Develop Reference

EF Core : build one-to-one relationship between two base classes

I have two base classes where each base class has inherited subclasses:
[Table("BaseClassOne")]
public class BaseClassOne
{
public Guid Id { get; set; }
public BaseClassTwo BaseTwo { get; set; }
}
[Table("DerivedClassOne")]
public class DerivedClassOne : BaseClassOne
{
public Guid Id { get; set; }
public string Name { get; set; }
}
[Table("BaseClassTwo")]
public class BaseClassTwo
{
public Guid Id { get; set; }
public BaseClassOne BaseOne { get; set; }
}
[Table("DerivedClassTwo")]
public class DerivedClassTwo : BaseClassTwo
{
public Guid Id { get; set; }
}
Now I would like to configure the relationships via model-builder, but without needing a discriminator:
builder
.Entity<BaseClassOne>()
.HasKey(b1 => b1.Id);
builder
.Entity<DerivedClassOne>()
.HasBaseType<BaseClassOne>();
builder
.Entity<BaseClassTwo>()
.HasKey(b2 => b2.Id);
builder
.Entity<DerivedClassTwo>()
.HasBaseType<BaseClassTwo>();
//This is where the problem starts:
builder
.Entity<BaseClassTwo>()
.HasOne(b2 => b2.BaseClassOne)
.WithOne(b1 => b1.BaseClassTwo)
.HasForeignKey<BaseClassTwo>(e => e.Id)
.OnDelete(Rule.Cascade);
I'm trying to run a query like following I get an error that the column m.Discriminator can't be found:
_context.BaseClassesTwo
.Select(b2 => new
{
val1 = b2.name,
val2 = b2.BaseClassOne.name
})
.ToList();
Is this an conceptional problem or do I need to change the configuration? And when, how?

Load navigation properties in generic repository

I have a problem when using AutoMapper and EF Core together to map navigation properties from the model to the DTO. My EF classes are:
public class Meal
{
public DateTime Day { get; set; }
public MealType MealType { get; set; }
public int MealId { get; set; }
}
public class MealType
{
public string Name { get; set; }
public int MealTypeId { get; set; }
}
And the corresponding DTO classes:
public class ExistingMealDto
{
public DateTime Day { get; set; }
public ExistingMealTypeDto MealType { get; set; }
public int MealId { get; set; }
public string MealTypeName { get; set; }
}
public class ExistingMealTypeDto
{
public string Name { get; set; }
public int MealTypeId { get; set; }
}
This is my AutoMapper mapping:
config.CreateMap<DataLayer.EfClasses.MealType, ExistingMealTypeDto>();
config.CreateMap<DataLayer.EfClasses.Meal, ExistingMealDto>()
.ForMember(x => x.MealType, x => x.MapFrom(x=>x.MealType))
.ForMember(x => x.MealTypeName, x => x.MapFrom(y => y.MealType.Name));
I'm loading the data within a generic method that looks like this:
public IEnumerable<TDtoOut> GetAllAsDto<TIn, TDtoOut>()
where TIn : class
{
var allEntities = DbContext.Set<TIn>();
return Mapper.Map<IEnumerable<TDtoOut>>(allEntities);
}
When calling this code, all Meal instances are loaded from the database and MealId and Day are filled correctly. However, MealType is null and therefore ExistingMealDto.MealType is null as well. I can work around this problem by explicitly calling DbContext.MealTypes.ToList(), but since the method should be generic for TIn, this is not a production solution.
How can I solve this issue? Thanks!

