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Matching interface implementation with subtype to implemented type

tl;dr: I want the list List<ComponentDefinition> in the CellObjectDefinition class to be able to be checked with a type check ICellObjectDefinition<IComponentDefinition>.
ComponentDefinition is unknown at runtime and must therefore be testable with IComponentDefinition.
I have the following class:
public interface IComponentDefinition {}
public class ComponentDefinition : IComponentDefinition {}
public interface ICellObjectDefinition<TCDef>
{
public List<TCDef> Components { get; set; }
}
public class CellObjectDefinition : ICellObjectDefinition<ComponentDefinition>
{
public List<ComponentDefinition> Components { get; set; } = new();
}
I would have liked to keep the type ComponentDefinition in this list as the elements are added dynamically with reflection elsewhere. I want to validate the elements with their associated interfaces.
I don't quite understand why the list doesn't match the interface when I check the list filled with ComponentDefinition elements with ICellObjectDefinition<IComponentDefinition>.
Even an interface without a generic type does not work:
public interface ICellObjectDefinition<IComponentDefinition>
{
public List<IComponentDefinition> Components { get; set; }
}
Here is an executable sample code: https://dotnetfiddle.net/tpiNgJ

Depended on the actual use case you can make your interface covariant:
public interface ICellObjectDefinition<out TCDef> : IObjectDefinition
{
public IReadOnlyCollection<TCDef> Components { get; }
}
Which will require some implementation changes (using explicit interface implementation):
public partial class CellObjectDefinition : ObjectDefinition, ICellObjectDefinition<ComponentDefinition>
{
IReadOnlyCollection<ComponentDefinition> ICellObjectDefinition<ComponentDefinition>.Components => Components; // explicitly implement the interface
public List<ComponentDefinition> Components { get; set; } = new();
}
Full running code - at dotnetfiddle.

Generic Class Lists used with Strategy Pattern

I want to use generic classes with strategy pattern along with dependency injection in Asp.net
Definition of interface and concrete class
public interface IPaymentMethod<T>
{
string Name { get; set }
}
public interface PaymentMethod<T> : IPaymentMethod<T> where T: class
{
public string Name { get; set; }
}
Startup.cs
services.AddScoped(typeof(IPaymentMethod<>), typeof(PaymentMethod<>));
In the application
public class PaymentResolver
{
public PaymentResolver(List<IPaymentMethod<????>> paymentMethods)
{ ... }
public IPaymentMethod Resolve(string name)
{
return _paymentMethods.FirstOrDefault(item => item.Name == name);
}
}
How can I get the collection of IPaymentMethod instances from the dependency injection? PaymentResolver.Resolve method doesn't seem to be correct.

What you are looking for is kind of conflict to your self. So basically, you want to get a service when you know the service name. Then, my question is if you know service name
_paymentResolver.GetPaymentMethod("CreditCard/DebitCard")
you must know service type as well
class Invoice
{
public Invoice(IPaymentMethod<CreditCard> cc, IPaymentMethod<DeditCard> dc) {}
}
So what stops you from using a type rather than a name? Not to mention that it offers you strongly type so you don't have a risk of mistype the name.
Hope this helps clear your mind.

