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Transient and Scoped services consuming a singleton data source

I am trying to learn dependency inversion and IOC. In the process, I have hit a wall.
This is what I understand about DI principle -> high-level classes are based on abstractions and not implementations.
All good.
So keeping the above in mind. I have the following example.
public interface IServiceA
{
public void DoSomething();
}
public class ServiceA : IServiceAInterface
{
IDataInterface dataSource;
DataSourceType data;
// omitted config injectino for brevity
public ServiceA(IDataInterface _data)
{
dataSource = _dataSource;
var dataSourceName = config.GetValue<string>("DataSourceName");
data = dataSource.GetDataSource(dataSourceName);
}
public void doSomething()
{
data.doSomething();
}
}
public interface IDataInterface
{
public DataSourceType getDataSource(string ds);
}
public class DataAccessService : IDataInterface
{
public DataSourceType GetDataSource(string dataSource)
{
if (dataSource == "InApp")
{
var source = new DataSourceType();
return source;
}
else
{
return null;
}
}
}
The above is a service class which needs data to perform tasks which it gets from DataAccessService.
Now I am using an application class/model for persistence throughout the app lifetime. Therefore I have registered it as a singleton.
Startup.cs
public void ConfigureServices(IServiceCollection services)
{
---
services.AddSingelton<IDataInterface,DataAccessService>();
service.AddScoped<IServieAInterface,ServiceA>();
---
}
This does not work.
I hypothesize it is because, the parent service (service A) has a lesser lifetime than the child service (DataAccessService).
I have understood through this that service A is responsible for instantiation of the object.
However, I expected the IOC container to instantiate only one DataAccessService object and inject it to all services that need this.
Not sure why my assumption is wrong.
Based on the above hypothesis I tried the following:
public interface IDataInterface
{
}
public class DataAccessService : IDataInterface
{
public DataSourceType dataSource;
public DataAccessService(string ds)
{
if (ds == "InApp")
{
this.dataSource = new DataSourceType();
}
else
{
this.dataSource = null;
}
}
}
public class ServiceA: DataAccessService,IServceAInterface
{
DatSourceTye data;
public ServiceA():base("InApp")
{
config = _config;
data = dataSource;
}
public void doSomething()
{
data.doSomething();
}
}
Startup.cs
// Hoping to pass parameter through startup
services.AddSingleton<IDataInterface>(x =>
ActivatorUtilities.CreateInstance<DataAccessService>(x, "InApp")
);
service.AddScoped<IServieAInterface,ServiceA>();
I hoped the above would work, as here the DataAccessService is responsible for initialization.
But still a new DataAccessService object is created for every class.
I think, I have messed up my understanding about how the life times work.
need help on this.
Also, what I am trying to achieve is a singleton data source on which different services act on throughout the application lifetime.
Transient and scoped services consuming a singleton data source. I think this should be possible
Is there something bad in terms of design in what I am trying to achieve?

public DataAccessService(string ds)
{
if (ds == "InApp")
{
this.dataSource = new DataSourceType();
}
else
{
this.dataSource = null;
}
}
This method in the data service was being called every time, I needed the data source.
As this method is instantiating another class manually, though the service is singleton,
every time the above method - DataAccessService was called , I was getting a new instance.

