Example of how to avoid multiple-thread access to DbContext in Blazor-Server

MyDbContext.cs

Instead of this

        return Db.Users.FirstOrDefaultAsync(x => x.EmailAddress == emailAddress);

do this

        return Db.InvokeAsync(() => ...the query above...);
        
        
// Add the following methods to your DbContext
        private SemaphoreSlim Semaphore { get; } = new SemaphoreSlim(1);

        public TResult Invoke<TResult>(Func<TResult> action)
        {
            Semaphore.Wait();
            try
            {
                return action();
            }
            finally
            {
                Semaphore.Release();
            }
        }

        public async Task<TResult> InvokeAsync<TResult>(Func<Task<TResult>> action)
        {
            await Semaphore.WaitAsync();
            try
            {
                return await action();
            }
            finally
            {
                Semaphore.Release();
            }
        }

        public Task InvokeAsync(Func<Task> action) =>
            InvokeAsync<object>(async () =>
            {
                await action();
                return null;
            });

        public void InvokeAsync(Action action) =>
            InvokeAsync(() =>
            {
                action();
                return Task.CompletedTask;
            });