Is there any practial reason to create interface for abstract class? I encountered such thing:
public interface IEntity<T>
{
T Id { get; set; }
}
public abstract class BaseEntity {
}
public abstract class Entity<T> : BaseEntity, IEntity<T>
{
public virtual T Id { get; set; }
}
and i really don't understand what is the difference between that and this code, because IEntity is not a thing i whould use more than once:
public abstract class BaseEntity {
}
public abstract class Entity<T> : BaseEntity
{
public virtual T Id { get; set; }
}
Thanks!
Since the BaseEntity class does actually add any properties of methods, yes, it is completely different from the interface. The interface defines a property Id of type T, and that interface (contract) can be used in other locations in your application.
The base class as it is now, is useless IMHO.
A base class which would implement the interface for you is something that would be usable, like this:
public interface IEntity<T> {
T Id { get; set; }
}
public abstract class BaseEntity<T>: IEntity<T> {
public virtual T Id { get; set; }
}
public abstract class Entity<T> : BaseEntity<T> {
// No need to implement the Id property, we already have it inherited
}
Here is the same thing with correct answer that i wanted to know: c# Abstract Class implementing an Interface
Thanks everyone for help.
Related
All of my models in all of my applications inherit from IEntity:
public interface IEntity
{
long Id { get; set; }
dynamic RelatedItems { get; set; }
}
To prevent NullReferenceException, I always write a constructor in each model:
public class Book : IEntity
{
public Book()
{
RelatedItems = new System.Dynamic.ExpandoObject();
}
// other properties of the book
}
I need the RelatedItems because my infrastructure does many things on it.
However, this boilerplate constructor is a true pain.
When C# introduced Default Implementation I thought maybe default constructors also exist now, thus I created a constructor in my IEntity interface.
But I got this error:
IEntity.cs(7,16): error CS0526: Interfaces cannot contain instance constructors
Is there a way that I can prevent this boilerplate code?
I once tried to change it to abstract base class but it messed with EF Core and its inheritance.
As #AlanK pointed out the easiest thing would be to create an abstract class providing a boilerplate implementation of your properties including any initializers like this:
public abstract class BaseEntitiy : IEntity
{
public virtual long Id { get; set; }
public virtual dynamic RelatedItems { get; set; } = new System.Dynamic.ExpandoObject();
}
you can then inherit your Book class from BaseEntity overriding properties as needed:
public class Book : BaseEntitiy
{
// example override if you need any special getters or setters for books
public override long Id
{
get => base.Id;
set
{
if (value > 0)
{
base.Id = value;
}
}
}
}
Take a look at this code.
It's better to use generic instead of dynamic, so I added a BookRelatedItem class which you can add any further properties to.
About the EntityBase class, it's an abstraction of your entities so you don't have to initialize your RelatedItems each time.
public interface IEntity<T> where T : class
{
long Id { get; set; }
IEnumerable<T> RelatedItems { get; set; }
}
public abstract class EntityBase<T> : IEntity<T> where T : class
{
public long Id { get; set; }
public IEnumerable<T> RelatedItems { get; set; }
public EntityBase()
{
RelatedItems = new List<T>();
}
}
public class Book : EntityBase<BookRelatedItem>
{
// other properties of the book
}
public class BookRelatedItem
{
//some props
}
I have this class, it's part of my specification pattern.
Following this link
public class SpecificationEvaluator<TEntity>
where TEntity : BaseEntity
and BaseEntity consists of just the id
ex.
public class BaseEntity
{
public int Id { get; set; }
}
and this works fine for all my entities that inherit 'BaseEntity'
ex.
Product : BaseEntity
Invoice : BaseEntity
Message : BaseEntity
now I want to use the specification pattern on my 'User' entity, so that I can provide specs/conditions and fetch lists of users.
But my problem is my projects 'User' entity doesn't inherit 'BaseEntity', it inherits 'IdentityUser'
ex.
public class User : IdentityUser<int>
{
}
I'm aware I can't have multiple classes as constraints, but I can have multiple interfaces.
I know I can set the constraint to just a 'class'
ex.
public class SpecificationEvaluator<TEntity>
where TEntity : class
{
}
but doesn't this sorta defeat the purpose of creating specific constraints?
QUESTION - Is there another solution I can implement to have both 'BaseEntity' and 'User'
as constraints?
