I'm creating an application with multiple plugins using MEF2 (Microsoft.Composition). These plugins should import some common object and they should all share the same instance of this object... so a typical Singleton.
However, when I [Import] this common object into my plugins they all get their own copy instead of a shared one.
In .NET Framework MEF1, all object were created as singletons by default. This does not seem to be the case for .NET Core MEF2.
How can I make sure that all my plugins get the same singleton instance of my common object?
Sample code
Startup
static void Main(string[] args) {
ContainerConfiguration containerConfig = new ContainerConfiguration()
.WithAssembly(Assembly.GetExecutingAssembly())
.WithAssembly(typeof(ICommonObject).Assembly);
using (CompositionHost container = containerConfig.CreateContainer()) {
_mainApp = container.GetExport<MainApp>();
_mainApp.Start();
}
}
MainApp
[Export(typeof(MainApp))]
public class MainApp {
[Import] public ICommonObject CommonObject { get; set; }
[ImportMany] public IEnumerable<IPlugin> Plugins { get; set; }
public void Start() {
CommonObject.SomeValue = "foo";
Console.WriteLine("SomeValue (from MainApp): " + CommonObject.SomeValue);
foreach (IPlugin plugin in Plugins) {
plugin.Start();
}
}
}
Plugin
[Export(typeof(IPlugin))]
public class SomePlugin : IPlugin {
[Import] public ICommonObject CommonObject { get; set; }
public void Start() {
Console.WriteLine("SomeValue (from plugin): " + CommonObject.SomeValue);
}
}
Output
SomeValue (from MainApp): foo
SomeValue (from plugin):
After much trial and error I seem to have finally found a solution myself.
The trick seems to be to use ConventionBuilder. This has an extension method called .Shared() which makes all objects derived from a specific type into a Singleton.
For my code examples, just add the following to the top of the Startup code:
ConventionBuilder conventions = new ConventionBuilder();
conventions.ForTypesDerivedFrom<ICommonObject>()
.Export<ICommonObject>()
.Shared();
ContainerConfiguration containerConfig = new ContainerConfiguration()
.WithAssembly(Assembly.GetExecutingAssembly(), conventions);
For some reason, the object implementing ICommonObject doesn't even need an [Export] attribute. In any case, the output from the example is now:
SomeValue (from MainApp): foo
SomeValue (from plugin): foo
Related
I'm working on a new project that uses CosmosDB and Entity Framework Core (via the Microsoft.EntityFrameworkCore.Cosmos NuGet package, version 5.0.7; the project itself is .NET Core 5). I'm new to both, and running into an issue I can't sort out.
In short, I need to save a complex object to the database. It's a big model that will have multiple collections of classes underneath it, each with their own properties and some with collections underneath them as well. I'm trying to configure EF with OwnsOne and OwnsMany to store these child objects underneath the top-level one. The code compiles, and will save to the database so long as all the owned objects are left empty. But whenever I put anything into an owned object, either with OwnsOne or OwnsMany, I get a pair of NullReferenceExceptions.
I've tried to strip my code down to the very basics. Here's how it currently looks.
Owner and owned classes:
public class Questionnaire
{
// Constructors
private Questionnaire() { }
public Questionnaire(Guid id)
{
Test = "Test property.";
TV = new TestQ();
Id = id;
}
public Guid Id { get; set; }
public string Test { get; set; }
public TestQ TV { get; set; }
// Public Methods
public void AddForm(Form f)
{
// not currently using this method
//Forms.Add(f);
}
}
public class TestQ
{
public TestQ()
{
TestValue = "test ownsone value";
}
public string TestValue { get; set; }
}
DbContext:
public class QuestionnaireDbContext : DbContext
{
public DbSet<Questionnaire> Questionnaires { get; set; }
public QuestionnaireDbContext(DbContextOptions<QuestionnaireDbContext> options) : base(options) { }
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
modelBuilder.HasDefaultContainer(nameof(Questionnaires));
modelBuilder.Entity<Questionnaire>().HasKey(q => q.Id);
modelBuilder.Entity<Questionnaire>().OwnsOne(q => q.TV);
}
}
And the code from the service that calls the dbContext (note that this is based on a generic service that I didn't set up originally). The actual exceptions are thrown here.