Couple related types together to control use in code using generics

I am trying to limit the use of types by chaining the aggregate IAggregate, the aggregate event IDomainEvent, and Identity together with generics, I have snipped the below code to give context of the issue of what I have got so far.
I have the following interfaces:
public abstract class Identity<T>
{
protected abstract string GetIdentity();
}
public interface IAggregate<T>
{
Identity<T> Identity { get; }
}
public interface IDomainEvent<TIdentity,TIdentity>
where T : Identity<TIdentity>
{
TIdentity Id { get; }
}
I implement with the below:
public class TestUserId : Identity<TestUser>
{
public TestUserId(string name) { Name = name; }
readonly public string Name;
protected override string GetIdentity() => Name.ToLowerInvariant();
}
public class TestUser : IAggregate<TestUser>
{
public TestUser(TestUserId id)
{
Id = id;
var ev = new TestUserCreated()
}
public TestUserId Id { get; }
public Identity<TestUser> Identity => Id;
}
public class TestUserCreated : IDomainEvent<TestUserId, TestUser>
{
public TestUserCreated() { }
public TestUserId Id => throw new NotImplementedException();
}
Then in the command handler, for this event to be used (and for me to be able to obtain the TestUserId which should be member of the domainEvent object).
public interface IDomainEventHandler<TEvent>
{
void Handle(TEvent domainEvent, bool isReplay);
}
That gives me the code:
public class TesterHandler : IDomainEventHandler<TestUser, TestUserCreated>
{
public void Handle(TestUserCreated domainEvent, bool isReplay)
{
// can access the ID (of type TestUserId)
var testUserId = domainEvent.Id;
}
}
So the above TesterHandler is fine exactly how i would want - however the compiler is failing on class TestUserCreated : IDomainEvent<TestUserId, TestUser> with The type TestUserId' cannot be used as type parameter 'TIdentity' in the generic type or method 'IDomainEvent<TIdentity, Type>'. There is no implicit reference conversion from 'TestUserId' to 'Identity<TestUser>'.
What I want is to couple (without OO inheritance) the event to the aggregate, so that it is tied to a specific aggregate type (i.e. specific events are tied to a specific entity, and the entity ID is part of the event type as a field), I want to try and make it impossible to code event handlers for unrelated aggregates.
I am trying to implement but the compiler complains of boxing and implicit casting errors (depending on what i try/guess), in short I am unsure how to code the above.

Given I was unable to create running code as per comments requested (hence the reason for the post) and general complexity, I decided using generics in this way was a bad idea with rationale below.
I currently have code which calls the handler as follows (and this is working fine) passing in the sourceIdentity external to the domainEvent object:
public interface IDomainEventHandler<TIdentity, TEvent>
where TIdentity : IIdentity
where TEvent : IDomainEvent
{
void Handle(TIdentity sourceIdentity, TEvent domainEvent, bool isReplay);
}
I am passing in the aggregate ID external to the IDomainEvent object (and this is desired to keep the events, from an event sourcing perspective, as simple as possible as simple POCO objects without inheritance or involving any framework).
The reason for the question was I just wanted to explore all options with generics (so the domainEvent object could have an interface that would give an ID field) but it started to get complicated quickly, specifically additional template parameters would be required since we are inferring relationships via templates, rather than OO relationships.
Without OO, the relationship would need to be defined somewhere by adding additional types to templates to tie them together interface IDomainEvent<TIdentity,TAggregate,TEvent> and interface IDomainEventHandler<TIdentity, TAggregate, TEvent>, in this case OO inheritance would be preferred and result in way less code.
All this was done to give an interface to obtain the ID, however as if an ID is really needed it can be incorporated in the event as a normal field (without the need for complex OO relationships or templates).
public interface IDomainEvent
{
DateTime OccurredOn { get; set; }
Guid MessageId { get; set; }
}
public class TestUserCreated : IDomainEvent
{
// id can be accessed by whatever needs it by being
// defined explicity within the domain event POCO
// without needing any base class or framework.
public readonly TestUserId Id;
public readonly string Name;
public TestUserCreated(TestUserId id, string name)
{
Id = id;
Name = name;
}
}

