Fix duplicate JSON column in TPT child tables for complex types declared on base entity type

[Copilot]

In TPT inheritance, a complex property configured with .ToJson() on a base entity type incorrectly produced a JSON column in every child table in addition to the base table — causing duplicate schema and redundant data writes on insert.

modelBuilder.Entity<Person>()
    .UseTptMappingStrategy()
    .ComplexProperty(a => a.Address, b => b.ToJson());
// Bug: "Address" JSON column was created in both Person, Students, and Employees tables
// Fix: "Address" JSON column is created only in the Person (base) table

Root cause

RelationalModel.CreateTableMapping() iterated mappedType.GetComplexProperties(), which returns inherited properties. Scalar properties are filtered by GetColumnName(mappedTable) == null, but no equivalent filter existed for JSON-mapped complex properties, so the column was unconditionally created on every table in the hierarchy.

Changes

• RelationalModel.CreateTableMapping() — when processing complex properties for an entity type, skip any complex property whose declaring entity type maps to a different table (the base table in TPT). The check is bypassed for TPC, where each concrete table must contain all columns including inherited ones.
• RelationalModelTest — added Complex_property_json_column_is_not_duplicated_in_TPT_child_tables to assert the JSON column appears only in the base table for a TPT hierarchy.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>EF Core 11.0: Complex types and JSON Columns on Entity Types with TPT creates Duplicate JSON Column in Child Table</issue_title>
<issue_description>### Bug description

EF Core 11.0 introduced Complex types and JSON columns on entity types with TPT/TPC inheritance.

Expected

When using TPT, a JSON column is created in Child Table in addition to Parent table.

Actual

When using TPT, a JSON column created only in the Parent table.

Your code

Using EF Core 11,

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net11.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="11.0.0-preview.2.26159.112">
      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
      <PrivateAssets>all</PrivateAssets>
    </PackageReference>
    <PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="11.0.0-preview.2.26159.112" />
  </ItemGroup>

</Project>

Consider the following Db Context

using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Logging;
using System.ComponentModel.DataAnnotations.Schema;

using var context = new MyDbContext();

context.Database.EnsureDeleted();
context.Database.EnsureCreated();

await context.Students.AddRangeAsync(
    [
        new Student
        {
            Name = "John Doe",
            School = "School A",
            Address = new Address
            {
                AddressLine1 = "123 Main St",
                City = "Redmond",
                State = "WA"
            }
        }
    ]);


await context.Employees.AddRangeAsync(
    [
        new Employee
        {
            Name = "Jane Doe",
            Employer = "Employer A",
            Address = new Address
            {
                AddressLine1 = "456 Elm St",
                City = "Othertown",
                State = "NY"
            }
        }
    ]);

await context.SaveChangesAsync();

public abstract class Person
{
    public int Id { get; set; }

    public required string Name { get; init; }

    public required Address Address { get; set; }
}

public class Student : Person
{
    public required string School { get; set; }
}

public class Employee : Person
{
    public required string Employer { get; set; }
}

[ComplexType]
public class Address
{
    public required string AddressLine1 { get; set; }

    public required string City { get; set; }

    public required string State { get; set; }
}

public class MyDbContext : DbContext
{
    public DbSet<Student> Students { get; set; }

    public DbSet<Employee> Employees { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder
            .UseSqlServer(@"<ConnectionString>") //  Database compatibility level 170 (Microsoft SQL Server 2025)
            .LogTo(Console.WriteLine, LogLevel.Information);
    }

    override protected void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Person>()
            .UseTptMappingStrategy()
            .ComplexProperty(a => a.Address, b => b.ToJson());
    }
}

Stack traces

N/A

Verbose output

N/A

EF Core version

11.0.0-preview.2.26159.112

Database provider

Microsoft.EntityFrameworkCore.SqlServer

Target framework

.NET 11

Operating system

Windows 11

IDE

Visual Studio 2026 Insiders [11605.296]</issue_description>

Comments on the Issue (you are @copilot in this section)

@roji # AI Triage

The below is an AI-generated analysis and may contain inaccuracies.

Classification

Type: Bug
Areas: area-complex-types, area-model-building

Analysis

I was able to confirm a bug with complex types mapped to JSON via .ToJson() on a base entity type using TPT inheritance. The JSON column is incorrectly duplicated in child tables.

When running the reported scenario (tested on SQLite with EF 11.0 preview 2), the following table DDL is generated:

CREATE TABLE "Person" (
    "Id" INTEGER NOT NULL CONSTRAINT "PK_Person" PRIMARY KEY,
    "Name" TEXT NOT NULL,
    "Address" TEXT NOT NULL   -- correct: JSON column in base table
);

CREATE TABLE "Employees" (
    "Id" INTEGER NOT NULL CONSTRAINT "PK_Employees" PRIMARY KEY,
    "Employer" TEXT NOT NULL,
    "Address" TEXT NOT NULL,  -- BUG: duplicate JSON ...

</details>



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- Fixes dotnet/efcore#37937

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