C#•8mo ago

✅ EntityFramework: Navigation property makes a nested object call

So i have transports and categories models/tables , both are connected with a relationship , one category can have many transports and vice versa. Here is my code: Category model:

    public class Categories
    {
        [Key]
        public int category_id { get; set; }
        public string name { get; set; }
        // category can have many transports 
        public ICollection<Transports> Transports { get; set; }
    }

    public class Categories
    {
        [Key]
        public int category_id { get; set; }
        public string name { get; set; }
        // category can have many transports 
        public ICollection<Transports> Transports { get; set; }
    }

Transport model:

public class Transports
{
    [Key]
    public int transport_id { get; set; }
    public int category_id { get; set; }
    public Categories Category { get; set; }
    public string name { get; set; }
}

public class Transports
{
    [Key]
    public int transport_id { get; set; }
    public int category_id { get; set; }
    public Categories Category { get; set; }
    public string name { get; set; }
}

The problem is i get this schema in swagger api call:

  {
    "transport_id": 0,
    "category_id": 0,
    "categories": {
      "category_id": 0,
      "name": "string",
      "transports": [
        "string"
      ]
    },
    "name": "string"
}
]

  {
    "transport_id": 0,
    "category_id": 0,
    "categories": {
      "category_id": 0,
      "name": "string",
      "transports": [
        "string"
      ]
    },
    "name": "string"
}
]

My category table tries to call another value called "transports" , which i think is from the navigation property in categories model:

    "categories": {
      "category_id": 0,
      "name": "string",
      "transports": [
        "string"
      ]
    },

    "categories": {
      "category_id": 0,
      "name": "string",
      "transports": [
        "string"
      ]
    },

The problem fixes itself if i add [JsonIgnore] in my categories model above the navigation line:

       // category can have many transports 
        [JsonIgnore]
        public ICollection<Transports> Transports { get; set; }

       // category can have many transports 
        [JsonIgnore]
        public ICollection<Transports> Transports { get; set; }

but it seems this is a bad practice: I have tried to dto my Transport model:

    public class TransportsDto
    {
        public int transport_id { get; set }
        public int category_id { get; set; }
        public string name { get; set; }


    }

    public class TransportsDto
    {
        public int transport_id { get; set }
        public int category_id { get; set; }
        public string name { get; set; }


    }

but this way it does not return the relationships with category table. I am kinda lost here , what am i doing wrong?

3 Replies

Cosen•8mo ago

i am also using dto when returning a single category : (not sure if this even matters here)

    public class CategoriesDto
    {
        public int category_id { get; set; }

        public string name { get; set; }

    }

    public class CategoriesDto
    {
        public int category_id { get; set; }

        public string name { get; set; }

    }

Patrick•8mo ago

swagger shouldn't know about your EF models your DTOs are projections, the thing you want to expose to people using your software

public class CategoryDto
{
  public string Name { get; set; }
  public List<TransportDto> Transports { get; set; }
}

public class TransportDto
{
  public string Name { get; set; }
}

public class CategoryDto
{
  public string Name { get; set; }
  public List<TransportDto> Transports { get; set; }
}

public class TransportDto
{
  public string Name { get; set; }
}

var categories = await db.Categories
.Select(x => new CategoryDto
{
  Name = x.Name,
  Transports = x.Transports.Select(d => new TransportDto { Name = d.Name }).ToList();
})
.ToListAsync();

return categories;

var categories = await db.Categories
.Select(x => new CategoryDto
{
  Name = x.Name,
  Transports = x.Transports.Select(d => new TransportDto { Name = d.Name }).ToList();
})
.ToListAsync();

return categories;

Cosen•8mo ago

thanks this actually worked! I made changes to my transport dto and included

 public CategoriesDto categories { get; set; }

 public CategoriesDto categories { get; set; }

So my final transport dto is

    public class TransportsDto
    {
        public int transport_id { get; set }
        public int category_id { get; set; }
        public CategoriesDto categories { get; set; }
        public string name { get; set; }

    public class TransportsDto
    {
        public int transport_id { get; set }
        public int category_id { get; set; }
        public CategoriesDto categories { get; set; }
        public string name { get; set; }

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✅ EntityFramework: Navigation property makes a nested object call