Dependency Injection of DbContext with Dynamic ConnString

Below is a simple but functional example of roughly how I would do Dependency Injection. This works great when my DbContext connection string is not dynamic. Even if it's passed in to the factory through a config file or whatever, it doesn't matter so long as it's the same one all the time.
What I need is to wrap my head around how to make (ideally minor) modifications to the below code to allow for the connection string to be determined dynamically at run time.
For example, say on the View the user was able to not only select the teacher to be passed into the Post method of the controller, but also the school. If, for simplicity sake, there are 2 schools that have the exact same database structure, but have different connection strings how do I get that down from the controller to the factory?
I've experimented with passing a value from method to method, but this isn't really sustainable for large projects, increases the likelihood of errors and overall is just messy (besides violations of SOLID) to be passing something from layer to layer like that. (If desired I can add the not exactly ideal attempts I've made, I've omitted them for brevity sake since this is already a fairly long question what with the code examples and all).
Controller
public class HomeController : Controller
{
private readonly IDataService _dataService;
public HomeController(IDataService dataService)
{
_dataService = dataService;
}
public ActionResult Index()
{
var results = _dataService.GetTeachers();
var model = new ViewModel
{
Teachers = results
};
return View(model);
}
[HttpPost]
public ActionResult Index(ViewModel model)
{
var results = _dataService.GetCourses(model.Teacher);
model.Courses = new List<string>(results);
return View(model);
}
}
Service
public class DataService : IDataService
{
private readonly IDataRepo _dataRepo;
public DataService(IDataRepo dataRepo)
{
_dataRepo = dataRepo;
}
public List<string> GetCourses(string teacherName)
{
return _dataRepo.GetCourses()
.Where(c => c.Teacher.FirstName == teacherName)
.Select(c => c.Name)
.ToList();
}
public List<string> GetTeachers()
{
return _dataRepo.GetCourses()
.Select(c => c.Teacher.FirstName)
.ToList();
}
}
Repository
public class DataRepo : IDataRepo
{
private readonly SchoolContext _context;
public DataRepo()
{
_context = ContextFactory.MakeContext();
}
public IEnumerable<Course> GetCourses()
{
return _context.Courses;
}
}
Context Factory
public static class ContextFactory
{
public static SchoolContext MakeContext()
{
var connString =
"connStringA";
return new SchoolContext(connString);
}
}
UnityConfig
public static void RegisterComponents()
{
var container = new UnityContainer();
container.RegisterType<IDataService, DataService>();
container.RegisterType<IDataRepo, DataRepo>();
DependencyResolver.SetResolver(new UnityDependencyResolver(container));
}

First, you have to decide how are you going to get the current connection string to use. Is it through a URL? or using the current user or whatever other way.
Then, create another database that has a mapping between the connection strings and the method you chose (user, url ...)
Lastly, implement a way to get the record from the database.
so, assuming that you will use the URL as an identifier for the current tenant, your entity class should be like this:
public class Tenant
{
public string Url {get;set;}
public string ConnectionString {get;set;}
}
An interface that represents the logic to get the current tenant:
public interface ICurrentTenantService
{
Tenant GetCurrentTenant();
}
And now you will put its implementation
public class CurrentTenantService : ICurrentTenantService
{
public Tenant GetCurrentTenant()
{
string currentUrl = HttpContext.Current.Url; //make sure to get only the base URL here
return TenantDbContext.Tenants.FirstOrDefault(t=>t.Url == url); //TenantDbContext should be a class that has the Tenant entity
}
}
Now you have to wire up the context factory to the tenant service like this
public static class ContextFactory
{
private readonly ICurrentTenantService currentTenantService;
//Inject it in the constructor
public static SchoolContext MakeContext()
{
var currentTenant= currentTenantService.GetCurrentTenant(); //Check for NULL
return new SchoolContext(currentTenant.ConnectionString);
}
}

Mocking static method options

I understand that you can't mock a static method with moq, but I was wondering what my possible options are
I have a controller class defined
public class CustomerController : BaseController
{
private ICustomerManager cm;
public CustomerController()
: this(new CustomerManager())
{
}
public CustomerController(ICustomerManager customerMan)
{
cm = customerMan;
}
public ActionResult EditContact(ContactVM model, IEnumerable<HttpPostedFileBase> Files, PageAction pageAction)
{
if (ModelState.IsValid)
{
InitializeContactVM(model); //throws an error
}
}
private void InitializeContactVM(ContactVM model)
{
model.Customer = cm.GetViewFindCustomerDetails((int)model.CustomerId);
model.ContactClassificationList = AddBlankToList(SelectLists.ContactClassifications(false));
model.ContactSourceList = AddBlankToList(SelectLists.ContactSources(false));
}
}
And my unit test looks like this:
public void Edit_Contact_Update_Existing_Contact()
{
var dataManager = new Mock<IReferenceDataManager>();
//dataManager.Setup(a=>a.GetContactClassifications()).Returns()
var contact = InitializeContact();
var contactvm = new ContactVM(contact);
var fileMock = new Mock<HttpPostedFileBase>();
var files = new[] {fileMock.Object};
var mocManager = InitializeMocManagerContact();
mocManager.Setup(a => a.GetContactById(It.IsAny<int>())).Returns(contact);
mocManager.Setup(a => a.UpdateContact(It.IsAny<ContactVM>(), It.IsAny<string>())).Returns(contact);
var controller = new CustomerController(mocManager.Object);
var controllerContext = InitializeContext();
controller.ControllerContext = controllerContext.Object;
// mocManager.CallBase = true;
var result = controller.EditContact(contactvm, files, PageAction.Default) as ViewResult;
var model = result.ViewData.Model as ContactVM;
Assert.IsTrue(model.ContactId == contact.CONTACT_ID);
}
The problem is in the private method where it calls SelectLists.ContactClassifications(false), it then tries to hit the database.
The SelectList class is defined like
public static class SelectLists
{
private static readonly ReferenceDataManager _dataManager = new ReferenceDataManager();
public static SelectList ContactClassifications(bool includeDeleted)
{
var data = _dataManager.GetContactClassifications();
}
}
and it is the line where it calls GetContactClassifications in the SelectList that it feels like I should be able to mock (if the method that calls it can't be mocked because it is static). This one does implement an interface.
Even if there is some way that the private method in the Controller (InitialiseContactVM) could be mocked it would suit me.
Is there any way to achieve any of these things?

