Blazor 在上一个操作完成之前在此上下文中启动了第二个操作

Question

我动态地制作了 NavMenu 并且 return 菜单由用户在数据库中并且在索引页面中我已经 return 在数据库中编辑了一些东西但是当我运行应用程序或重新加载它告诉我下面的错误

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.

导航菜单代码，

List<Menu> menus = new List<Menu>();

protected override async Task OnInitializedAsync()
{ 
    menus  = await MenuService.GetMenus();

}

索引码

@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

解决方案是使用`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

我对 Blazor 服务器应用程序的解决方案是使 ApplicatonDbContext 和服务都成为 Transient:

services.AddDbContext<ApplicationDbContext>(x => x.UseSqlServer(connectionString), ServiceLifetime.Transient);
services.AddTransient<ICustomerService, CustomerService>();

Answer 3

仅当我尝试从多个控件中的同一服务访问用户信息时才出现此错误。有道理——它们在初始化时都在争夺相同的资源。

对我来说，解决方案不是改变范围——而是重新思考我真正在做什么——为什么有 2 个单独的控件试图访问同一用户的会员功能？

Blazor 在上一个操作完成之前在此上下文中启动了第二个操作

Blazor A second operation started on this context before a previous operation completed

asp.net-core

blazor

blazor-server-side

blazor-client-side