For getting the related data in generic method , you can judge the Type of the passed type. The following is a test demo , you could refer to:
public IEnumerable<TIn> GetAllAsDto<TIn>()
where TIn : class
{
Type typeParameterType = typeof(TIn);
if (typeParameterType == typeof(User))
{
var Entities = _context.Set<User>().Include(u=>u.Orders);
return (IEnumerable<TIn>)Entities;
}
else
{
var allEntities = _context.Set<TIn>();
return allEntities;
}
}
public void Test()
{
var data = GetAllAsDto<User>();
var data1 = GetAllAsDto<Status>();
}
Result

JsonException: A possible object cycle was detected which is not supported. This can either be due to a cycle or if the object depth is larger than

In my web API when I run project to get data from the database got this error
.net core 3.1
JsonException: A possible object cycle was detected which is not supported. This can either be due to a cycle or if the object depth is larger than the maximum allowed depth of 32.
These are my codes:
my Model
public class Product
{
public int Id { get; set; }
public string Name { get; set; }
public string ProductText { get; set; }
public int ProductCategoryId { get; set; }
[JsonIgnore]
public virtual ProductCategory ProductCategory { get; set; }
}
my productCategory class is:
public class ProductCategory
{
public int Id { get; set; }
public string Name { get; set; }
public string CatText { get; set; }
public string ImagePath { get; set; }
public int Priority { get; set; }
public int Viewd { get; set; }
public string Description { get; set; }
public bool Active { get; set; }
public DateTime CreateDate { get; set; }
public DateTime ModifyDate { get; set; }
public virtual ICollection<Product> Products { get; set; }
}
my repo is
public async Task<IList<Product>> GetAllProductAsync()
{
return await _context.Products.Include(p => p.ProductCategory).ToListAsync();
}
my interface
public interface IProductRepository
{
...
Task<IList<Product>> GetAllProductAsync();
...
}
and this is my controller in api project
[Route("api/[controller]")]
[ApiController]
public class ProductsController : ControllerBase
{
private readonly IProductRepository _productRepository;
public ProductsController(IProductRepository productRepository)
{
_productRepository = productRepository;
}
[HttpGet]
public ActionResult Get()
{
return Ok(_productRepository.GetAllProduct());
}
}
When I run API project and put this URL: https://localhost:44397/api/products
I got that error,
I can't resolve it

this is happening because your data have a reference loop.
e.g
// this example creates a reference loop
var p = new Product()
{
ProductCategory = new ProductCategory()
{ products = new List<Product>() }
};
p.ProductCategory.products.Add(p); // <- this create the loop
var x = JsonSerializer.Serialize(p); // A possible object cycle was detected ...
You can not handle the reference loop situation in the new System.Text.Json yet (netcore 3.1.1) unless you completely ignore a reference and its not a good idea always. (using [JsonIgnore] attribute)
but you have two options to fix this.
you can use Newtonsoft.Json in your project instead of System.Text.Json (i linked an article for you)
Download the System.Text.Json preview package version 5.0.0-alpha.1.20071.1 from dotnet5 gallery (through Visual Studio's NuGet client):
option 1 usage:
services.AddMvc()
.AddNewtonsoftJson(
options => {
options.SerializerSettings.ReferenceLoopHandling = ReferenceLoopHandling.Ignore;
});
// if you not using .AddMvc use these methods instead
//services.AddControllers().AddNewtonsoftJson(...);
//services.AddControllersWithViews().AddNewtonsoftJson(...);
//services.AddRazorPages().AddNewtonsoftJson(...);
option 2 usage:
// for manual serializer
var options = new JsonSerializerOptions
{
ReferenceHandling = ReferenceHandling.Preserve
};
string json = JsonSerializer.Serialize(objectWithLoops, options);
// -----------------------------------------
// for asp.net core 3.1 (globaly)
services.AddMvc()
.AddJsonOptions(o => {
o.JsonSerializerOptions
.ReferenceHandling = ReferenceHandling.Preserve
});
these serializers have ReferenceLoopHandling feature.
Edit : ReferenceHandling changed to ReferenceHandler in DotNet 5
but if you decide to just ignore one reference use [JsonIgnore] on one of these properties. but it causes null result on your API response for that field even when you don't have a reference loop.
public class Product
{
public int Id { get; set; }
public string Name { get; set; }
public string ProductText { get; set; }
public int ProductCategoryId { get; set; }
// [JsonIgnore] HERE or
public virtual ProductCategory ProductCategory { get; set; }
}
public class ProductCategory
{
public int Id { get; set; }
// [JsonIgnore] or HERE
public ICollection<Product> products {get;set;}
}