Ideally, your DAL should not be made out of static methods, but normal objects that provide services injected though an interface into controllers or whatever needs it.
But if you can't/don't want to change it, you the "standard" way to let you mock it would be to decouple the static method call from your controller. It can be done by wrapping it in a class that contains the static call and implements an interface, that is injected in the controller, and therefore mocked out in the tests. It's somewhat similar to testing a MessageBox call or the current system date/time.
First create an interface that will contain your static method calls:
public interface ISelectListsWrapper
{
SelectList ContactClassifications(bool includeDeleted);
}
Then a class will implement it by calling the actual static method:
public class SelectListsWrapper : ISelectListsWrapper
{
public SelectList ContactClassifications(bool includeDeleted)
{
return SelectLists.ContactClassifications(includeDeleted);
}
}
In the controller, you take an instance of this class in the constructor, save it to a local variable, and use that to call the static method though the wrapper:
private readonly ISelectListsWrapper selectLists;
public CustomerController(ICustomerManager customerMan, ISelectListsWrapper selectLists)
{
cm = customerMan;
this.selectLists = selectLists;
}
private void InitializeContactVM(ContactVM model)
{
model.Customer = cm.GetViewFindCustomerDetails((int)model.CustomerId);
model.ContactClassificationList = AddBlankToList(this.selectLists.ContactClassifications(false));
model.ContactSourceList = AddBlankToList(this.selectLists.ContactSources(false));
}
Finally, in the test, you just pass a mock of the wrapper and setup it to return whatever makes sense to that test.

The SelectLists class should be refactored to allow you to inject an IReferenceDataManager rather than instantiating one itself.

How do I use ninject to inject a session object property?

I have a service object that does some work on a particular patient.
public class PatientDxService
{
public Patient Patient { get; set; }
public PatientDxService(Patient patient)
{
this.Patient = patient;
}
}
My service takes in a Patient object as shown above.
I have a SessionManager object that has a property to get the session Patient. I want to inject the patient.
Bind<PatientDxService>().ToConstructor(x => new PatientDxService(x.Inject<ISessionManager>().Patient));
Bind<ISessionManager>().To<SessionManager>().InSingletonScope();
The above does not work for me. I don't really want to inject ISessionManager because if I wanted to use the services outside of the web scope, it wouldn't make sense.

Inject the ISessionManager into your Service instead of the Patient. then in constructor (or better yet, where you actually use the Patient), request the Patient from the session.
public class PatientDxService
{
private readonly ISessionManager _session;
public PatientDxService(ISessionManager session)
{
this._session = session;
}
public void DoStuff()
{
var patient = _session.GetPatient();
...
}
}

