.NET Core 5 DbContext注入引发AggregateException与InvalidOperationException

问题场景 #

解决方案包含三个.NET Core 5项目：

• Demo.DAL（类库）：存放数据访问层代码，包含App_DbContext类
• Demo.BLL（类库）：业务逻辑层
• Demo.PL（MVC）：表现层，负责依赖注入配置

在Demo.PL的Startup中配置AddDbContext后，运行项目或执行数据库迁移时出现以下异常：

AggregateException: Some services are not able to be constructed (Error while validating the service descriptor 'ServiceType: Demo.DAL.Data.App_DbContext Lifetime: Scoped ImplementationType: Demo.DAL.Data.App_DbContext': Unable to resolve service for type 'Microsoft.EntityFrameworkCore.DbContextOptions`1[Microsoft.EntityFrameworkCore.DbContext]' while attempting to activate 'Demo.DAL.Data.App_DbContext'.)
Microsoft.Extensions.DependencyInjection.ServiceProvider..ctor(IEnumerable serviceDescriptors, IServiceProviderEngine engine, ServiceProviderOptions options)

InvalidOperationException: Error while validating the service descriptor 'ServiceType: Demo.DAL.Data.App_DbContext Lifetime: Scoped ImplementationType: Demo.DAL.Data.App_DbContext': Unable to resolve service for type 'Microsoft.EntityFrameworkCore.DbContextOptions`1[Microsoft.EntityFrameworkCore.DbContext]' while attempting to activate 'Demo.DAL.Data.App_DbContext'.
Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngine.ValidateService(ServiceDescriptor descriptor)

问题根源 #

App_DbContext的构造函数依赖的是DbContextOptions<DbContext>（基类泛型），但通过AddDbContext<App_DbContext>注册到DI容器的是DbContextOptions<App_DbContext>（当前类泛型），两者属于不同的服务类型，导致容器无法找到匹配的依赖项。

修复步骤 #

1. 修改Demo.DAL中的App_DbContext构造函数 #

将构造函数的泛型参数从DbContextOptions<DbContext>改为DbContextOptions<App_DbContext>，确保与注册的服务类型匹配：

namespace Demo.DAL.Data
{
    public class App_DbContext : DbContext
    {
        // 修正泛型参数为当前DbContext类型
        public App_DbContext(DbContextOptions<App_DbContext> options): base(options)
        {

        }
        public DbSet<Department> Departments { get; set; }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.ApplyConfigurationsFromAssembly(Assembly.GetExecutingAssembly());
        }
    }
}

2. 保留Demo.PL的Startup配置（无需修改） #

原有的AddDbContext配置是正确的，只需确保appsettings.json中已正确配置连接字符串myConnection：

public void ConfigureServices(IServiceCollection services)
{
    services.AddControllersWithViews();

    services.AddDbContext<App_DbContext>(optionsBuilder =>
    {
        optionsBuilder.UseSqlServer(Configuration.GetConnectionString("myConnection"));
    });
}

3. 重新执行数据库迁移（若需要） #

打开包管理器控制台，设置默认项目为Demo.DAL，依次执行以下命令：

Add-Migration InitialCreate
Update-Database

内容的提问来源于stack exchange，提问作者Hossam Zaki