Specify interface member not by name but type

I have a lot of similar classes generated by svcutil from some external WSDL file. Any class has a Header property and string property which named class name + "1".
For instance, I have classes: SimpleRequest that has Header property and SimpleRequest1 property.
Another one is ComplexRequest that has Header property and ComplexRequest1 property.
So, I want to create a common interface for such classes. So, basically I can define something like that:
interface ISomeRequestClass {
string Header;
// here is some definition for `class name + "1"` properties...
}
Is it possible to define such member in interface?
Here is post edit goes...
Here is sample of generated class:
[System.Diagnostics.DebuggerStepThroughAttribute()]
[System.CodeDom.Compiler.GeneratedCodeAttribute("System.ServiceModel", "3.0.0.0")]
[System.ServiceModel.MessageContractAttribute(IsWrapped=false)]
public partial class SimpleRequest
{
public string Header;
[System.ServiceModel.MessageBodyMemberAttribute(Name="SimpleRequest", Namespace="data", Order=0)]
public SimpleRequestMsg SimpleRequest1;
public SimpleRequest()
{
}
public SimpleRequest(string Header, SimpleRequestMsg SimpleRequest1)
{
this.Header = Header;
this.SimpleRequest1 = SimpleRequest1;
}
}
POST EDIT 2
I changed definition of this annoying +1 property to represent real actual picture. It's all has different class types. So how can I pull it out to common interface?
POST EDIT 3
Here is coupled question that could bring more clarify.

EDIT (after seeing your code sample): Technically speaking, your code does not have a Header property, it has a Header field. This is an important difference, since you cannot specify fields in an interface. However, using the method described below, you can add properties to your classes that return the field values.
Is it possible to define such member in interface?
No, interface names cannot be dynamic. Anyway, such an interface would not be very useful. If you had an instance of class ISomeRequestClass, what name would you use to access that property?
You can, however, use explicit interface implementation:
interface ISomeRequestClass {
string Header { get; set; }
string ClassName1 { get; set; }
}
class SomeClass : ISomeRequestClass {
string Header { ... }
string SomeClass1 { ... }
// new: explicit interface implementation
string ISomeRequestClass.ClassName1 {
get { return SomeClass1; }
set { SomeClass1 = value; }
}
}

You could define your interface more generally:
interface ISomeRequestClass {
string HeaderProp {get; set;}
string Prop {get; set;}
}
And your concrete classes could be extended (in an extra code file) by mapping interface members to class fields like so:
public partial class SimpleRequest : ISomeRequestClass
{
public string HeaderProp
{
get
{
return Header;
}
set
{
Header = value;
}
}
public string Prop
{
get
{
return SimpleRequest1;
}
set
{
SimpleRequest1= value;
}
}
}

Putting aside for a moment the naming of your classes and properties.
If you're looking to create an interface with a property relevant to your specific +1 type, you have a couple of options.
Use a base class for your +1's
If both of your +1 classes inherit from the same base class you can use this in your interface definition:
public interface IFoo
{
[...]
PlusOneBaseType MyPlusOneObject{get;set;}
}
Create a generic property on your interface
This method allows you to specify the type for the +1 property as a generic parameter:
public interface IFoo<TPlusOneType>
{
[...]
TPlusOneType MyPlusOneObject{get;set;}
}
Which you might use like:
public class SimpleRequest : IFoo<SimpleRequest1>
{
[...]
}
Update
Given that your classes are partial classes, you could always create a second (non machine generated) version of the partial class that impliments your interface.

You mentioned svcutil so I assume you are using these classes as WCF DataContracts?
If that is the case then you could make use the name property of DataMemberAttribute.
interface IRequest
{
string Header { get; set; }
string Request1 { get; set; }
}
[DataContract]
class SimpleRequest : IRequest
{
[DataMember]
public string Header { get; set; }
[DataMember(Name="SimpleRequest1"]
public string Request1 { get; set; }
}
[DataContract]
class ComplexRequest : IRequest
{
[DataMember]
public string Header { get; set; }
[DataMember(Name="ComplexRequest1"]
public string Request1 { get; set; }
}
If you are concerned giving yourself more work when you regenerate the code at some point in the future, then I recommend you write a PowerShell script to do this transformation automatically. After all svcutil is just a script written by some guy at Microsoft. It is not magic or "correct" or "standard". Your script can make a call to scvutil and then make a few quick changes to the resulting file.
EDIT (After seeing your edit)
You are already using MessageBodyMemberAttribute's Name property so just change this:
public string SimpleRequest1;
To
public string Request1;

