具有Ninject和EF Core的MVC 5，上下文在一个查询后引发异常

Question

I am trying to use EF Core in our ASP.Net MVC 5 web application using Framework 4.6.1. We are using Ninject for dependency injection. I am injecting the Context in the DAL layer. I am successful a performing a single query but the context throws the following exception when the next query is run

No database provider has been configured for this DbContext. A provider can be configured by overriding the DbContext.OnConfiguring method or by using AddDbContext on the application service provider. If AddDbContext is used, then also ensure that your DbContext type accepts a DbContextOptions object in its constructor and passes it to the base constructor for DbContext.

I have seen this error before but I am not really sure how it applies in my situation. What is it about my setup that is causing this error to be thrown? Here is some code:

The Controller:

public ActionResult GetEnrollmentWorkflows()
{
    var class1Entities = this._class1Service.GetAll().ToList();
    var class1EntityIds = class1Entities.Select(x => x.Class1EntityId).ToList(); // Works
    var class2Entity =
        this._class2EntityService
            .GetByClass1EntityIds(class1EntityIds).ToList(); // Fails with exception
    return PartialView("_somePartial", model);
}

The context binding:

kernel.Bind<Context.ContextTenant>().ToSelf().InTransientScope()
    .WithConstructorArgument("options",
        new DbContextOptionsBuilder<Tables.ContextTenant>()
    .UseSqlServer(ConfigurationManager.ConnectionStrings
        [EnvironmentConsts.DbConnectionTenant].ConnectionString)
    .Options);

The context:

public ContextTenant(DbContextOptions<Tables.ContextTenant> options) : base(options)
{}

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
    base.OnConfiguring(optionsBuilder);
}

The Ninject Modules:

public class DalModule : NinjectModule
{
    public override void Load()
    {
        this.Kernel.Bind(x =>
            x.FromThisAssembly().SelectAllClasses().Join
                .FromAssemblyContaining<ISomeInterface>()
                .SelectAllInterfaces()
                .BindAllInterfaces().Configure(y => y.InTransientScope()));
    }
}



public class ServiceModule : NinjectModule
{
    public override void Load()
    {
        this.Kernel?.Load(new[] { new DalModule() });
        this.Kernel.Bind(x =>
            x.FromThisAssembly().SelectAllClasses().Join
                .FromAssemblyContaining<ISomeInterface>()
                .SelectAllInterfaces()
                .BindAllInterfaces().Configure(y => y.InTransientScope()));
    }
}

The DAL Classes

Class1:

public class Class1Repository : IClass1Repository
{
    private ContextTenant ContextTenant { get; }

    public Class1Repository(ContextTenant contextTenant)
    {
        ContextTenant = contextTenant;
    }

    public IEnumerable<Class1Entity> GetAll()
    {
        return this.ContextTenant.Class1Entity.Select(x => x);
    }
}

Class 2:

public class Class2Repository : IClass2Repository
{
    private readonly ContextTenant _contextTenant;

    public Class2Repository(ContextTenant contextTenant)
    {
        _contextTenant = contextTenant;
    }

    public IEnumerable<Class2Entity> GetByClass1EntityIds(
        IEnumerable<int> class1EntityIds)
    {
        return this._contextTenant.Class2Entity.Where(x =>
            class1EntityIds.Contains(x.Class1EntityId));
    }
}

The Services:

public class Class1Service : IClass1Service
{
    private readonly IClass1Repository _class1Repository;

    public Class1Service(IClass1Repository class1Repository)
    {
        _class1Repository = class1Repository;
    }

    public IEnumerable<Class1Entity> GetAll()
    {
        return this._class1Repository.GetAll();
    }
}

public class Class2Service : IClass2Service
{
    private readonly IClass2Repository _class2Repository;

    public Class2Service(IClass2Repository class2Repository)
    {
        _class2Repository = class2Repository;
    }

    public IEnumerable<Class2Entity> GetByClass1EntityIds(
        IEnumerable<int> class1EntityIds)
    {
        return this._class2Repository.GetByClass1EntityIds(class1EntityIds);
    }
}

Edit: Here is a little bit more code from the start up in case this would affect anything:

[assembly: WebActivatorEx.PreApplicationStartMethod(typeof(NinjectWebCommon), "Start")]
[assembly: WebActivatorEx.ApplicationShutdownMethod(typeof(NinjectWebCommon), "Stop")]
namespace MyApp
{
    public static class NinjectWebCommon
    {
        private static readonly Bootstrapper bootstrapper = new Bootstrapper();

        public static void Start()
        {
            DynamicModuleUtility.RegisterModule(typeof(OnePerRequestHttpModule));
            DynamicModuleUtility.RegisterModule(typeof(NinjectHttpModule));
            bootstrapper.Initialize(CreateKernel);
        }

        public static void Stop()
        {
            bootstrapper.ShutDown();
        }

        private static IKernel CreateKernel()
        {
            // Bind the context
        }
    }
}

Answer 1

Based on what I am reading above I believe it is because you are using RequestScope. The thing is that db context will dispose after each using and because you are still in the same request, when you call it again it has been disposed, but yet it serves that same instance. Change it to Transient (or Transient equivalent with Ninject, meaning get new db context on every request) and it should fix the problem.

Answer 2

I had similar problems in the past that sometimes could be solved by changing

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
    base.OnConfiguring(optionsBuilder);
}

In

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
    if (optionsBuilder.IsConfigured == false)
    { 
        base.OnConfiguring(optionsBuilder);
    }
}