Self referencing loop from Newtonsoft JsonSerializer using Entity Framework Core

Question

I\'ve encountered the error:

JsonSerializationException: Self referencing loop detected for property \'Subject\' with type \'Project.Models.Subject

Answer 1

The problem of self-referencing loops during JSON serialization is connected to how EFCore loads related data (docs). When you load a collection, related entities may or may not be automatically populated depending on whether or not those object have been previously loaded. It's called automatic fix-up of navigation properties. Alternatively, they may be eagerly loaded via .Include().

Whenever you get a self-referencing graph of entities to be serialized, there are several options:

• Newtonsoft.Json.ReferenceLoopHandling.Ignore (officially recommended). It works but still can result in serializing excessive data if self-reference occurs deep in the hierarchy.

• [JsonIgnore] attribute on navigation properties. As you noted, attributes disappear when model classes are regenerated. Thus, their use can be inconvenient.

• (Best choice) Pre-select a subset of properties:

  var minimallyNecessarySet= _nwind.Products.Select(p => new {
      p.ProductID,
      p.ProductName,
      p.UnitPrice,
      p.CategoryID
  });
  
  return minimallyNecessarySet.ToList();
  

  This approach has the advantage of serializing only required data. It's compatible with DevExtreme's DataSourceLoader:

  return DataSourceLoader.Load(minimallyNecessarySet, loadOptions);