I'm trying to implement the best code re-usability. The problem is that I can't access the base method located in the Base Abstract class form the Main Program through the repository.
If you go through the example below you will see a sample code of my situation.
So my question is how can I access methods located in the base abstract class from the main program.
Classes/Interfaces
public abstract class BaseEntity
{
public override abstract String ToString();
}
public abstract class BaseClass<T> where T : BaseEntity
{
public T GetById(int id)
{
//Dummy Code
return new T();
//
}
}
public interface IFooRepository
{
IList<Foo> GetOrderedObjects();
}
public interface FooRepository : BaseClass<Foo>, IFooRepository
{
public IList<Foo> GetOrderedObjects()
{
//GetById method is accessible from the repository - Fine
var obj = this.GetById(5);
//Dummy Code
return new List<Foo>();
//
}
}
//Main App
public class void Main()
{
private IFooRepository _fooRepository;
public void ProgramStartsHere()
{
//This is ok.
var list = _fooRepository.GetOrderedObjects();
//Problem is here - GetById method is not accessible from the main program through the FooRepository
var obj = _fooRepository.GetById(10);
}
}
GetById isn't defined in the interface
I would make an
public interface IBaseRepository<T> where T : BaseEntitiy {
T GetById<T>(int id);
}
Then BaseClass implements IBaseRepository<T>
and IFooRepository inherits from IBaseRepository<Foo>
EDIT :
A full example, similar to #Olivier J-D one, with idea (maybe wrong), that GetOrderedObject may be same for all your entities.
public abstract class BaseEntity
{
public override abstract String ToString();
}
//all generic methods
public interface IRepositoryBase<T>
where T : BaseEntity, new()
{
T GetById(int id);
IList<T> GetOrderedObjects();
}
//all methods specific to foo, which can't be in a generic class
public interface IFooRepository :IRepositoryBase<Foo>
{
void Update(Foo model);
}
//implementation of generic methods
public abstract class BaseClass<T> : IRepositoryBase<T>
where T : BaseEntity, new() // ===> Add new() constraint here
{
public T GetById(int id)
{
return new T();
}
public IList<T> GetOrderedObjects() {
var obj = this.GetById(5);
//Dummy Code
return new List<Foo>();
//
}
}
//implementation of Foo specific methods
public class FooRepository : BaseClass<Foo>, IFooRepository
{
public void Update(Foo model) {
//bla bla
}
}
Add a new Interface which declares the GetById method and let IFooRepository and BaseClass<T> inherit from it. You will have to add a generic type parameter to IFooRepository as well. (I renamed IFooRepository to IRepository<T>, since it is generic now.)
public abstract class BaseEntity
{
public override abstract String ToString();
}
public interface IRetriever<T>
where T : BaseEntity, new()
{
T GetById(int id);
}
public interface IRepository<T> : IRetriever<T>
where T : BaseEntity, new()
{
IList<T> GetOrderedObjects();
}
public abstract class BaseClass<T> : IRetriever<T>
where T : BaseEntity, new() // ===> Add new() constraint here
{
public T GetById(int id)
{
return new T();
}
}
public class FooRepository : BaseClass<Foo>, IRepository<Foo>
{
public IList<Foo> GetOrderedObjects()
{
var obj = this.GetById(5);
return new List<Foo>();
}
}
This will work fine then
IRepository<Foo> _fooRepository = new FooRepository();
var list = _fooRepository.GetOrderedObjects();
var obj = _fooRepository.GetById(10);
Your _fooRepository inherits from IFooRepository, not FooRepository, so it doesn't have access to GetById(10);
You must expose the GetById method in your repository interface.
public interface IFooRepository
{
IList<Foo> GetOrderedObjects();
Foo GetById(int id);
}
Alternatively you can use a type parameter constraint, as stated by Raphaël Althaus
IFooRepository doesn't inherit from BaseClass, so you have to cast _fooRepository to FooRepository. Then you can access GetById()
Cast it to the base class.
var obj = ((BaseClass<Foo>)_fooRepository).GetById(10);
Related
I don't want to make class B generic because there lots classes inheriting from class B. How to use the method "GetSomeData" of the generic class "classA" in a non generic class?
Here's my code:
public abstract class classA<T> : IInterface<T>
where T : new()
{
public String GetSomeData (Guid ID)
{
return somestring;
}
}
public abstract class ClassB : InterfaceB
{
//Use GetSomeData(Guid ID) here
}
what is the best way to invoke GetSomeData in class B?