.NET 5 Web API
public static void ConfigureServices(this IServiceCollection services, IConfiguration configuration)
{
services.AddControllers()
.AddJsonOptions(o => o.JsonSerializerOptions
.ReferenceHandler = ReferenceHandler.Preserve);
}

I have the same issue, my fix was to add async and await keyword since I am calling an async method on my business logic.
Here is my original code:
[HttpGet]
public IActionResult Get()
{
//This is async method and I am not using await and async feature .NET which triggers the error
var results = _repository.GetAllDataAsync();
return Ok(results);
}
To this one:
HttpGet]
public async Task<IActionResult> Get()
{
var results = await _repository.GetAllDataAsync();
return Ok(results);
}

In .Net 6, you can use System.Text.Json to initialize a startup action with AddControllersWithViews like this in Program.cs,
using System.Text.Json.Serialization;
builder.Services.AddControllersWithViews()
.AddJsonOptions(x => x.JsonSerializerOptions.ReferenceHandler = ReferenceHandler.IgnoreCycles);
also you can use AddMvc like this,
builder.Services.AddMvc()
.AddJsonOptions(x => x.JsonSerializerOptions.ReferenceHandler = ReferenceHandler.IgnoreCycles);
but quote from Ryan
asp.net core 3.0+ template use these new
methodsAddControllersWithViews,AddRazorPages,AddControllers instead of
AddMvc.
I will recommend to use the first solution.

Ensure you have [JsonIgnore] on the correct fields to avoid a circular reference.
In this case you will need
public class Product
{
public int Id { get; set; }
public string Name { get; set; }
public string ProductText { get; set; }
[JsonIgnore]
public virtual ProductCategory ProductCategory { get; set; }
}
You probably don't need the ProductCategoryId field (depends if you are using EF and code first to define your DB)
Edit - In answer to noruk
There is often confusion in connected objects and navigation properties. You can get the data you want in JSON but also define the EF structures to get the correct DB structure (foreign keys, indexes, etc).
Take this simple example. A Product (for example a T-Shirt) has many sizes or SKUs (e.g. Small, Large, etc)
public class Product
{
[Key]
[MaxLength(50)]
public string Style { get; set; }
[MaxLength(255)]
public string Description { get; set; }
public List<Sku> Skus { get; set; }
}
public class Sku
{
[Key]
[MaxLength(50)]
public string Sku { get; set; }
[MaxLength(50)]
public string Barcode { get; set; }
public string Size { get; set; }
public decimal Price { get; set; }
// One to Many for Product
[JsonIgnore]
public Product Product { get; set; }
}
Here you can serialise a Product and the JSON data will include the SKUs. This is the normal way of doing things.
However if you serialise a SKU you will NOT get it's parent product. Including the navigation property will send you into the dreaded loop and throw the "object cycle was detected" error.
I know this is limiting in some use cases but I would suggest you follow this pattern and if you want the parent object available you fetch it separately based on the child.
var parent = dbContext.SKUs.Include(p => p.Product).First(s => s.Sku == "MY SKU").Product

I fixed my API Core Net6.0 adding [JsonIgnore]:
public class SubCategoryDto
{
public int Id { get; set; }
public string Name { get; set; }
public string Image { get; set; }
public int CategoryId { get; set; }
[JsonIgnore]
public Category Category { get; set; }
}

For net core 3.1 you have to add in Startup.cs:
services.AddMvc.AddJsonOptions(o => {
o.JsonSerializerOptions.ReferenceHandler = ReferenceHandler.Preserve;
o.JsonSerializerOptions.MaxDepth = 0;
})
and import at least this package using nuget.org include prerelease:
<PackageReference Include="System.Text.Json" Version="5.0.0-rc.1.20451.14" />

following code is working for me in dotnet 5.0 :
services.AddControllersWithViews()
.AddJsonOptions(o => o.JsonSerializerOptions
.ReferenceHandler = ReferenceHandler.Preserve);

Finally fixed mine with System.Text.Json not NewtonSoft.Json using
var options = new JsonSerializerOptions()
{
MaxDepth = 0,
IgnoreNullValues = true,
IgnoreReadOnlyProperties = true
};
Using options to serialize
objstr = JsonSerializer.Serialize(obj,options);

