C#•2mo ago

Deleting an entity with a many-to-many relationship throws an ArgumentNullException

I have a Memory and Person tables, with a junction table MemoryPerson that represents a many-to-many relationship between them The expected behaviour I want is to delete any related MemoryPerson whenever a Memory or Person is deleted. I have repositories for each entity, and they all follow the same general implementation:

    public async Task DeleteAsync(Memory entity)
    {
        _context.Memories.Remove(entity);
        await _context.SaveChangesAsync();
    }

    public async Task DeleteAsync(Memory entity)
    {
        _context.Memories.Remove(entity);
        await _context.SaveChangesAsync();
    }

That said, here comes my issue: When deleting a Person, all related MemoryPerson get deleted as expected, however when doing the same for Memory, an ArgumentNullException is thrown with the message Value cannot be null. (Parameter 'key'). The Call Stack points to that exact DeleteAsync method. I have checked and none of the values of the entity passed are null, I also tried adding checks in each of the methods but to no success. Does anyone have any idea of a possible solution? I'll send the OnConfiguring override in the replies due to character limit. A few extra details: - The entities are created properly - Deleting a memory without an existing MemoryPerson does not throw an exception - Deleting a memory with a MemoryPerson that does not relate to said memory does not throw an exception

27 Replies

GaxOP•2mo ago

It is currently configured this way: (I apologize for broken indentation)

modelBuilder.Entity<Person>(entity =>
{
    entity.HasKey(p => p.Id); // Primary key
    entity.Property(p => p.FullName).IsRequired().HasMaxLength(200);
    entity.Property(p => p.Bio).HasMaxLength(1000);
    entity.Property(p => p.ProfilePictureUrl).HasMaxLength(500);
    entity.Property(p => p.Birthday).HasColumnType("datetime");

    // Relationship with MemoryPerson
    entity.HasMany(p => p.MemoryPeople)
          .WithOne(mp => mp.Person)
          .HasForeignKey(mp => mp.PersonId)
          .OnDelete(DeleteBehavior.Cascade);
});

modelBuilder.Entity<Memory>(entity =>
{
    entity.HasKey(m => m.Id); // Primary key
    entity.Property(m => m.Title).IsRequired().HasMaxLength(200);
    entity.Property(m => m.Description).HasMaxLength(2000);
    entity.Property(m => m.Date).HasColumnType("datetime");

    // Relationship with MemoryPerson
    entity.HasMany(m => m.MemoryPeople)
          .WithOne(mp => mp.Memory)
          .HasForeignKey(mp => mp.MemoryId)
          .OnDelete(DeleteBehavior.Cascade);
});

        modelBuilder.Entity<MemoryPerson>(entity =>
        {
            entity.HasKey(mp => new { mp.MemoryId, mp.PersonId }); // Composite key

            // Relationship with Person
            entity.HasOne(mp => mp.Person)
                  .WithMany(p => p.MemoryPeople)
                  .HasForeignKey(mp => mp.PersonId);

            // Relationship with Memory
            entity.HasOne(mp => mp.Memory)
                  .WithMany(m => m.MemoryPeople)
                  .HasForeignKey(mp => mp.MemoryId);
        });

modelBuilder.Entity<Person>(entity =>
{
    entity.HasKey(p => p.Id); // Primary key
    entity.Property(p => p.FullName).IsRequired().HasMaxLength(200);
    entity.Property(p => p.Bio).HasMaxLength(1000);
    entity.Property(p => p.ProfilePictureUrl).HasMaxLength(500);
    entity.Property(p => p.Birthday).HasColumnType("datetime");

    // Relationship with MemoryPerson
    entity.HasMany(p => p.MemoryPeople)
          .WithOne(mp => mp.Person)
          .HasForeignKey(mp => mp.PersonId)
          .OnDelete(DeleteBehavior.Cascade);
});

modelBuilder.Entity<Memory>(entity =>
{
    entity.HasKey(m => m.Id); // Primary key
    entity.Property(m => m.Title).IsRequired().HasMaxLength(200);
    entity.Property(m => m.Description).HasMaxLength(2000);
    entity.Property(m => m.Date).HasColumnType("datetime");

