C# EF CF - Referential integrity constraint violation: Multiplue foreign keys to same table

Question

I'm having issues updating entities when referencing the same table multiple times in the one entity.

I have two Classes User and Expense. Expense is referencing to the User multiple times:

• User - Who lodged the Expense
• ApprovedUser - Who approved
• ProcessedUser - Who processed
• ModifiedUser - Who modified the Expense

    public class User
    {
        /// <summary>
        /// User Id
        /// </summary>
        [DatabaseGenerated(DatabaseGeneratedOption.None)]
        [Key]
        public string Id { get; set; }

        /// <summary>
        /// Display Name
        /// </summary>
        [Required]
        [Display(Name = "Display Name")]
        public string DisplayName { get; set; }
    }

    public class Expense
    {
        /// <summary>
        /// User Id
        /// </summary>
        [Required]
        [Display(Name = "User Id")]
        public string UserId { get; set; }

        /// <summary>
        /// Linked User
        /// </summary>
        [ForeignKey("UserId")]
        public User User { get; set; }

        /// <summary>
        /// Approved User Id
        /// </summary>
        [Display(Name = "Approved User Id")]
        public string ApprovedUserId { get; set; } = null;

        /// <summary>
        /// Linked Approve User
        /// </summary>
        [ForeignKey("ApprovedUserId")]
        public User ApprovedUser { get; set; }

        /// <summary>
        /// Processed User Id
        /// </summary>
        [Display(Name = "Processed User Id")]
        public string ProcessedUserId { get; set; } = null;

        /// <summary>
        /// Linked Processed User
        /// </summary>
        [ForeignKey("ProcessedUserId")]
        public User ProcessedUser { get; set; }

        /// <summary>
        /// Modified User Id
        /// </summary>
        [Display(Name = "Modified By User Id")]
        public string ModifiedByUserId { get; set; }

        /// <summary>
        /// Linked Modified User
        /// </summary>
        [ForeignKey("ModifiedByUserId")]
        public User ModifiedBy { get; set; }
    }

When i update the field ModifiedByUserId i get this: A referential integrity constraint violation occurred: The property value(s) of 'User.Id' on one end of a relationship do not match the property value(s) of 'Expense.ModifiedByUserId' on the other end.

However if i null the ModifiedByUserId it updates as normal. I have also tried to null the ModifiedBy and set the ModifiedByUserId with the same result.

I've looked at multiple SO posts and spent 12 hours trying to figure out what seems like something that should be so simple but i and can't find anything that's worked.

(I'd prefer to stay away from fluent api if possible.)

Example

Bob and Jim are in the User table and then there's a Expense Bod originally Modified the Expense so ModifiedByUserId is set to Bob's User.Id. I've now edited the Expense so the ModifiedByUserId should now be my User.Id. Nothing changes in the User, just the Expense

Generated SQL

create table [dbo].[Expense] (
    [Id] [int] not null identity,
    [SubmittedDate] [datetime2](7) not null,
    [UserId] [nvarchar](128) not null,
    [ApprovedUserId] [nvarchar](128) null,
    [ProcessedUserId] [nvarchar](128) null,
    [State] [int] not null,
    [ModifiedByUserId] [nvarchar](128) null,
    [LastNotification] [datetime2](7) not null,
    [NextNotification] [datetime2](7) not null,
    [NumberOfNotifications] [int] not null,
    [StopNotifications] [bit] not null,
    [Inserted] [datetime2](7) not null,
    [Updated] [datetime2](7) not null,
    [Deleted] [bit] not null,
    primary key ([Id])
);

create table [dbo].[User] (
    [Id] [nvarchar](128) not null,
    [DisplayName] [nvarchar](max) not null,
    [Department] [nvarchar](max) null,
    [JobTitle] [nvarchar](max) null,
    [Email] [nvarchar](max) not null,
    [TelephoneNumber] [nvarchar](max) null,
    [MobileNumber] [nvarchar](max) null,
    [DownloadedProfileImg] [bit] not null,
    [ManagerId] [nvarchar](128) null,
    [Deleted] [bit] not null,
    primary key ([Id])
);

alter table [dbo].[Expense] add constraint [Expense_ApprovedUser] foreign key ([ApprovedUserId]) references [dbo].[User]([Id]);
alter table [dbo].[Expense] add constraint [Expense_ModifiedBy] foreign key ([ModifiedByUserId]) references [dbo].[User]([Id]);
alter table [dbo].[Expense] add constraint [Expense_ProcessedUser] foreign key ([ProcessedUserId]) references [dbo].[User]([Id]);
alter table [dbo].[Expense] add constraint [Expense_User] foreign key ([UserId]) references [dbo].[User]([Id]);
alter table [dbo].[User] add constraint [User_Manager] foreign key ([ManagerId]) references [dbo].[User]([Id]);

Code

var expense = await ExpenseService.GetExpense(4);
expense.Updated = DateTime.Now;
expense.ModifiedByUserId = "user_id_string";
await ExpenseService.Update(expense);

GetExpense

        public async Task<Expense> GetExpense(int? id)
        {
            var expense = await Expenses.Query()
                .Include(x => x.User)
                .Include(x => x.ModifiedBy)
                .Include(x => x.ApprovedUser)
                .Include(x => x.ProcessedUser)
                .FirstAsync(x => x.Id == id);

            return expense;
        }

Update Expense:

        public async Task<Expense> Update(Expense expense)
        {
            Expenses.Update(expense);
            await Context.SaveAsync();

            return expense;
        }

Repository Update

        public void Update(TEntity entity)
        {
            _dbSet.Attach(entity);
            _context.SetState(entity, EntityState.Modified);
        }