My project built with a similar error.
Here's the code before
public class PrimaryClass {
public int PrimaryClassId
public ICollection<DependentClass> DependentClasses { get; set; }
}
public class DependentClass {
public int DependentClassId { get; set; }
public int PrimaryClassId { get; set; }
public PrimaryClass primaryClass { get; set; }
}
I took away the PrimaryClass object from the DependentClass model.
Code after
public class PrimaryClass {
public int PrimaryClassId
public ICollection<DependentClass> DependentClasses { get; set; }
}
public class DependentClass {
public int DependentClassId { get; set; }
public int PrimaryClassId { get; set; }
}
I also had to adjust the OnModelCreating method from
modelBuilder.Entity<PrimaryClass>().HasMany(p => p.DependentClasses).WithOne(d => d.primaryClass).HasForeignKey(d => d.PrimaryClassId);
to
modelBuilder.Entity<PrimaryClass>().HasMany(p => p.DependentClasses);
The DbSet query that's running is
public async Task<List<DependentClass>> GetPrimaryClassDependentClasses(PrimaryClass p)
{
return await _dbContext.DependentClass.Where(dep => dep.PrimaryClassId == p.PrimaryClassId).ToListAsync();
}
The error could have been with any of these 3 sections of code, but removing the primary object reference from the dependent class and adjusting the OnModelCreating resolved the error, I'm just not sure why that would cause a cycle.

In my case the problem was when creating the entity relationships. I linked the main entity using a foreign key inside the dependent entity like this
[ForeignKey("category_id")]
public Device_Category Device_Category { get; set; }
also I referred the dipendend entity inside the main entity as well.
public List<Device> devices { get; set; }
which created a cycle.
Dependent Entity
public class Device
{
[Key]
public int id { get; set; }
public int asset_number { get; set; }
public string brand { get; set; }
public string model_name { get; set; }
public string model_no { get; set; }
public string serial_no { get; set; }
public string os { get; set; }
public string os_version { get; set; }
public string note { get; set; }
public bool shared { get; set; }
public int week_limit { get; set; }
public bool auto_acceptance { get; set; }
public bool booking_availability { get; set; }
public bool hide_device { get; set; }
public bool last_booked_id { get; set; }
//getting the relationships category 1 to many
public int category_id { get; set; }
[ForeignKey("category_id")]
public Device_Category Device_Category { get; set; }
public List<Booking> Bookings { get; set; }
}
Main Entity
public class Device_Category
{
public int id { get; set; }
public string name { get; set; }
public List<Device> devices { get; set; }
}
}
So I commented the
public List<Device> devices { get; set; }
inside main entity (Device_Category) and problem solved