public virtual TEntity Add(TEntity entity)
{
_context.Entry(entity).State = EntityState.Added;
_context.SaveChanges();
return entity;
}
Ultimately I need this to work with OwnsMany and a collection, but I figured it might be simpler to get it working with OwnsOne first. The key thing to note here is that if I comment out the line
TV = new TestQ();
in the Questionnaire class, the model persists correctly into CosmosDB. It's only when I actually instantiate an owned entity that I get the NullReferenceExceptions.
Any advice would be much appreciated! Thank you!
Well, I'm not sure why this is the case, but the issue turned out to be with how we were adding the document. Using this generic code:
public virtual async Task<TEntity> Add(TEntity entity)
{
_context.Entry(entity).State = EntityState.Added;
await _context.SaveChanges();
return entity;
}
was the issue. It works just fine if I use the actual QuestionnaireDbContext class like so:
context.Add(questionnaire);
await context.SaveChangesAsync();
I am having problems understanding how to use RegisterFactory. The code below works fine with the older InjectionFactory but I am having problems when I try to do the same thing with RegisterFactory.
In the sample code there is an uncommented section that uses RegisterFactory and a commented section that uses InjectionFactory. The InjectionFactory code works fine but the RegisterFactory throws an ResolutionFailedException.
Unity.ResolutionFailedException: 'The current type, ConsoleApp1.IFoo, is an interface and cannot be constructed. Are you missing a type mapping?
What am I doing incorrectly?
class Program
{
static void Main(string[] args)
{
var container = new UnityContainer();
container.EnableDebugDiagnostic();
container.RegisterType<IFoo, Foo1>("Foo1");
container.RegisterType<IFoo, Foo2>("Foo2");
container.RegisterType<MainViewModel>();
// This does not work
container.RegisterFactory<Func<string, IFoo>>((c, type, name) => c.Resolve<IFoo>(name));
// This works
//container.RegisterType<Func<string, IFoo>>(new InjectionFactory(
// ctx => new Func<string, IFoo>(name => container.Resolve<IFoo>(name))));
var vm = container.Resolve<MainViewModel>();
}
}
public class MainViewModel
{
public MainViewModel(Func<string, IFoo> fooFactory)
{
var foo1 = fooFactory.Invoke("Foo1");
var foo2 = fooFactory.Invoke("Foo2");
}
}
public interface IFoo
{
string Name { get; }
}
public class Foo1 : IFoo
{
public string Name { get; set; }
public Foo1()
{
Name = "Foo1";
}
}
public class Foo2 : IFoo
{
public string Name { get; set; }
public Foo2()
{
Name = "Foo2";
}
}
If you're registering with RegisterFactory, you tell Unity how to construct the instance. But Unity already knows how to construct Foo1 and Foo2, because you registered those already.
What you want is a factory for you to use, that's what RegisterType does, so this works.
Normally, such a factory would implement some IFooFactory, thus making the context more obvious. But as long as Func<string, IFoo> is registered only used once, it works fine, too, of course.
I want to change my session proviced to statically typed - I just hate typing strings because of many many errors I do.
What technology am I using? ASP.NET MVC via EXT.NET MVC
I was trying to do that using web.config but the problem is that after add session state to it visual is not going to compile my code because of that session should be using strings as keys.
I want to use session by enums such as :
public enum SessionEnum{Model}
public class Bar{
void foo(){
Session[SessionEnum.Model] = "blah";
}
}
I am aware that I can create wrapper converting enums to strings but it's not very satisfying solution for me.
public class StorageWrapper{
public object this[SessionEnum enum]{ get{return Session[enum.toString()]}; //+set
}
What I did was create static object for base class for all of my controllers and then I was able to use it across them but after closing and opening the page again I wasn't able to get values from it. I guess I should serialize them somehow but I have no idea how.