Implementing just a little IOC for MVC 3

I'm working on a design that will allow me to mock out my database so I can test my views. I don't want to read a full book on IOC because I don't have the time right now. So, this is my home cooking.
Controller:
public ActionResult Milestone()
{
var result = SJMServiceFactory.GetService("Milestone");
return View(result);
}
Factory:
public static class SJMServiceFactory
{
public static DatabaseCollection_Result<T> GetService(string serviceName)
{
switch(serviceName)
{
case("Milestone"): return MileStoneService.GetMilestone();
case ("MilestoneMock"): return MileStoneService.GetMilestone(true);
default : return default(T);
}
}
}
MileStone
public class MileStoneService
{
public MileStoneService()
{
}
public static DatabaseCollection_Result<Milestone> GetMilestone(bool Mock)
{
if (Mock)
{
DatabaseCollection_Result<Milestone> mileStones = new DatabaseCollection_Result<Milestone>();
Milestone milestone1 = new Milestone();
milestone1.Name = "New";
Milestone milestone2 = new Milestone();
milestone2.Name = "Assessment";
mileStones.Results.Add(milestone1);
mileStones.Results.Add(milestone2);
return mileStones;
}
else
return null;
}
}
I figure I need to return an interface from my factory instead of that Generic type I tried and failed at doing. I don't know how to create an interface that works for all my models, is that the wrong direction?

Without reading a whole book (does one exist? IoC is a pretty small topic in the scheme of things):
Controller:
private readonly IMilestoneService milestoneSerivce;
public MilestoneController(IMilestoneService milestoneService)
{
this.milestoneService = milestoneService;
}
public ActionResult Milestone()
{
var result = milestoneService.GetMilestones();
return View(result);
}
IMilestoneService.cs
public interface IMilestoneService
{
DatabaseCollection_Result<Milestone> GetMilestones();
}
MilestoneService.cs
public class MilestoneService : IMilestoneService
{
public DatabaseCollection_Result<Milestone> GetMilestones()
{
return null;
}
}
MockMilestoneService.cs:
public class MockMilestoneService : IMilestoneService
{
public DatabaseCollection_Result<Milestone> GetMilestones()
{
DatabaseCollection_Result<Milestone> mileStones = new DatabaseCollection_Result<Milestone>();
Milestone milestone1 = new Milestone();
milestone1.Name = "New";
Milestone milestone2 = new Milestone();
milestone2.Name = "Assessment";
mileStones.Results.Add(milestone1);
mileStones.Results.Add(milestone2);
return mileStones;
}
}
Global.asax:
ObjectFactory.Configure(x => {
x.For<IMilestoneService>().Use<MilestoneService>();
// uncomment for test
//x.For<IMilestoneService>().Use<MockMilestoneService>();
});
This uses StructureMap, but I imagine the Ninject way to wiring up the dependencies is similar. Having never used Ninject I don't know for sure, but it looks like it might be something like:
Bind<IMilestoneService>().To<MilestoneService>();
In general though I wouldn't go about creating a whole new class to test your Views, I would use a mocking framework such as Moq to create mock objects and pass them to the View and then use Assertions about the ViewResult to determine if it worked correctly.
If you're doing interactive testing though and want to be detached from the database, this might be an ok approach.

Don't fear the learning curve. IoC is a reasonably simple concept.
Ninject was the first container I picked up, and it went smoothly. The only point I really struggled with for any amount of time was how to organize all the bindings, but even that was only an issue in large applications.
YMMV, but I'd say just diving in with Ninject or similar is better investment of time than DIY.
IoC with Ninject only takes code in a few places.
1: Bind you interfaces to implementations:
public class ServiceModule : NinjectModule
{
public override void Load() {
Bind<Common.Billing.AuthorizeNet.IBillingGatewayParametersFactory>().To<AuthorizeNetParameterFactory>();
Bind<Common.Billing.IBillingGateway>().To<Common.Billing.AuthorizeNet.BillingGateway>();
}
}
2: Use constructor arguments to pass dependencies into a class:
public class BillPayingService
{
private readonly IBillingGateway _billingGateway;
public BillPayingService(
IBillingGateway billingGateway
)
{
_billingGateway = billingGateway;
}
public void PayBills()
{
// ....
}
}
3: Initialize your container on application startup:
public static class Ioc
{
public static void Initialize()
{
var modules = new INinjectModule[] {
new ServicesModule(),
new DataModule()
new VideoProcessing.NinjectModule()
};
IKernel kernel = new Ninject.StandardKernel(modules);
}
}