ASPNET Core - Json response stops at the related model - json

Question

I have two classes that have relations between them. They are Market and Promotion classes. I'm facing a problem when I make a request. The json result stops when it comes to the relation.
The Market class:
public class Market : BaseModel
{
[Required]
public string Name { get; set; }
[Required]
public string Address { get; set; }
// GPS informations.
public double Latitude { get; set; }
public double Longitude { get; set; }
[Required]
public Guid PictureId { get; set; }
public Picture Picture { get; set; }
public List<Promotion> Promotions { get; set; }
}
The Promotion class:
public class Promotion : BaseModel
{
[Required]
public string Description { get; set; }
[Required]
public double Price { get; set; }
[Required]
public Guid PictureId { get; set; }
public Picture Picture { get; set; }
[Required]
public Guid MarketId { get; set; }
public Market Market { get; set; }
}
When I make the next request, I got an incomplete answer.
[HttpGet]
[AllowAnonymous]
public async Task<ActionResult<IEnumerable<Market>>> Get()
{
var markets = await _context.Markets
.Include(m => m.Owner)
.Include(m => m.Picture)
.Include(m => m.Promotions)
.ToListAsync();
return markets;
}
The response json stops when get at MarketId of the first promotion.
...
"pictureType": 0,
"pictureUrl": "https://superbarato.azurewebsites.net/api/Pictures/url/d6bc07a8-db55-4ee5-7342-08d73f6147e9",
"id": "d6bc07a8-db55-4ee5-7342-08d73f6147e9",
"createdAt": "2019-09-22T13:34:26.9367403",
"updatedAt": "0001-01-01T00:00:00",
"deletedAt": "0001-01-01T00:00:00",
"ownerId": "75c1f286-c07f-4e50-dda0-08d73f61058f",
"owner": null
},
"promotions": [
{
"description": "Açúcar Camil 1Kg",
"price": 5.0,
"pictureId": "e7af68b9-c053-4f4b-7344-08d73f6147e9",
"picture": null,
"marketId": "e2962be8-1a19-418a-6ce7-08d73f62308d"
How to get all the promotions?

Answer 1

In EF Core , you could configure Json.NET to ignore cycles that it finds in the object graph. This is done in the ConfigureServices(...) method in Startup.cs.
services.AddMvc()
.AddJsonOptions(
options => options.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore
);
Another alternative is to decorate one of the navigation properties with the [JsonIgnore] attribute, which instructs Json.NET to not traverse that navigation property while serializing.
Reference :https://learn.microsoft.com/en-us/ef/core/querying/related-data#related-data-and-serialization

Answer 2

The problem of yours is that Market and Promotion types/instances are referencing each other and you got into a cycle serializing those two indefinitely. You may solve it by projecting database model without relationship to response model/structure to avoid that.
[HttpGet]
[AllowAnonymous]
public async Task<ActionResult<IEnumerable<MarketModel>>> Get()
{
var markets = await _context.Markets
.Select(m => new MarketModel {
Name = m.Name,
// Other properties needed to be serialized to response body
Promotions = m.Promotions.Select(p => new PromotionModel {
Description = p.Description,
// Other properties needed to be serialized to response body
MarketId = p.Market.Id
}
}
.ToListAsync();
return markets;
}
public class MarketModel
{
public string Name { get; set; }
// Other properties needed to be serialized to response body
public List<PromotionModel> Promotions { get; set; }
}
public class PromotionModel
{
public string Description { get; set; }
// Other properties needed to be serialized to response body
public Guid MarketId { get; set; }
}
Hope it helps.