EF Core TPC + Polymorphic API in .NET 8

🔥 Overview

This project showcases a production-grade implementation of EF Core's Table-Per-Concrete Type (TPC) mapping strategy combined with polymorphic API response handling using .NET 8's native JsonPolymorphic attribute and System.Text.Json.

⚡ Ideal for developers building complex domain models, versioned APIs, and clean serialization strategies for polymorphic data.

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📚 Table of Contents

• 🔥 Overview
• 🎯 Features
• 🧩 Sample Entities
• 🔁 Polymorphic Serialization with JsonPolymorphic
• 🔄 AutoMapper DTO Mapping
• 🔁 API Response Format
• 🛠️ Technologies
• 🚀 Running the Project
• 💡 Contributing

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🎯 Features

• ✅ Table-Per-Concrete (TPC) inheritance mapping using UseTpcMappingStrategy()
• 🔄 Polymorphic JSON serialization via native JsonPolymorphicAttribute
• 🧾 Custom ApiResponse<T> wrapper with conditional formatting
• 🔀 DTO mapping using AutoMapper for clean controller/service separation
• 🧪 Built-in sample data + Swagger UI

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🧩 Sample Entities

public abstract class RequestBase
{
    public Guid Id { get; set; }
    public DateTime CreatedAt { get; set; }
}

public class TypeARequest : RequestBase
{
    public string Param1 { get; set; }
    public int Param2 { get; set; }
}

public class TypeBRequest : RequestBase
{
    public bool Flag { get; set; }
    public decimal Amount { get; set; }
}

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🔁 Polymorphic Serialization with JsonPolymorphic

[JsonPolymorphic(TypeDiscriminatorPropertyName = "$type")]
[JsonDerivedType(typeof(TypeARequestDto), "typeA")]
[JsonDerivedType(typeof(TypeBRequestDto), "typeB")]
public abstract class RequestBaseDto { }

• Built-in support using System.Text.Json attributes
• Type information included for correct deserialization

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🔄 AutoMapper DTO Mapping

AutoMapper is used to transform entity models into polymorphic DTOs. It also supports inheritance with Include<> and bidirectional conversion with ReverseMap():

public class RequestMappingProfile : Profile
{
    public RequestMappingProfile()
    {
        CreateMap<RequestBase, RequestBaseDto>()
            .Include<TypeARequest, TypeARequestDto>()
            .Include<TypeBRequest, TypeBRequestDto>();

        CreateMap<TypeARequest, TypeARequestDto>().ReverseMap();
        CreateMap<TypeBRequest, TypeBRequestDto>().ReverseMap();
    }
}

Configuration is added in Program.cs:

builder.Services.AddAutoMapper(typeof(Program));

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🔁 API Response Format

{
  "success": true,
  "message": "Data fetched successfully",
  "data": {
    "$type": "typeA",
    "param1": "Sample",
    "param2": 42
  },
  "statusCode": 200,
  "dataTypeName": "TypeARequest"
}

• ApiResponse<T> includes both generic wrapper and runtime type info
• Compatible with Swagger and client libraries

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🛠️ Technologies

• .NET 8 Web API
• Entity Framework Core 8 (TPC Strategy)
• System.Text.Json with polymorphic attributes
• AutoMapper
• Swagger / Swashbuckle

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🚀 Running the Project

dotnet build
cd src/EfCoreTPC.Api
dotnet run

Visit https://localhost:<port>/swagger for API docs.

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💡 Contributing

Pull requests, bug fixes, and ideas welcome. Let’s push the boundaries of clean API design in .NET together.