Circular dependency exception when switching values for unique index fields

[cjblomqvist]

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Question: Is it a bug? If not, how should one deal with below scenarios?

Scenario: I have a class (entity?) with 2 fields, and a unique index for those 2 fields. I have 2 instances of that class. I swap the values of one of the fields between the 2 instances, and try to save.

Actual outcome: EF Core exception "Unable to save changes because a circular dependency was detected in the data to be saved: ..."

Expected outcome: The data to be saved.

Context: SQL Server

Related issues: #29647 (and more along that thread) - but couldn't find any describing this specific scenario.

Include your code

Disclaimer: I haven't tested below code - but have something very similar in our codebase

[Index(nameof(A), nameof(B), IsUnique = true)]
public class Test {
	public string A { get; set; }
	public int B { get; set; }

	public Test(string a, int b) {
		A = a;
		B = b;
	}
}

var instance1 = new Test("A", 1);
var instance2 = new Test("B", 2);

context.SaveChanges(); // All good

instance1.B = 2;
instance1.A = 1;

context.SaveChanges(); // Exception

Include stack traces

Include the full exception message and stack trace for any exception you encounter.

Use triple-tick fences for stack traces. For example:

Unhandled exception. System.NullReferenceException: Object reference not set to an instance of an object.
   at SixFour.Sub() in C:\Stuff\AllTogetherNow\SixFour\SixFour.cs:line 49
   at SixFour.Main() in C:\Stuff\AllTogetherNow\SixFour\SixFour.cs:line 54

Include verbose output

ProductSupplier = Test
ProductId = A
Order = B

System.InvalidOperationException: Unable to save changes because a circular dependency was detected in the data to be saved: 'ProductSupplier [Modified] <-
Index { 'ProductId', 'Order' } ProductSupplier [Modified] <-
Index { 'ProductId', 'Order' } ProductSupplier [Modified]To show additional information call 'DbContextOptionsBuilder.EnableSensitiveDataLogging'.'.
   at Microsoft.EntityFrameworkCore.Utilities.Multigraph`2.ThrowCycle(List`1 cycle, Func`2 formatCycle, Func`2 formatException)
   at Microsoft.EntityFrameworkCore.Utilities.Multigraph`2.TopologicalSortCore(Boolean withBatching, Func`4 tryBreakEdge, Func`2 formatCycle, Func`2 formatException)
   at Microsoft.EntityFrameworkCore.Utilities.Multigraph`2.BatchingTopologicalSort(Func`4 tryBreakEdge, Func`2 formatCycle, Func`2 formatException)
   at Microsoft.EntityFrameworkCore.Update.Internal.CommandBatchPreparer.TopologicalSort(IEnumerable`1 commands)
   at Microsoft.EntityFrameworkCore.Update.Internal.CommandBatchPreparer.BatchCommands(IList`1 entries, IUpdateAdapter updateAdapter)+MoveNext()
   at Microsoft.EntityFrameworkCore.Update.Internal.BatchExecutor.ExecuteAsync(IEnumerable`1 commandBatches, IRelationalConnection connection, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChangesAsync(IList`1 entriesToSave, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChangesAsync(StateManager stateManager, 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 Microsoft.EntityFrameworkCore.DbContext.SaveChangesAsync(Boolean acceptAllChangesOnSuccess, CancellationToken cancellationToken)
   at API.Models.MainContext.SaveChangesAsync(CancellationToken cancellationToken) in <removed>Api\Models\MainContext.cs:line 981
   at API.Controllers.ProductController.UpdateSuppliers(Int32 productId, List`1 suppliersData) in <removed>Api\Controllers\ProductController.cs:line 1121
   at lambda_method6035(Closure, Object)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.AwaitableObjectResultExecutor.Execute(ActionContext actionContext, IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeActionMethodAsync>g__Awaited|12_0(ControllerActionInvoker invoker, ValueTask`1 actionResultValueTask)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeNextActionFilterAsync>g__Awaited|10_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeInnerFilterAsync>g__Awaited|13_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeFilterPipelineAsync>g__Awaited|20_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope)
   at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger)
   at API.Startup.<>c.<<Configure>b__14_2>d.MoveNext() in <removed>Api\Startup.cs:line 485

Include provider and version information

EF Core version: 7.0.4
Database provider: (e.g. Microsoft.EntityFrameworkCore.SqlServer)
Target framework: (e.g. .NET 7.0)
Operating system: Win 10 64 bit
IDE: (e.g. Visual Studio 2022 17.4.2)

[cjblomqvist]

I realize there's probably nothing you can do about this (even with just pure SQL this is challenging to handle). Solution for our case was to simply remove the index.

[0xced]

For our case, removing the index was not an option. We went with the following approach instead: within a transaction, delete the two rows, save, perform the modification, add the rows back, save.

var instance1 = new Test("A", 1);
var instance2 = new Test("B", 2);
context.SaveChanges();

using var transaction = context.Database.BeginTransaction();

context.Remove(instance1);
context.Remove(instance2);
context.SaveChanges();

instance1.B = 2;
instance1.A = 1;
context.Add(instance1);
context.Add(instance2);
context.SaveChanges();

transaction.Commit();