Automapper configure 2 classes to one

I have the following DB (Infrastructure) classes:
[Table("ApplicationDriverEquipments")]
public partial class ApplicationDriverEquipment
{
public int Id { get; set; }
[StringLength(256)]
public string Make { get; set; }
[StringLength(256)]
public string Model { get; set; }
[StringLength(256)]
public string Year { get; set; }
[StringLength(256)]
public string VINNumber { get; set; }
[StringLength(256)]
public string PlateNumber { get; set; }
[StringLength(256)]
public string CurrentMileage { get; set; }
[StringLength(256)]
public string Length { get; set; }
public int TypeId { get; set; }
public virtual ApplicationDriverEquipmentType Type { get; set; }
public int DriverId { get; set; }
public virtual ApplicationDriver Driver { get; set; }
}
[Table("ApplicationDriverEquipmentTypes")]
public partial class ApplicationDriverEquipmentType
{
public ApplicationDriverEquipmentType()
{
Equipments = new HashSet<ApplicationDriverEquipment>();
}
public int Id { get; set; }
[Required]
[StringLength(256)]
public string Name { get; set; }
public virtual ICollection<ApplicationDriverEquipment> Equipments { get; set; }
}
and the following DTO (Domain) classes:
public abstract class ApplicationDriverEquipmentAbstractDomain
{
public int Id { get; set; }
public string Make { get; set; }
public string Model { get; set; }
public string Year { get; set; }
public string PlateNumber { get; set; }
public string CurrentMileage { get; set; }
public string Type { get; protected set; }
}
public class ApplicationDriverEquipmentTractorDomain : ApplicationDriverEquipmentAbstractDomain
{
public ApplicationDriverEquipmentTractorDomain()
{
Type = ApplicationDriverEquipmentTypeStaticStringsDomain.Tractor;
}
public string VINNumber { get; set; }
}
public class ApplicationDriverEquipmentTrailerDomain : ApplicationDriverEquipmentAbstractDomain
{
public ApplicationDriverEquipmentTrailerDomain()
{
Type = ApplicationDriverEquipmentTypeStaticStringsDomain.Trailer;
}
public string Length { get; set; }
}
public class ApplicationDriverEquipmentStraightTruckDomain : ApplicationDriverEquipmentAbstractDomain
{
public ApplicationDriverEquipmentStraightTruckDomain()
{
Type = ApplicationDriverEquipmentTypeStaticStringsDomain.StraightTruck;
}
public string VINNumber { get; set; }
public string Length { get; set; }
}
public class ApplicationDriverEquipmentCargoVanDomain : ApplicationDriverEquipmentAbstractDomain
{
public ApplicationDriverEquipmentCargoVanDomain()
{
Type = ApplicationDriverEquipmentTypeStaticStringsDomain.CargoVan;
}
public string VINNumber { get; set; }
public string Length { get; set; }
}
public static class ApplicationDriverEquipmentTypeStaticStringsDomain
{
public const string Tractor = "Tractor";
public const string Trailer = "Trailer";
public const string StraightTruck = "Straight Truck";
public const string CargoVan = "Cargo Van";
}
I wrote the following Automapper rules to resolve it:
CreateMap<Domain.POCO.Application.ApplicationDriverEquipmentTractorDomain, Infrastructure.Asset.ApplicationDriverEquipment>()
.ForMember(c => c.Type.Name, p => p.UseValue<string>(Domain.StaticStrings.ApplicationDriverEquipmentTypeStaticStringsDomain.Tractor));
CreateMap<Domain.POCO.Application.ApplicationDriverEquipmentTrailerDomain, Infrastructure.Asset.ApplicationDriverEquipment>()
.ForMember(c => c.Type.Name, p => p.UseValue<string>(Domain.StaticStrings.ApplicationDriverEquipmentTypeStaticStringsDomain.Trailer));
CreateMap<Domain.POCO.Application.ApplicationDriverEquipmentStraightTruckDomain, Infrastructure.Asset.ApplicationDriverEquipment>()
.ForMember(c => c.Type.Name, p => p.UseValue<string>(Domain.StaticStrings.ApplicationDriverEquipmentTypeStaticStringsDomain.StraightTruck));
CreateMap<Domain.POCO.Application.ApplicationDriverEquipmentCargoVanDomain, Infrastructure.Asset.ApplicationDriverEquipment>()
.ForMember(c => c.Type.Name, p => p.UseValue<string>(Domain.StaticStrings.ApplicationDriverEquipmentTypeStaticStringsDomain.CargoVan));
I got an error:
Expression 'c => c.Type.Name' must resolve to top-level member and not
any child object's properties. Use a custom resolver on the child type
or the AfterMap option instead.
UPDATE
I rewrote maps:
CreateMap<Domain.POCO.Application.ApplicationDriverEquipmentTractorDomain, Infrastructure.Asset.ApplicationDriverEquipment>()
.AfterMap((src, dest)=> dest.Type.Name = Domain.StaticStrings.ApplicationDriverEquipmentTypeStaticStringsDomain.Tractor);
CreateMap<Domain.POCO.Application.ApplicationDriverEquipmentTrailerDomain, Infrastructure.Asset.ApplicationDriverEquipment>()
.AfterMap((src, dest) => dest.Type.Name = Domain.StaticStrings.ApplicationDriverEquipmentTypeStaticStringsDomain.Trailer);
CreateMap<Domain.POCO.Application.ApplicationDriverEquipmentStraightTruckDomain, Infrastructure.Asset.ApplicationDriverEquipment>()
.AfterMap((src, dest) => dest.Type.Name = Domain.StaticStrings.ApplicationDriverEquipmentTypeStaticStringsDomain.StraightTruck);
CreateMap<Domain.POCO.Application.ApplicationDriverEquipmentCargoVanDomain, Infrastructure.Asset.ApplicationDriverEquipment>()
.AfterMap((src, dest) => dest.Type.Name = Domain.StaticStrings.ApplicationDriverEquipmentTypeStaticStringsDomain.CargoVan);
but now I got an error:
Type Map configuration: ApplicationDriverEquipmentTractorDomain ->
ApplicationDriverEquipment
Domain.POCO.Application.ApplicationDriverEquipmentTractorDomain ->
Infrastructure.Asset.ApplicationDriverEquipment
Property: Type ---> AutoMapper.AutoMapperMappingException: Missing
type map configuration or unsupported mapping.
Mapping types:
String -> ApplicationDriverEquipmentType
System.String -> Infrastructure.Asset.ApplicationDriverEquipmentType
Seems, I don't understand how to map it correctly