First of all, your code doesn't look clean itself. C# coding conventions are not met & not all the components that are used present.
But to anser your question, you need to specify the concrete type T before using generic methods/classes.
For example working code may look like this:
public abstract class GenericParent<T>
where T : new()
{
public string GetSomeData(Guid id) => string.Empty;
}
// Non abstract type, to create be able to create an instance
public class GenericChild<T> : GenericParent<T> where T : new()
{
}
public abstract class ClassB
{
public void DoSomething()
{
// Creating instance of a generic type, specifying concrete T (in this case of type SomeClass)
var instance = new GenericChild<SomeClass>();
instance.GetSomeData(Guid.Empty);
}
}
// An example of type, that meets the "where" condition of T in the generic type
public class SomeClass
{
}
As per OOP principals Abstract classes can not be instantiated.
They could only be Inherited. Well there are couple of ways how you can access the instance variables and methods from the Abstract class as follows.
Make a sub-class inheriting the Abstract class; Create an object of sub-class and access all the Instance Variables and Methods.
public abstract class classA<T> : IInterface<T>
where T : ITask, new()
{
public String GetSomeData (Guid ID)
{
return somestring;
}
}
public class ChildOfClassA : ClassA<SomeType_of_Type_ITask>
{
}
public abstract class ClassB : InterfaceB
{
//Use GetSomeData(Guid ID) here
ChildOfClassA obj = new ChildOfClassA();
string result = obj.GetSomeData(Guid.NewGuid());
}
Make that method Static if its not tightly coupled to instance of the class. and then you can use it with ClassName.MethodName
public abstract class classA<T> : IInterface<T>
where T : ITask, new()
{
public **static** String GetSomeData (Guid ID)
{
return somestring;
}
}
public abstract class ClassB : InterfaceB
{
//Use GetSomeData(Guid ID) here
string result = classA.GetSomeData(Guid.NewGuid());
}
You can inherit this Abstract class in the class you want to use it and directly access it by base.MethodName or directly MethodName.
public abstract class classA<T> : IInterface<T>
where T : ITask, new()
{
public string GetSomeData (Guid ID)
{
return somestring;
}
}
public abstract class ClassB : ClassA<SomeType_of_Type_ITask>, InterfaceB
{
//Use GetSomeData(Guid ID) here
string result = [base.]GetSomeData(Guid.NewGuid()); //[base.] is optional even you can override this function or overload it.
}
In case 1 and 3 you will have to pass generic argument in order to inherit the Abstract class as in your case Abstract class accepts generic arguments.
I have the following interface
public interface IInterface
{
int GetId();
}
ClassA is a generic class but T should implement IInterface
public class ClassA<T> where T : IInterface {
}
ClassB implements IInterface
public class ClassB : IInterface {
public int GetId() {
return 1;
}
}
ClassC is where my problem is, namely adding items to the list.
public class ClassC {
List<ClassA<IInterface>> list = new List<ClassA<IInterface>>();
public void Add<T>(ClassA<T> item) where T : IInterface {
list.Add(item);
}
}
The code above gives the following error which makes sense
cannot convert from 'Program.ClassA<T>' to'Program.ClassA<Program.IInterface>'
The core of the problem is in the Add() method where my goal is to be able to add any type of ClassA. I am not sure how to design this in order to achieve the following
ClassC classC = new ClassC();
ClassA<ClassB> classA = new ClassA<ClassB>();
classC.Add(classA);
Any ideas?
What about using Covariant Generic Type Argument.
public interface IInterface
{
int GetId();
}
// Contra-variant and covariant generic type argument can be used only in interfaces and delegates
public interface IClassA<out T> where T : IInterface
{
}
public class ClassA<T> : IClassA<IInterface> where T : IInterface { }
public class ClassB : IInterface
{
public int GetId()
{
return 1;
}
}
public class ClassC
{
List<IClassA<IInterface>> list = new List<IClassA<IInterface>>();
public void Add(IClassA<IInterface> item)
{
list.Add(item);
}
}
public class Test
{
public static void Run()
{
ClassC classC = new ClassC();
ClassA<ClassB> classA = new ClassA<ClassB>();
classC.Add(classA);
}
}
Depending on the specifics of your design, you may be able to split ClassA in two:
public abstract class ClassA {
//Stuff that only works in terms of IInterface,
//maybe with some abstract methods, required constructors, etc
}
public class ClassA<T> : ClassA where T : IInterface {
//Stuff specific to T
}
You then store ClassAs in your list and cast them to their known concrete type as/when you know what that is and need to work in those terms (e.g. to be able to call ClassA<T> specific functionality)
I am encountering a problem with interfaces. I wish to chain a method which derives its chainable method from an abstract class, which implements an interface.