    // Relationship with MemoryPerson
    entity.HasMany(m => m.MemoryPeople)
          .WithOne(mp => mp.Memory)
          .HasForeignKey(mp => mp.MemoryId)
          .OnDelete(DeleteBehavior.Cascade);
});

        modelBuilder.Entity<MemoryPerson>(entity =>
        {
            entity.HasKey(mp => new { mp.MemoryId, mp.PersonId }); // Composite key

            // Relationship with Person
            entity.HasOne(mp => mp.Person)
                  .WithMany(p => p.MemoryPeople)
                  .HasForeignKey(mp => mp.PersonId);

            // Relationship with Memory
            entity.HasOne(mp => mp.Memory)
                  .WithMany(m => m.MemoryPeople)
                  .HasForeignKey(mp => mp.MemoryId);
        });

A simple recreation for the problem is just

await personRepo.AddAsync(person);
await memoryRepo.AddAsync(memory);

var memoryPerson = new MemoryPerson
{
    MemoryId = memory.Id,
    PersonId = person.Id,
};

await memoryPersonRepo.AddAsync(memoryPerson);
await memoryRepo.DeleteAsync(memory);

await personRepo.AddAsync(person);
await memoryRepo.AddAsync(memory);

var memoryPerson = new MemoryPerson
{
    MemoryId = memory.Id,
    PersonId = person.Id,
};

await memoryPersonRepo.AddAsync(memoryPerson);
await memoryRepo.DeleteAsync(memory);

@yoajdin•2mo ago

Is this an issue with pasting? You're missing a ");" at the end below. Not sure if it will resolve your issue it's just the first thing that stepped out to me modelBuilder.Entity<Memory>(entity => { entity.HasKey(m => m.Id); // Primary key entity.Property(m => m.Title).IsRequired().HasMaxLength(200); entity.Property(m => m.Description).HasMaxLength(2000); entity.Property(m => m.Date).HasColumnType("datetime"); // Relationship with MemoryPerson entity.HasMany(m => m.MemoryPeople) .WithOne(mp => mp.Memory) .HasForeignKey(mp => mp.MemoryId) .OnDelete(DeleteBehavior.Cascade); }

GaxOP•2mo ago

yeah it was an issue with pasting, my bad the ); is present in the code, just was cut out when copying the source code

Present Chozo•2mo ago

Your problem is how you're declaring your MemoryPerson, I think. Try declaring it like this:

var memoryPerson = new MemoryPerson()
{
  Memory = memory,
  Person = person
};

var memoryPerson = new MemoryPerson()
{
  Memory = memory,
  Person = person
};

GaxOP•2mo ago

same error

Present Chozo•2mo ago

Do you have a stack trace? ...well, one you can publically share, I guess.

GaxOP•2mo ago

Unhandled exception. System.ArgumentNullException: Value cannot be null. (Parameter 'key')
   at System.Collections.Generic.Dictionary`2.FindValue(TKey key)
   at System.Collections.Generic.Dictionary`2.TryGetValue(TKey key, TValue& value)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.EntityReferenceMap.TryGet(Object entity, IEntityType entityType, InternalEntityEntry& entry, Boolean throwOnNonUniqueness)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.TryGetEntry(Object entity, IEntityType entityType, Boolean throwOnTypeMismatch)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.GetOrCreateEntry(Object entity, IEntityType entityType)
<a few more frames from EFCore related to detecting changes and delete>
at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChangesAsync(StateManager stateManager, Boolean acceptAllChangesOnSuccess, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.DbContext.SaveChangesAsync(Boolean acceptAllChangesOnSuccess, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.DbContext.SaveChangesAsync(Boolean acceptAllChangesOnSuccess, CancellationToken cancellationToken)
   at Meminisse.Application.Repositories.MemoryRepository.DeleteAsync(Memory entity) in C:\Users\<redacted>\source\repos\Meminisse\Meminisse.Application\Repositories\MemoryRepository.cs:line 30
   at Program.<Main>$(String[] args) in C:\Users\<redacted>\source\repos\Meminisse\Meminisse.TestApp\Program.cs:line 45
   at Program.<Main>(String[] args)

