Blazor A second operation started on this context before a previous operation completed - asp.net-core

Question

I makes the NavMenu dynamically and return menu i the database by users and in the index page already i returned something in the database but when i run the application or reload it show me bellow error
InvalidOperationException: A second operation started on this context
before a previous operation completed. This is usually caused by
different threads using the same instance of DbContext. For more
information on how to avoid threading issues with DbContext, see
https://go.microsoft.com/fwlink/?linkid=2097913.
NavMenu code,
List<Menu> menus = new List<Menu>();
protected override async Task OnInitializedAsync()
{
menus = await MenuService.GetMenus();
}
Index code
#if (priorities == null)
{
<p><em>Loading...</em></p>
}
else
{
<table class="table">
<thead>
<tr>
<th>Name</th>
</tr>
</thead>
<tbody>
#foreach (var priority in priorities)
{
<tr>
<td>#priority.Name</td>
</tr>
}
</tbody>
</table>
}
#code {
List<Priority> priorities;
protected override async Task OnInitializedAsync()
{
priorities = await PriorityService.GetPriorities();
}
}

Answer 1

The solution is to use a `DbContextFactory :
Quoting docs:
Some application types (e.g. ASP.NET Core Blazor) use dependency injection but do not create a service scope that aligns with the desired DbContext lifetime. Even where such an alignment does exist, the application may need to perform multiple units-of-work within this scope. For example, multiple units-of-work within a single HTTP request.
In these cases, AddDbContextFactory can be used to register a factory for creation of DbContext instances. For example:
public void ConfigureServices(IServiceCollection services)
{
services.AddDbContextFactory<ApplicationDbContext>(
options =>
options.UseSqlServer(#"Server=(localdb)\mssqllocaldb;Database=Test"));
}

Answer 2

I got this error only when I attempted to access the user's information from the same service in multiple controls. Makes sense-- they are both fighting for the same resource on initialization.
For me, the solution wasn't to change the scope-- it was to re-think what I was really doing-- why have 2 separate controls trying to access Membership features for the same user at all?

Answer 3

My solution for a Blazor server app was to make the ApplicatonDbContext and the service both Transient:
services.AddDbContext<ApplicationDbContext>(x => x.UseSqlServer(connectionString), ServiceLifetime.Transient);
services.AddTransient<ICustomerService, CustomerService>();