public interface IBaseInterface {
public IBaseInterface ChainableMethod()
}
public abstract AbstractClassThatHelps<T> where T: IBaseInterface n {
public T ChainableMethod() {
return (T) this;
}
}
public interface IDerived : IBaseInterface { }
public class DerivedClass : AbstractClassThatHelps<IDerived>, IDerived { }
IDerived derived = new DerivedClass();
derived.ChainableMethod().ChainableMethod();
The problem I face here: why can't T be returned when it is shown to implement the contract IModel?
How would I solve this differently? I wish to have type safety but I am forced for all derived classes to return IBaseInterface instead of their own interface.
Actual implementation:
We have multiple models (DerivedClass's) which implement their respective IDerived for dependency injection. These need helpers because i dont want to repeat myself.. So we use AbstractClassThatHelps as a base, but because we are dealing with chainable methods we need this base class to know what to return, so therefore generics. IBaseInterface can be seen as IModel. Where ChainableMethod can be seen as GetAll() for example.
In order for the following code to work AbstractClassThatHelps<T> must implement IBaseInterface. How can you return this, if this is not IBaseInterface
public abstract AbstractClassThatHelps<T> where T: IBaseInterface n{
public T ChainableMethod(){
return this;
}
}
Edit: I am not user what this design solves but here is my attempt at what you are trying to achieve→
public interface IBaseInterface
{
IBaseInterface ChainableMethod();
}
public abstract class AbstractClassThatHelps<T>:IBaseInterface where T : IBaseInterface{
public T ChainableMethod()
{
IBaseInterface i = this;
return (T)i.ChainableMethod();
}
IBaseInterface IBaseInterface.ChainableMethod()
{
return this;
}
}
public class Concrete : AbstractClassThatHelps<Concrete>
{
}
You can return an instance of T, but the return type cannot be T but must be IBaseInterface because that is what the interface requires.
This is working, your code was full of syntax errors:
public interface IBaseInterface
{
IBaseInterface ChainableMethod();
}
public abstract class AbstractClassThatHelps : IBaseInterface
{
public IBaseInterface ChainableMethod()
{
return this;
}
}
public interface IDerived : IBaseInterface
{
}
public class DerivedClass : AbstractClassThatHelps, IDerived
{
}
internal static class Program
{
public static void Main()
{
IDerived derived = new DerivedClass();
derived.ChainableMethod().ChainableMethod();
}
}
you could also try this:
public interface IBaseInterface
{
IBaseInterface ChainableMethod();
}
public abstract class AbstractClassThatHelps<T> : IBaseInterface where T : class, IBaseInterface
{
public T ChainableMethod()
{
return this as T;
}
IBaseInterface IBaseInterface.ChainableMethod()
{
return ChainableMethod();
}
}
public interface IDerived : IBaseInterface
{
IDerived Hello();
}
public class DerivedClass : AbstractClassThatHelps<IDerived>, IDerived
{
public IDerived Hello()
{
Console.WriteLine("Hello");
return this;
}
}
internal static class Program
{
public static void Main()
{
AbstractClassThatHelps<IDerived> derived = new DerivedClass();
derived.ChainableMethod().Hello().ChainableMethod();
}
}
Because i don't know how to explain my problem clearly,i give an example!
I have these Interfaces and classes:
public interface IParam
{
....
}
public class Param1:IParam
{
....
}
public class Param2:IParam
{
....
}
public interface IParamDbService<TEntity> where TEntity : IParam
{
IQueryable<TEntity> GetAll();
}
public class Param1DbService : IParamDbService<Param1>
{
public IQueryable<Param1> GetAll()
{
...
}
}
public class Param2DbService : IParamDbService<Param2>
{
public IQueryable<Param2> GetAll()
{
...
