Related entities in collection duplicate after inserting an object graph to database

Issue: after inserting a new entity, that contains another new related entities in its collection properties (one-to-many relationship), to a database - every related entity duplicates in the corresponding collection.

I’m using ABP 3.4.0, .net core 2.0, EF Core, Sql Server 2016 LocalDB.

Steps I took to reproduce an issue:

• Went to ABP Download Template page
• Chose following settings (I chose ‘Multi Page Web Application’, but I guess it doesn’t matter):

• Set connection string to Data Source=(localdb)\MSSQLLocalDB; Database=testABPDb; Trusted_Connection=True;
• Added two simplest entities to Core project:

public class ProductTest : Entity<int>
{
	public ProductTest()
	{
		ProductImages = new HashSet<ProductImageTest>();
	}

	[ForeignKey("ProductId")]
	public virtual ICollection<ProductImageTest> ProductImages { get; set; }
}

public class ProductImageTest : Entity<int>
{
	[ForeignKey(nameof(Product))]
	[Required]
	public int ProductId { get; set; }

	public virtual ProductTest Product { get; set; }
}

• Added them to DbContext:

public class testABPDbContext : AbpZeroDbContext<Tenant, Role, User, testABPDbContext>
{
	/* Define a DbSet for each entity of the application */

	public virtual DbSet<ProductTest> ProductTest { get; set; }

	public virtual DbSet<ProductImageTest> ProductImageTests { get; set; }

	public testABPDbContext(DbContextOptions<testABPDbContext> options)
		: base(options)
	{
	}
}

• Ran Add-Migration & Update-Database
• Added simplest AppService:

public class TestAppService : testABPAppServiceBase
{
	private readonly IRepository<ProductTest> _repo;
	public TestAppService(IRepository<ProductTest> repository)
		
	{
		_repo = repository;
	}

	public string Test()
	{
		var product = new ProductTest();
		product.ProductImages.Add(new ProductImageTest { Product = product });

		// inserting product to database (whether with InsertAndGetId() or Insert()) causes 
		// every related ProductImageTest in collection to duplicate, i.e. product.ProductImages.Count() doubles
		_repo.Insert(product); 
		
		return product.ProductImages.Count.ToString(); // returns 2
	}
}

• Launched Web.Host project, requested Test method() and got:

Although there is no duplication in the database (one record in ProductTest table and one in ProductImageTest table - as expected), Test() method returns 2 instead of 1, as there are two equivalent entities in product.ProductImages collection.

At first I thought there’s something wrong with my code, but I couldn’t find a bug at my end. I tested the same scenario without ABP (just pure EF Core, same entities) - and there was no duplication after inserting entities to database.

Am I missing something simple or is it a bug?

[douglasg14b]

I figured it out, it’s essentially this: https://github.com/aspnet/EntityFrameworkCore/issues/15687

[douglasg14b]

@luksfk I changed my GetHashCode to not use FK’s that may mutate and just compare by value, which works well for the aggregates I have.