Do you actually need these classes to have a common interface? I'd be tempted to instead create a wrapper interface (or just a concrete class) which could then use reflection to access the fields in question:
// TODO: Make this class implement an appropriate new interface if you want
// to, for mocking purposes.
public sealed class RequestWrapper<TRequest, TMessage>
{
private static readonly FieldInfo headerField;
private static readonly FieldInfo messageField;
static RequestWrapper()
{
// TODO: Validation
headerField = typeof(TRequest).GetField("Header");
messageField = typeof(TRequest).GetField(typeof(TRequest).Name + "1");
}
private readonly TRequest;
public RequestWrapper(TRequest request)
{
this.request = request;
}
public string Header
{
get { return (string) headerField.GetValue(request); }
set { headerField.SetValue(request, value); }
}
public TMessage Message
{
get { return (TMessage) messageField.GetValue(request); }
get { messageField.SetValue(request, value); }
}
}
You could use expression trees to build delegates for this if the reflection proves too slow, but I'd stick to a simple solution to start with.
The advantage of this is that you only need to write this code once - but it does mean creating a wrapper around the real request objects, which the partial class answers don't.

Creating read-only versions of classes in a complex object structure

In my current project I need to be able to have both editable and read-only versions of classes. So that when the classes are displayed in a List or PropertGrid the user is not able to edit objects they should not be allowed to.
To do this I'm following the design pattern shown in the diagram below. I start with a read-only interface (IWidget), and then create an edtiable class which implements this interface (Widget). Next I create a read-only class (ReadOnlyWidget) which simply wraps the mutable class and also implements the read only interface.
I'm following this pattern for a number of different unrelated types. But now I want to add a search function to my program, which can generate results that include any variety of types including both mutable and immutable versions. So now I want to add another set of interfaces (IItem, IMutableItem) that define properties which apply to all types. So IItem defines a set of generic immutable properties, and IMutableItem defines the same properties but editable. In the end a search will return a collection of IItems, which can then later be cast to more specific types if needed.
Yet, I'm not sure if I'm setting up the relationships to IMutable and IItem correctly. Right now I have each of the interfaces (IWidget, IDooHickey) inheriting from IItem, and then the mutable classes (Widget, DooHickey) in addition also implement IMutableItem.
Alternatively, I was also thinking I could then set IMutableItem to inherit from IItem, which would hide its read-only properties with new properties that have both get and set accessors. Then the mutable classes would implement IMutableItem, and the read-only classes would implement IItem.
I'd appreciate any suggestions or criticisms regarding any of this.
Class Diagram
Code
public interface IItem
{
string ItemName { get; }
}
public interface IMutableItem
{
string ItemName { get; set; }
}
public interface IWidget:IItem
{
void Wiggle();
}
public abstract class Widget : IWidget, IMutableItem
{
public string ItemName
{
get;
set;
}
public void Wiggle()
{
//wiggle a little
}
}
public class ReadOnlyWidget : IWidget
{
private Widget _widget;
public ReadOnlyWidget(Widget widget)
{
this._widget = widget;
}
public void Wiggle()
{
_widget.Wiggle();
}
public string ItemName
{
get {return _widget.ItemName; }
}
}
public interface IDoohickey:IItem
{
void DoSomthing();
}
public abstract class Doohickey : IDoohickey, IMutableItem
{
public void DoSomthing()
{
//work it, work it
}
public string ItemName
{
get;
set;
}
}
public class ReadOnlyDoohickey : IDoohickey
{
private Doohickey _doohicky;
public ReadOnlyDoohickey(Doohickey doohicky)
{
this._doohicky = doohicky;
}
public string ItemName
{
get { return _doohicky.ItemName; }
}
public void DoSomthing()
{
this._doohicky.DoSomthing();
}
}