You are trying to map from
ApplicationDriverEquipmentTractorDomain.Type is a string
to
ApplicationDriverEquipment.Type is a ApplicationDriverEquipmentType
Where is your mapping configuration for that?
Is it even possible to map a string to a ApplicationDriverEquipmentType?
Sure, you can have a string Name, but where do you get the Id and Equipments?
I suspect you don't want to create a new instance of that type each time you map, but rather you need to look up an instance from some dictionary, sort of a registry pattern
To implement this idea, you simply need to
Load all of the ApplicationDriverEquipmentType from DB
Put them in a dictionary (assuming name is unique)
Register a custom type converter or custom value resolver as below
One way to implement this would be to use a custom type converter
You could use something like
void ConvertUsing(Func<TSource, TDestination> mappingFunction);
And put in your own function that would resolve your ApplicationDriverEquipmentType by name, assuming name is unique like this:
var applicationEquipments = new ApplicationDriverEquipmentTypeRepository().FindAll(); // get all the values somehow from db
var dictionary = applicationEquipments.ToDictionary(x=>x.Name);
Func<string, ApplicationDriverEquipmentType> resolver = x=>dictionary[x];
Yet another way to do this would be to use a custom value resolver
Essentially, the idea would be the same - map of pre-loaded objects, only the way you "plug it in" would be different

Try to use MapFrom method instead:
.ForMember(c => c.Type.Name, p => p.MapFrom(s => Domain.StaticStrings.ApplicationDriverEquipmentTypeStaticStringsDomain.Tractor));

Missing mapping configuration, classes mapped in profile

The profile:
public class StudentProfile : Profile
{
protected override void Configure()
{
Mapper.CreateMap<Student, StudentIndexModel>();
}
}
And the line it breaks on:
public ActionResult Index()
{
// Breaks here
var students = Mapper.Map<IEnumerable<StudentIndexModel>>(db.Students.ToList());
return View(students);
}
I'm getting an unsupported mapping exception when it gets records from the database. No exception when there are no records returned (the table has no records)
Error
Missing type map configuration or unsupported mapping.
Mapping types:
Student -> StudentIndexModel
ContosoUniversity.Models.Student -> ContosoUniversity.ViewModels.StudentIndexModel
Destination path:
IEnumerable`1[0]
The student class:
public class Student : Entity
{
public Student() { }
public string LastName { get; set; }
public string Forenames { get; set; }
public DateTime EnrolmentDate { get; set; }
public virtual ICollection<Enrolment> Enrolments { get; set; }
}
And the StudentIndexModel class:
public class StudentIndexModel
{
public int Id { get; set; }
public string LastName { get; set; }
public string Forenames { get; set; }
public DateTime EnrolmentDate { get; set; }
}
Where am I going wrong?

I've done it again, I find the answer to my own question 2 seconds later.
I added this to the Global.asax:
AutoMapperConfiguration.Configure();
Where AutomapperConfiguration has the Mapper.Initialize() method