Unhandled exception. System.ArgumentNullException: Value cannot be null. (Parameter 'key')
   at System.Collections.Generic.Dictionary`2.FindValue(TKey key)
   at System.Collections.Generic.Dictionary`2.TryGetValue(TKey key, TValue& value)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.EntityReferenceMap.TryGet(Object entity, IEntityType entityType, InternalEntityEntry& entry, Boolean throwOnNonUniqueness)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.TryGetEntry(Object entity, IEntityType entityType, Boolean throwOnTypeMismatch)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.GetOrCreateEntry(Object entity, IEntityType entityType)
<a few more frames from EFCore related to detecting changes and delete>
at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChangesAsync(StateManager stateManager, Boolean acceptAllChangesOnSuccess, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.DbContext.SaveChangesAsync(Boolean acceptAllChangesOnSuccess, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.DbContext.SaveChangesAsync(Boolean acceptAllChangesOnSuccess, CancellationToken cancellationToken)
   at Meminisse.Application.Repositories.MemoryRepository.DeleteAsync(Memory entity) in C:\Users\<redacted>\source\repos\Meminisse\Meminisse.Application\Repositories\MemoryRepository.cs:line 30
   at Program.<Main>$(String[] args) in C:\Users\<redacted>\source\repos\Meminisse\Meminisse.TestApp\Program.cs:line 45
   at Program.<Main>(String[] args)

i cant send full stack trace due to character limit but i can probably put on a pastebin if needed

Present Chozo•2mo ago

Sure. But even from that excerpt it seems like something didn't save correctly.

GaxOP•2mo ago

i thought about that but everything is being added to the database correctly the memory, person and memoryperson are all saved in the database

Present Chozo•2mo ago

I'm guessing the Memory object also has its Id populated by the time you try and delete it, right?

GaxOP•2mo ago

yep

Present Chozo•2mo ago

And do you know for sure that your change tracker is tracking that entity when you try and delete it? Or I guess a better question is "Is the DbContext you're using to delete the entity the same one you used to add it?"

GaxOP•2mo ago

it is, yes

Present Chozo•2mo ago

Hmmm... If you're using a repo pattern, I assume you have a Get method, right?

GaxOP•2mo ago

i do

Present Chozo•2mo ago

Are you using FindAsync() or FirstOrDefault()?

GaxOP•2mo ago

FindAsync

Present Chozo•2mo ago

Try getting getting the most up-to-date instance of that Memory object prior to deleting it. If the change tracker is already tracking it, memory = await memoryRepo.GetAsync(memory.Id) shouldn't call the DB. See if that also throws an error.

GaxOP•2mo ago

same exception what bugs me is that whatever i do with Memory works perfectly with Person, they call the "same" methods (from their respective tables), have pretty much the same implementation and only one of them has this issue

Present Chozo•2mo ago

Maybe show both of the repo classes for both entities?

GaxOP•2mo ago

public class MemoryRepository : IRepository<Memory>
{
    private readonly MeminisseDbContext _context;

    public MemoryRepository(MeminisseDbContext context)
    {
        _context = context;
    }

    public async Task AddAsync(Memory entity)
    {
        await _context.Memories.AddAsync(entity);
        await _context.SaveChangesAsync();
    }

    public async Task AddRangeAsync(List<Memory> entities)
    {
        await _context.Memories.AddRangeAsync(entities);
        await _context.SaveChangesAsync();
    }

    public async Task DeleteAsync(Memory entity)
    {
        _context.Memories.Remove(entity);
        await _context.SaveChangesAsync();
    }

    public async Task DeleteAsync(Guid id)
    {
        var entity = await _context.Memories.FindAsync(id);
        if (entity != null)
        {
            _context.Memories.Remove(entity);
            await _context.SaveChangesAsync();
        }
    }

    public IQueryable<Memory> Get()
    {
        return _context.Memories.AsQueryable();
    }

    public async Task<List<Memory>> GetAllAsync()
    {
        return await _context.Memories.ToListAsync();
    }

    public async Task UpdateAsync(Memory entity)
    {
        _context.Memories.Update(entity);
        await _context.SaveChangesAsync();
    }
}

public class MemoryRepository : IRepository<Memory>
{
    private readonly MeminisseDbContext _context;