Is there any way to do that?
EDIT
My session now looks like this :
[Serializable]
public abstract class DataWrapper<T> : HttpSessionStateBase
{
Dictionary<T, object> Dictionary { get; set; } = new Dictionary<T, object>();
public object this[T a]
{
get
{
try
{
return Dictionary[a];
}
catch
{
return null;
}
}
set { Dictionary[a] = value; }
}
}
[Serializable]
public class SessionWrapper : DataWrapper<SessionNames>
{}
public enum SessionNames { Model, Login, LastOpenedFile }
It's very simple.
Create a UserSession object which does everything you want (holds your values as enum etc), instantiate it, then put it in the session.
var US = new UserSession();
US.stuff = somestuff;
Session["UserSess"] = US
Then you can just always use Session["UserSess"].stuff;
Mmmm, wouldn't you use static const string instead of an enum?
using System.Web;
public static class SessionEnum
{
public static const string Model = "_Session_Model";
public static const string Login = "_Session_Login";
public static const string LastOpenedFile = "_Session_LastOpenedFile ";
}
class test
{
void test()
{
Session[SessionEnum.Model] = "blah";
}
}
I am going though the Apress ASP.NET MVC 3 book and trying to ensure I create Unit Tests for everything possible but after spending a good part of a day trying to work out why edit's wouldn't save (see this SO question) I wanted to create a unit test for this.
I have worked out that I need to create a unit test for the following class:
public class EFProductRepository : IProductRepository {
private EFDbContext context = new EFDbContext();
public IQueryable<Product> Products {
get { return context.Products; }
}
public void SaveProduct(Product product) {
if (product.ProductID == 0) {
context.Products.Add(product);
}
context.SaveChanges();
}
public void DeleteProduct(Product product) {
context.Products.Remove(product);
context.SaveChanges();
}
}
public class EFDbContext : DbContext {
public DbSet<Product> Products { get; set; }
}
I am using Ninject.MVC3 and Moq and have created several unit tests before (while working though the previously mentioned book) so am slowly getting my head around it. I have already (hopefully correctly) created a constructor method to enable me to pass in _context:
public class EFProductRepository : IProductRepository {
private EFDbContext _context;
// constructor
public EFProductRepository(EFDbContext context) {
_context = context;
}
public IQueryable<Product> Products {
get { return _context.Products; }
}
public void SaveProduct(Product product) {
if (product.ProductID == 0) {
_context.Products.Add(product);
} else {
_context.Entry(product).State = EntityState.Modified;
}
_context.SaveChanges();
}
public void DeleteProduct(Product product) {
_context.Products.Remove(product);
_context.SaveChanges();
}
}
BUT this is where I start to have trouble... I believe I need to create an Interface for EFDbContext (see below) so I can replace it with a mock repo for the tests BUT it is built on the class DbContext:
public class EFDbContext : DbContext {
public DbSet<Product> Products { get; set; }
}
from System.Data.Entity and I can't for the life of me work out how to create an interface for it... If I create the following interface I get errors due to lack of the method .SaveChanges() which is from the DbContext class and I can't build the interface using "DbContext" like the `EFDbContext is as it's a class not an interface...
using System;
using System.Data.Entity;
using SportsStore.Domain.Entities;
namespace SportsStore.Domain.Concrete {
interface IEFDbContext {
DbSet<Product> Products { get; set; }
}
}
The original Source can be got from the "Source Code/Downloads" on this page encase I have missed something in the above code fragments (or just ask and I will add it).
I have hit the limit of what I understand and no mater what I search for or read I can't seem to work out how I get past this. Please help!
The problem here is that you have not abstracted enough. The point of abstractions/interfaces is to define a contract that exposes behavior in a technology-agnostic way.
In other words, it is a good first step that you created an interface for the EFDbContext, but that interface is still tied to the concrete implementation - DbSet (DbSet).
The quick fix for this is to expose this property as IDbSet instead of DbSet. Ideally you expose something even more abstract like IQueryable (though this doesn't give you the Add() methods, etc.). The more abstract, the easier it is to mock.