Is it OK to create another object when you need a readonly copy? If so then you can use the technique in the included code. If not, I think a wrapper is probably your best bet when it comes to this.
internal class Test
{
private int _id;
public virtual int ID
{
get
{
return _id;
}
set
{
if (ReadOnly)
{
throw new InvalidOperationException("Cannot set properties on a readonly instance.");
}
}
}
private string _name;
public virtual string Name
{
get
{
return _name;
}
set
{
if (ReadOnly)
{
throw new InvalidOperationException("Cannot set properties on a readonly instance.");
}
}
}
public bool ReadOnly { get; private set; }
public Test(int id = -1, string name = null)
: this(id, name, false)
{ }
private Test(int id, string name, bool readOnly)
{
ID = id;
Name = name;
ReadOnly = readOnly;
}
public Test AsReadOnly()
{
return new Test(ID, Name, true);
}
}

I would suggest that for each main class or interface, there be three defined classes: a "readable" class, a "changeable" class, and an "immutable" class. Only the "changeable" or "immutable" classes should exist as concrete types; they should both derive from an abstract "readable" class. Code which wants to store an object secure in the knowledge that it never changes should store the "immutable" class; code that wants to edit an object should use the "changeable" class. Code which isn't going to write to something but doesn't care if it holds the same value forever can accept objects of the "readable" base type.
The readable version should include public abstract methods AsChangeable(), AsImmutable(), public virtual method AsNewChangeable(), and protected virtual method AsNewImmutable(). The "changeable" classes should define AsChangeable() to return this, and AsImmutable to return AsNewImmutable(). The "immutable" classes should define AsChangeable() to return AsNewChangeable() and AsImmutable() to return this.
The biggest difficulty with all this is that inheritance doesn't work terribly well if one tries to use class types rather than interfaces. For example, if one would like to have an EnhancedCustomer class which inherits from BasicCustomer, then ImmutableEnhancedCustomer should inherit from both ImmutableBasicCustomer and ReadableEnhancedCustomer, but .net doesn't allow such dual inheritance. One could use an interface IImmutableEnhancedCustomer rather than a class, but some people would consider an 'immutable interace' to be a bit of a smell since there's no way a module that defines an interface in such a way that outsiders can use it without also allowing outsiders to define their own implementations.

Abandon hope all ye who enter here!!!
I suspect that in the long run your code is going to be very confusing. Your class diagram suggests that all properties are editable (or not) in a given object. Or are your (I'm)mutable interfaces introducing new properties that are all immutable or not, separate from the "core"/inheriting class?
Either way I think you're going to end up with playing games with property name variations and/or hiding inherited properties
Marker Interfaces Perhaps?
Consider making all properties in your classes mutable. Then implement IMutable (I don't like the name IItem) and IImutable as a marker interfaces. That is, there is literally nothing defined in the interface body. But it allows client code to handle the objects as a IImutable reference, for example.
This implies that either (a) your client code plays nice and respects it's mutability, or (b) all your objects are wrapped by a "controller" class that enforces the given object's mutability.

Could be too late :-), but the cause "The keyword 'new' is required on property because it hides property ..." is a bug in Resharper, no problem with the compiler. See the example below:
public interface IEntityReadOnly
{
int Prop { get; }
}
public interface IEntity : IEntityReadOnly
{
int Prop { set; }
}
public class Entity : IEntity
{
public int Prop { get; set; }
}
[TestClass]
public class UnitTest1
{
[TestMethod]
public void TestMethod1()
{
var entity = new Entity();
(entity as IEntity).Prop = 2;
Assert.AreEqual(2, (entity as IEntityReadOnly).Prop);
}
}
Same for the case without interfaces. The only limitation, you can't use auto-properties
public class User
{
public User(string userName)
{
this.userName = userName;
}
protected string userName;
public string UserName { get { return userName; } }
}
public class UserUpdatable : User
{
public UserUpdatable()
: base(null)
{
}
public string UserName { set { userName = value; } }
}
[TestClass]
public class UnitTest1
{
[TestMethod]
public void TestMethod1()
{
var user = new UserUpdatable {UserName = "George"};
Assert.AreEqual("George", (user as User).UserName);
}
}