .Where(c => c.Name.ToLower().Contains(city.ToLower()))
        .Select(c => new CityDto {
            Name = c.Name,
            Country = c.CountryName,
            Coordinates = new CoordinatesDto {
                X = c.Coordinates.X,
                Y = c.Coordinates.Y
            }
        })
        .ToListAsync();

return await db.Cities
        .Where(c => c.Name.ToLower().Contains(city.ToLower()))
        .Select(c => new CityDto {
            Name = c.Name,
            Country = c.CountryName,
            Coordinates = new CoordinatesDto {
                X = c.Coordinates.X,
                Y = c.Coordinates.Y
            }
        })
        .ToListAsync();

eysidi•10mo ago

Preserve the nested structure?

Angius•10mo ago

Yep

eysidi•10mo ago

Yep that worked, What changes do I need to make my model so

return db.Cities
        .Where(c => c.Name.ToLower().Contains(city.ToLower()))
        .Include(c => c.Coordinates)
        .ToList();

return db.Cities
        .Where(c => c.Name.ToLower().Contains(city.ToLower()))
        .Include(c => c.Coordinates)
        .ToList();

this query works? Or is this wrong anyway?

Angius•10mo ago

I'm not sure it can work, because of the cyclic dependency You'd have to either remove the reference to city from coordinates Or the reference to coordinates from city

eysidi•10mo ago

I will try yes now it works I removed City from Coordinates I have seen some examples where related model is declared as virtual

public class City {
  ...
  public virtual Coordinates Coordinates { get; set; }
}

public class City {
  ...
  public virtual Coordinates Coordinates { get; set; }
}

What does virtual do in this case? Which one is correct?

Angius•10mo ago

It's for lazy loading Don't use lazy loading

eysidi•10mo ago

I see, thanks a lot for your help

Pobiega•10mo ago

Also, don't return your database entitites directly

Accord•10mo 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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❔ Serializing related object EF