}
}
And in some cases i need to do this:
IParamDbService<Param> paramDbService;
IParamDbService<Param1> param1DbService;
IParamDbService<Param2> param2DbService;
paramDbService=param1DbService; or paramDbService=param2DbService;
I use paramDbService in my code so sometimes i need to copy param1DbService into it and the othertime param2DbService.but they have different type so i can't do that.Any ideas?
Make it covariant (note the out TEntity):
public interface IParamDbService<out TEntity> where TEntity : IParam
{
IQueryable<TEntity> GetAll();
}
IParamDbService<IParam> paramDbService;
IParamDbService<Param1> param1DbService;
paramDbService=param1DbService
If you add other methods to the DbService, which get TEntity as argument, it is not covariant anymore. You need to split the interface into a DbReader<out TEntity> with only the reading part and and DbService<TEntity> with everything else.
Alternatively, you could make the writing members based on IParam to make them covariant as well.
I have read a bit about constraints and am trying to implement it in my repository pattern.
I want something like the below but can't quite get it to compile.
public interface IRepository<T>
{
void GetAllData<T>();
}
//This needs to inherit from IRepository
//T has to be a model class
//V has to be a class that implements IEmployeeRepo
public interface IEmployeeRepo<T, V> where V : EmployeeRepo where T : class : IRepository<T>
{
void DoSomethingEmployeeRelated();
}
//Dont think this inheritance is correct
public class EmployeeRepo<Employee, this> : IEmployeeRepo
{
}
//My example model class
public class Employee
{
public string Name {get;set;}
}
Not sure why you have two type parameters on the Repository - what is the point?
*Here is the classic example of a .NET Repository using Generics: *
*First, the Repository Interface: *
public interface IRepository<T> where T : class
{
T FindSingle(Expression<Func<T,bool>> predicate);
IQueryable<T> FindAll(); // optional - matter of preference
void Add(T entity);
void Remove(T entity);
}
*Second, the Generic Repository Implementation (EF as the example): *
public abstract class GenericRepository<T> : IRepository<T>
{
private IObjectSet<T> _ObjectSet; // get this in via DI (for example)
public T FindSingle(Expression<T,bool>> predicate)
{
return _ObjectSet.SingleOrDefault(predicate);
}
// you can figure out how to do the other implementation methods
}
*Then, the Specific Repository (you should have one per aggregate root, and also an interface for each specific repository detailing specific methods): *
public EmployeeRepository : GenericRepository<Employee>, IRepository<Employee>
{
// all regular methods (Find, Add, Remove) inherited - make use of them
public Employee FindEmployeeByName(string name)
{
return FindAll().SingleOrDefault(x => x.Name == name);
// or you could do: return FindSingle(x => x.Name == name);
}
}
Usage:
IRepository<Employee> repository = new EmployeeRepository<Employee>();
Don't go out looking to go too crazy with generics - the only one you need is to constrain the Repository to be used by a entity that is encapsulated behind the Repository.
I simply use where T : class.
Other's use where T : IDomainAggregate or similar, to put constraints on the actual type of entity which is allowed.
In this situation i usually have a base repo class that implements IRepository<>, and is typed to a base Model class.
public interface IRepository<T> where T : IModel
{
void GetAll<T>();
void GetById<T>(int id);
}
public interface IEmployeeRepo<T> : IRepository<T> where T : IModel
{
void DoSomethingEmployeeRelated();
}
public class BaseRepo : IRepository<T> where T : IModel
{
public void GetAll<T>()
{
}
public void GetById<T>(int id)
{
}
}
public class EmployeeRepo : BaseRepo<Employee>, IEmployeeRepo<Employee>
{
public void DoSomethingEmployeeRelated()
{
}
}
//My example model class
public class Employee : IModel
{
public int Id {get;set;}
public string Name {get;set;}
}
Try this;
public interface IRepository<T>
{
void GetAllData<T>();
}
//This needs to inherit from IRepository
//T has to be a model class
//V has to be a class that implements IEmployeeRepo
public interface IEmployeeRepo<T, V> : IRepository<T> where V : EmployeeRepo where T : class
{
void DoSomethingEmployeeRelated();
}
//Dont think this inheritance is correct
public class EmployeeRepo : IEmployeeRepo<Employee, EmployeeRepo>
{
public void DoSomethingEmployeeRelated()
{
}
public void GetAllData<Employee>()
{
}
}
//My example model class
public class Employee
{
public string Name {get;set;}
}