Then, you're left with fulfilling the rest of the "contract" that you rely on - namely the SaveChanges() method.
Your updated code would look like this:
public class EFProductRepository : IProductRepository {
private IEFDbContext context;
public EFProductRepository(IEFDbContext context) {
this.context = context;
}
...
}
public interface IEFDbContext {
IDbSet<Product> Products { get; set; }
void SaveChanges();
}
BUT... the main question you have to ask is: what are you trying to test (conversely, what are you trying to mock out/avoid testing)? In other words: are you trying to validate how your application works when something is saved, or are you testing the actual saving.
If you're just testing how your application works and don't care about actually saving to the database, I'd consider mocking at a higher level - the IProductRepository. Then you're not hitting the database at all.
If you want to make sure that your objects actually get persisted to the database, then you should be hitting the DbContext and don't want to mock that part after all.
Personally, I consider both of those scenarios to be different - and equally important - and I write separate tests for each of them: one to test that my application does what it's supposed to do, and another to test that the database interaction works.
I guess your current code looks something like this (I put in the interface):
public class EFProductRepository : IProductRepository {
private IEFDbContext _context;
// constructor
public EFProductRepository(IEFDbContext context) {
_context = context;
}
public IQueryable<Product> Products {
get { return _context.Products; }
}
public void SaveProduct(Product product) {
if (product.ProductID == 0) {
_context.Products.Add(product);
} else {
_context.Entry(product).State = EntityState.Modified;
}
**_context.SaveChanges();**
}
public void DeleteProduct(Product product) {
_context.Products.Remove(product);
**_context.SaveChanges();**
}
}
public class EFDbContext : DbContext, IEFDbContext {
public DbSet<Product> Products { get; set; }
}
public interface IEFDbContext {
DbSet<Product> Products { get; set; }
}
The problem is EFProductRepository now expects an object implementing the IEFDbContext interface, but this interface does not define the SaveChanges method used at the lines I put between the asteriskes so the compiler starts complaining.
Defining the SaveChanges method on the IEFDbContext interface solves your problem:
public interface IEFDbContext {
DbSet<Product> Products { get; set; }
void SaveChanges();
}
I want to mock my Repository object in such a way that it can still do actual DB retrieve operations. Only for Saving operations, I wanted to setup to return mock data since I don't want it to save into the DB.
How should I do it?
Thanks.
Maybe you should make your Save operation virtual and override it in a subclass which you use in your tests rather than using Moq?
First of all, your unit tests should never actually go out to the database (it is all right for integration tests, but that is a larger topic). What you want to do is pretty straightforward with Moq, though:
public class MyRepo
{
public virtual string Save(MyClass foo)
{
// perform save...
}
}
public class MyService
{
public MyRepo Repo { get; set; }
public string VerifyAndSave(MyClass foo)
{
// verify foo...
return new Repo.Save(foo);
}
}
public class MyClass()
{
public string SomeData { get; set; }
}
Notice the virtual modifiers on the methods--these are important for Moq to be able to stub them.
In your tests you could then do something like this:
[TestClass]
public class SomeTests
{
private Mock<MyRepo> MockRepo { get; set; }
private MyService Target { get; set; }
[TestInitialize]
public void Setup()
{
MockRepo = new Mock<MyRepo>();
Target = new MyService();
Target.Repo = MockRepo.Object;
}
[TestMethod]
public void MyTest()
{
const string expectedOutput = "SAVED";
MyClass exampleData = new MyClass();
MockRepo.Setup(x => x.Save(It.IsAny<MyClass>())).Returns(expectedOutput);
Target.VerifyAndSave(exampleData);
MockRepo.Verify(x => x.Save(It.IsAny<MyClass>()));
}
}
The chained calls of Setup and Returns in this case would guarantee that the calling method (i.e. VerifyAndSave) would see the value that you specified--"SAVED" in this case.
For more examples, take a look at the Moq quickstart docs.