    public MemoryRepository(MeminisseDbContext context)
    {
        _context = context;
    }

    public async Task AddAsync(Memory entity)
    {
        await _context.Memories.AddAsync(entity);
        await _context.SaveChangesAsync();
    }

    public async Task AddRangeAsync(List<Memory> entities)
    {
        await _context.Memories.AddRangeAsync(entities);
        await _context.SaveChangesAsync();
    }

    public async Task DeleteAsync(Memory entity)
    {
        _context.Memories.Remove(entity);
        await _context.SaveChangesAsync();
    }

    public async Task DeleteAsync(Guid id)
    {
        var entity = await _context.Memories.FindAsync(id);
        if (entity != null)
        {
            _context.Memories.Remove(entity);
            await _context.SaveChangesAsync();
        }
    }

    public IQueryable<Memory> Get()
    {
        return _context.Memories.AsQueryable();
    }

    public async Task<List<Memory>> GetAllAsync()
    {
        return await _context.Memories.ToListAsync();
    }

    public async Task UpdateAsync(Memory entity)
    {
        _context.Memories.Update(entity);
        await _context.SaveChangesAsync();
    }
}

public class PersonRepository : IRepository<Person>
{
    private readonly MeminisseDbContext _context;

    public PersonRepository(MeminisseDbContext context)
    {
        _context = context;
    }

    public async Task AddAsync(Person entity)
    {
        await _context.People.AddAsync(entity);
        await _context.SaveChangesAsync();
    }

    public async Task AddRangeAsync(List<Person> entities)
    {
        await _context.People.AddRangeAsync(entities);
        await _context.SaveChangesAsync();
    }

    public async Task DeleteAsync(Person entity)
    {
        _context.People.Remove(entity);
        await _context.SaveChangesAsync();
    }

    public async Task DeleteAsync(Guid id)
    {
        var entity = await _context.People.FindAsync(id);
        if (entity != null)
        {
            _context.People.Remove(entity);
            await _context.SaveChangesAsync();
        }
    }

    public IQueryable<Person> Get()
    {
        return _context.People.AsQueryable();
    }

    public async Task<List<Person>> GetAllAsync()
    {
        return await _context.People.ToListAsync();
    }

    public async Task UpdateAsync(Person entity)
    {
        _context.People.Update(entity);
        await _context.SaveChangesAsync();
    }
}

public class PersonRepository : IRepository<Person>
{
    private readonly MeminisseDbContext _context;

    public PersonRepository(MeminisseDbContext context)
    {
        _context = context;
    }

    public async Task AddAsync(Person entity)
    {
        await _context.People.AddAsync(entity);
        await _context.SaveChangesAsync();
    }

    public async Task AddRangeAsync(List<Person> entities)
    {
        await _context.People.AddRangeAsync(entities);
        await _context.SaveChangesAsync();
    }

    public async Task DeleteAsync(Person entity)
    {
        _context.People.Remove(entity);
        await _context.SaveChangesAsync();
    }

    public async Task DeleteAsync(Guid id)
    {
        var entity = await _context.People.FindAsync(id);
        if (entity != null)
        {
            _context.People.Remove(entity);
            await _context.SaveChangesAsync();
        }
    }

    public IQueryable<Person> Get()
    {
        return _context.People.AsQueryable();
    }

    public async Task<List<Person>> GetAllAsync()
    {
        return await _context.People.ToListAsync();
    }

    public async Task UpdateAsync(Person entity)
    {
        _context.People.Update(entity);
        await _context.SaveChangesAsync();
    }
}

wait first one is wrong had some code that i was testing i updated it to the proper one

Present Chozo•2mo ago

Yeah, I'm stumped, unfortunately. I'd have to dig deeper into your code and DB to troubleshoot this.

GaxOP•2mo ago

its alright, thanks for trying anyways :)

asdf•2mo ago

Memory type already exists in the standard library so you might want to rename it

GaxOP•2mo ago

That is not the issue here though, but I get what you mean

hAssAnNaWaZi•5w ago

did you got it? @Gax

GaxOP•5w ago

sadly no at this point im considering rewriting it from scratch and see if a random change i didn't consider does it

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Deleting an entity with a many-to-many relationship throws an ArgumentNullException

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