Set TPH discriminator value correctly when discriminator is part of the primary key

[lenraven]

I found a problem when I try to use the discriminator of a TPH mapping as part of primary key.

The Model what I want to map

public abstract class ProviderContract
{
    public Partner Partner { get; set; }
}

public class ProviderContract1 : ProviderContract
{
    // This is a specific type in the original model what is stored in JSON in the SQL
    public string Details { get; set; }
}

public class ProviderContract2 : ProviderContract
{
    // This is a specific type in the original model what is stored in JSON in the SQL
    public string Details { get; set; }
}

public class Partner
{
    public string Id { get; set; }
}

public class Provider
{
    public string Id { get; set; }
}

SQL schema

Table: [ProviderContracts]
Columns:

• [PartnerId]: FK to Partners table
• [ProviderId]: FK to Providers table and type discriminator
• [Details]: JSON serialized format of the Details property

PK: [PartnerId], [ProviderId]

DbContext

    public class SampleDbContext : DbContext
    {
        public DbSet<Partner> Partners => Set<Partner>();
        public DbSet<ProviderContract> ProviderContracts => Set<ProviderContract>();
        public DbSet<Provider> Providers => Set<Provider>();

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder.UseSqlServer(Program.ConnectionString);
            base.OnConfiguring(optionsBuilder);
        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Provider>().Property(p => p.Id).HasMaxLength(10).IsRequired().IsUnicode(false);
            modelBuilder.Entity<Provider>().HasData(new Provider {Id = "prov1"}, new Provider {Id = "prov2"});

            modelBuilder.Entity<Partner>().Property(p => p.Id).HasMaxLength(10).IsRequired().IsUnicode(false);
            modelBuilder.Entity<Partner>().HasData(new Partner { Id = "partner1" });

            var contractModelBuilder = modelBuilder.Entity<ProviderContract>();

            contractModelBuilder.HasOne(p => p.Partner).WithMany().IsRequired().HasForeignKey("PartnerId");
            contractModelBuilder.HasOne<Provider>().WithMany().IsRequired().HasForeignKey("ProviderId");
            contractModelBuilder.Property<string>("ProviderId").IsRequired().HasMaxLength(10).IsUnicode(false);
            
            contractModelBuilder.HasDiscriminator<string>("ProviderId")
                .HasValue<ProviderContract1>("prov1")
                .HasValue<ProviderContract2>("prov2");

            contractModelBuilder.HasKey("PartnerId", "ProviderId");

            modelBuilder.Entity<TfProviderContract>()
                        .HasBaseType<ProviderContract>()
                        .Property(p => p.Details).IsRequired().HasColumnName(nameof(ProviderContract1.Details));
            modelBuilder.Entity<WizzProviderContract>()
                        .HasBaseType<ProviderContract>()
                        .Property(p => p.Details).IsRequired().HasColumnName(nameof(ProviderContract2.Details));
        }
    }

Sample usage

    class Program
    {
        public static readonly string ConnectionString = "Server=.;Database=EfSamplePoc;Integrated Security=true;";

        static async Task Main()
        {
            await using var context = new SampleDbContext();

            var partner = await context.Partners.FirstAsync();

            context.ProviderContracts.Add(new ProviderContract1()
                {
                    Partner = partner,
                    Details = "Provider Contract Details"
                });

            await context.SaveChangesAsync();
        }
    }

When I run this program, the save changes will throw the following error:

Microsoft.EntityFrameworkCore.DbUpdateException: 'An error occurred while updating the entries. See the inner exception for details.'

Inner Exception:
SqlException: String or binary data would be truncated in table 'EfSamplePoc.dbo.ProviderContracts', column 'ProviderId'. Truncated value: 'ProviderCo'.
The statement has been terminated.

Stack trace:
   at Microsoft.EntityFrameworkCore.Update.ReaderModificationCommandBatch.<ExecuteAsync>d__29.MoveNext()
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at Microsoft.EntityFrameworkCore.Update.Internal.BatchExecutor.<ExecuteAsync>d__8.MoveNext()
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at Microsoft.EntityFrameworkCore.Update.Internal.BatchExecutor.<ExecuteAsync>d__8.MoveNext()
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.<SaveChangesAsync>d__97.MoveNext()
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.<SaveChangesAsync>d__101.MoveNext()
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at Microsoft.EntityFrameworkCore.SqlServer.Storage.Internal.SqlServerExecutionStrategy.<ExecuteAsync>d__7`2.MoveNext()
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at Microsoft.EntityFrameworkCore.DbContext.<SaveChangesAsync>d__54.MoveNext()
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at EFCoreSamples.Program.<Main>d__1.MoveNext() in C:\Source\Temp\EFCoreSamples\EFCoreSamples\Program.cs:line 49
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at EFCoreSamples.Program.<Main>d__1.MoveNext() in C:\Source\Temp\EFCoreSamples\EFCoreSamples\Program.cs:line 49
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
   at EFCoreSamples.Program.<Main>()

The problem is that the EF tries to execute the following SQL command:

Microsoft.EntityFrameworkCore.Database.Command: Error: Failed executing DbCommand (100ms)
[Parameters=[
    @p0='partner1' (Nullable = false) (Size = 10) (DbType = AnsiString),
    @p1='ProviderContract' (Nullable = false) (Size = -1) (DbType = AnsiString),
    @p2='Provider Contract Deatils' (Nullable = false) (Size = 4000)],
    CommandType='Text', CommandTimeout='30']

SET NOCOUNT ON;
INSERT INTO [ProviderContracts] ([PartnerId], [ProviderId], [Details])
VALUES (@p0, @p1, @p2);

Workaround

• Create a shadow property on ProviderContract: Id
• This Id property should be the PK
• Create a unique index for the following columns:
  • PartnerId
  • ProviderId

The modified DbContext

    public class SampleDbContext : DbContext
    {
        public DbSet<Partner> Partners => Set<Partner>();
        public DbSet<ProviderContract> ProviderContracts => Set<ProviderContract>();
        public DbSet<Provider> Providers => Set<Provider>();

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder.UseSqlServer(Program.ConnectionString);
            base.OnConfiguring(optionsBuilder);
        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Provider>().Property(p => p.Id).HasMaxLength(10).IsRequired().IsUnicode(false);
            modelBuilder.Entity<Provider>().HasData(new Provider {Id = "prov1"}, new Provider {Id = "prov2"});

            modelBuilder.Entity<Partner>().Property(p => p.Id).HasMaxLength(10).IsRequired().IsUnicode(false);
            modelBuilder.Entity<Partner>().HasData(new Partner { Id = "partner1" });

            var contractModelBuilder = modelBuilder.Entity<ProviderContract>();

            // Configure the shadow property
            contractModelBuilder.Property<int>("Id").IsRequired().UseIdentityColumn();

            contractModelBuilder.HasOne(p => p.Partner).WithMany().IsRequired().HasForeignKey("PartnerId");
            contractModelBuilder.HasOne<Provider>().WithMany().IsRequired().HasForeignKey("ProviderId");
            contractModelBuilder.Property<string>("ProviderId").IsRequired().HasMaxLength(10).IsUnicode(false);
            
            contractModelBuilder.HasDiscriminator<string>("ProviderId")
                .HasValue<ProviderContract1>("prov1")
                .HasValue<ProviderContract2>("prov2");

            // Create the unique index.
            contractModelBuilder.HasIndex("PartnerId", "ProviderId").HasName("UX_PartnerId_ProviderId").IsUnique();

            // Configure the shadow property as PK
            contractModelBuilder.HasKey("Id");

            modelBuilder.Entity<TfProviderContract>()
                        .HasBaseType<ProviderContract>()
                        .Property(p => p.Details).IsRequired().HasColumnName(nameof(ProviderContract1.Details));
            modelBuilder.Entity<WizzProviderContract>()
                        .HasBaseType<ProviderContract>()
                        .Property(p => p.Details).IsRequired().HasColumnName(nameof(ProviderContract2.Details));
        }
    }

When I made these changes on the mapping, the sample program works fine.

Further technical details

EF Core version: 3.1.3
Database provider: Microsoft.EntityFrameworkCore.SqlServer
Target framework: .NET Framework 4.7.2
Operating system: Windows 10
IDE: Visual Studio 2019 16.6.1

[ajcvickers]

Note for team: The reported exception is no longer thrown in EF Core 5.0. However, since the value is also on the dependent end of a relationship, we currently throw:

/home/ajcvickers/efcore/.dotnet/dotnet /home/ajcvickers/AllTogetherNow/Daily/bin/Debug/netcoreapp5.0/Daily.dll
Unhandled exception. System.InvalidOperationException: The value of 'ProviderContract1.ProviderId' is unknown when attempting to save changes. This is because the property is also part of a foreign key for which the principal entity in the relationship is not known.
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalEntityEntry.PrepareToSave()
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.GetEntriesToSave(Boolean cascadeChanges)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChangesAsync(DbContext _, Boolean acceptAllChangesOnSuccess, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.SqlServer.Storage.Internal.SqlServerExecutionStrategy.ExecuteAsync[TState,TResult](TState state, Func`4 operation, Func`4 verifySucceeded, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.DbContext.SaveChangesAsync(Boolean acceptAllChangesOnSuccess, CancellationToken cancellationToken)
   at Program.Main() in /home/ajcvickers/AllTogetherNow/Daily/Daily.cs:line 96
   at Program.Main() in /home/ajcvickers/AllTogetherNow/Daily/Daily.cs:line 96
   at Program.<Main>()

Process finished with exit code 134.

This might be fixable by changing the order of discriminator verses PK/FK initialization.

[ajcvickers]

Investigated this a bit more and it seems like the discriminator property is being incorrectly set to "ProviderContract". Explicitly setting to the correct value works:

var partner = await context.Partners.FirstAsync();
var contract = new ProviderContract1
{
    Partner = partner,
    Details = "Provider Contract Details"
};

context.Add(contract);
context.Entry(contract).Property("ProviderId").CurrentValue = "prov1";

Marking this as a bug.

[jotatoledo]

After migrating from 3.1 to 5.0 Im seeing a similar issue, under different conditions e.g. data model.