It seems to me that you might have to do this:
public interface IIdentityUser<T>
{
T Id { get; set; }
}
public class SpecificationEvaluator<TEntity, T>
where TEntity : IIdentityUser<T>
{ }
public class BaseEntity : IIdentityUser<int>
{
public int Id { get; set; }
}
public class Product : BaseEntity { }
public class Invoice : BaseEntity { }
public class Message : BaseEntity { }
public class IdentityUser<T> : IIdentityUser<T>
{
public T Id { get; set; }
}
public class User : IdentityUser<int>
{
}
I have a rather simple problem, but I can't find a proper solution anywhere. I would like to specify an abstract object CustomValues as property in my abstract parent class. However, the class inheriting from it should be able to use a more specific type as an object for this property CustomValues. At first I thought I would solve the problem by an interface, but unfortunately that didn't work out either. How do you do something like that, that it works?
public abstract class MyAbstract {
public abstract object CustomValues { get; set; }
}
public class MyImplementation : MyAbstract {
public override MySpecificClass CustomValues { get; set; }
}
This will throw me three errors:
Missing implementation for getter
Missing implementation for setter
Type missmatch between type object and MySpecificClass
The solution suggested in the comments would look something like this. (I'm assuming CustomValues should be a collection of something.)
public class MyClass<T>
{
public ICollection<T> CustomValues { get; set; }
}
Or to ensure CustomValues itself cannot be reassigned, but can be accessed and added to:
public class MyClass<T>
{
public ICollection<T> CustomValues { get; } = new List<T>();
}
I think your original thought that use an interface (+ generic) was at the correct direction. In general you might want to add type constraints as well.
public interface ICustomValues {
....
}
public class MySpecificClass : ICustomValues {
....
}
public abstract class MyAbstract<T> where T : ICustomValues {
public abstract T CustomValues {
get;
set;
}
}
public class MyImplementation: MyAbstract<MySpecificClass> {
public override MySpecificClass CustomValues { get; set; }
}
Thanks to you all guys. I found the solution by using a generic properly:
public abstract class MyAbstract<T> {
public abstract T CustomValues { get; set; }
}
public class MyImplementation : MyAbstract<MySpecificClass> {
public override MySpecificClass CustomValues { get; set; }
}
I couldn't find the answer in the internet so I gonna ask for your help.
I have an abstract class:
public abstract class AbstractClass
{
String Name { get; }
}
Child Class 1:
public class ApplicationDetailsModel : AbstractClass
{
// This will implement unique properties
}
And each class that implements IComponent will implement a child of "AbstactClass".
An example implementation:
public class ExampleClass : IComponent
{
public ApplicationDetailsModel DetailsModel;
}
And an interface
public interface IComponent : IPageViewModel
{
AbstractClass DetailsModel { get; }
}
This example does not compile because the interface forces to implement
AbstractClass DetailsModel = new ApplicationDetailsModel();
Is there a correct way to force an implementation of a child property of a specific abstract class in an interface?
Make your interface generic with a constraint
public interface IComponent<T> : IPageViewModel
where T : AbstractClass
{
T DetailsModel {get;}
}
By example:
public class ExampleClass : IComponent<ApplicationDetailsModel>{
{
public ApplicationDetailsModel DetailsModel { get; private set; }
}
I'm changing a class from public abstract AwesomeClass, to public sealed AwesomeClass. I've also added a new property. All existing members are unchanged. I know that this is a breaking change. Clients that have implemented AwesomeClass or relied on it being abstract via reflection will be broken.
My question is, will clients that have only used members of instances of AwesomeClass that I've provided, be broken (and if yes how)? None of the clients will have a dependency on any of my types that implemented AwesomeClass as they were all internal. I think not, but...
Here is the class before and after:
public abstract class AwesomeClass
{
public abstract Guid SuperGuid { get; set; }
public abstract int SuperInt { get; set; }
}
public sealed class AwesomeClass
{
public Guid SuperGuid { get; set; }
public int SuperInt { get; set; }
public int OtherSuperInt { get; set; }
}
You mean that when you have this:
public abstract class Foo
{
public string Bar;
}
void UpdateFooBar(Foo foo)
{
foo.Bar = "Updated";
}
And you change abstract class Foo to sealed class Foo, will UpdateFooBar(Foo foo) continue to work?
What kept you from trying? But yes, it will.