I'm having trouble trying to implement a shared method/property between two classes created by the linq2sql designer.
My two classes have two main properties (coming from the db model):
public partial class DirectorPoll
{
public bool Completed {get; set;}
public bool? Reopen { get; set; }
//more properties
}
public partial class StudentPoll
{
public bool Completed {get; set;}
public bool? Reopen { get; set; }
//more properties
}
Now for example I create an abstract class:
public abstract class GenericPoll
{
public abstract bool Completed { get; set; }
public abstract bool? Reopen { get; set; }
public bool CanEdit
{
get
{
if (Completed == false) return true;
if (Reopen.GetValueOrDefault(false) == false) return false;
return true;
}
}
}
Then
public partial class DirectorPoll : GenericPoll
public partial class StudentPoll: GenericPoll
But when I try to compile it says "Director does not implement inherited abstract member GenericPoll.Completed.get". But it is there. So I think I'm forced to put an override to the property automatically generated by the designer, but if I update the database later and recompile it will give me the same error.
I think I might be missing something here but I've tried different approaches with no success. ¿So what can I do here, besides implementing CanEdit in each of my partial classes? Thanks
It isn't implemented as an override, so it doesn't count. However, implicit interface implementations do count, so this works:
partial class DirectorPoll : IGenericPoll {}
partial class StudentPoll : IGenericPoll {}
public interface IGenericPoll
{
bool Completed { get; set; }
bool? Reopen { get; set; }
}
public static class GenericPoll {
public static bool CanEdit(this IGenericPoll instance)
{
return !instance.Completed || instance.Reopen.GetValueOrDefault();
}
}
One option: create an interface containing Completed and Reopen, make the classes implement the interface (via the manual bits of the partial classes), then write an extension method which extends that interface. I think that should work:
public interface IPoll
{
bool Completed {get; set;}
bool? Reopen { get; set; }
}
// Actual implementations are in the generated classes;
// no need to provide any actual code. We're just telling the compiler
// that we happen to have noticed the two classes implement the interface
public partial class DirectorPoll : IPoll {}
public partial class StudentPoll : IPoll {}
// Any common behaviour can go in here.
public static class PollExtensions
{
public static bool CanEdit(this IPoll poll)
{
return !poll.Completed || poll.Reopen.GetValueOrDefault(false);
}
}
Admittedly then it has to be a method rather than a property, as there's no such thing as an extension property, but that's not too much of a hardship.
(I believe my refactoring of your logic in CanEdit is correct. All those explicit trues and falses were doing my head in ;)
Related
In my ASP.NET Core API, I have a DTO class BaseBDto and another DerivedBDto that inherits from it, and hides some of its properties, because they're required in DerivedBDto. The properties of BaseBDto and DerivedBDto are objects of another classes, BaseADto and DerivedADto respectively, that follow the same logic as the first ones. I also have a BaseModel class to which both BaseBDto and DerivedBDto will be mapped through another class Mapper.
Something like the following code:
using System.ComponentModel.DataAnnotations;
public class BaseADto
{
public string Name { get; set; }
}
public class DerivedADto : BaseADto
{
[Required]
public new string Name { get; set; }
}
public class BaseBDto
{
public BaseADto A { get; set; }
}
public class DerivedBDto : BaseBDto
{
[Required]
public new DerivedADto A { get; set; }
}
public class BaseModel
{
public string NameModel { get; set; }
}
public static class Mapper
{
public static BaseModel MapToModel(BaseBDto dto) => new BaseModel
{
NameModel = dto.A.Name
};
}
But it turns out, when passing a DerivedBDto object to the MapToModel method, it's trying to access the values of the BaseBDto (which are null) instead of the DerivedBDto ones.
Is there any way I can achieve this behavior?
I can only think of declaring BaseBDto as abstract, but that would prevent me from instantiating it, which I need to do.
PS: I already asked a similar question here, but I oversimplified my code sample, so I felt another question was necessary.
Also, the solution provided there doesn't work because I can't override the A property at DerivedBDto with a DerivedADto since it must have the same type as the A property at BaseBDto.
Have you tried changing the MapToModel signature to be generic. The below
public static BaseModel MapToModel<T>(T dto) where T : BaseBDto => new BaseModel
{
NameModel = dto.A.Name
};
I have a base class for all the ENTITIES of my project which is inheriting from below model :
public class BaseModel
{
public int Id { get; set; }
public int CreatedDate { get; set; }
public override string ToString();
}
Now I have 1 another functionality which is common for so many modules and I want to keep BaseModel for that functionality and want it to be inherited from it.
Public class BaseNotice
{
// Common info related to notice which is use to send notice to employees in different scenarios
}
Now our every model is suppose to inherit from BaseModel so inheriting from BaseNotice will be multiple inheritance.
Now I cannot like below :
Public class BaseNotice : BaseModel
{
// Common info related to notice which is use to send notice to employees in different scenarios
}
Because I would like to control functionality related to Notice from BaseNotice model and for notice I would like to keep BaseNotice as base model.
But I am not getting how to avoid multiple inheritance here and so what would be the proper way to design this?
There is No need to Multiple Inheritance. you can do that in this way:
public class BaseModel
{
public int Id { get; set; }
public int CreatedDate { get; set; }
public override string ToString();
}
public interface IBaseNotice
{
// Base Notices Contracts should be placed here
}
Public class BaseNotice: IBaseNotice
{
// Common info related to notice which is use to send notice to employees in different scenarios
}
public class ModelX:BaseModel
{
public IBaseNotice Notice { get ; set; }
public ModelX(IBaseNotice baseNotice)
{
Notice = baseNotice;
}
}
Or you can use Second Generation of your BaseModel:
public class BaseModeNoticable:BaseModel
{
public IBaseNotice Notice { get ; set; }
public BaseModeNoticable(IBaseNotice baseNotice)
{
Notice = baseNotice;
}
}
It is clearly explained here how to achieve "multiple inheritance" in C# by using Interface. However, I wonder, how to achieve the same but in the Entity Framework Code First Workflow.
Provided code to make things clear :
public abstract class DomainObject {
// Every business model must have this fields
public Guid Id {get;set;}
public string SystemCode {get;set;}
}
And here also some optional abstract classes like:
public abstract class MultiTitleObject : DomainObject {
public string TitleRu { get; set; }
public string TitleEn { get; set; }
}
public abstract class ManageableByAdminObject : DomainObject {
public bool isVisibleOnSite {get;set;}
public bool isDeletedByAdmin {get;set;}
}
Let's say that I have class that need to have fields of both MultiTitleObject and ManageableByAdminObject and DomainObject as always rule.
Since C# doesn't support multiple inheritance, I can do the following :
public class ManageableByAdminDomainObject : ManageableByAdminObject {
}
public class ManageableByAdminMultiTitleDomainObject : ManageableByAdminDomainObject {
// Even here it's too complicated...
// What if I need to inherit from 3 or more classes?
}
So the solution I wanted to use is Interface like :
public interface IFieldImitation {
bool isVisibleOnSite ();
}
public class ManageableByAdminObject : IFieldImitation, DomainObject {
public bool isVisibleOnSite () => return true;
}
However, EF does understand abstract classes but not the interfaces.
How should I solve this problem?
Say I've got a simple inheritance chain where Employee is the abstract base class and Checkout and Manager inherit from it in this purely illustrative console app. Now I want to have a method that will take in an object of type Manager or Checkout and return an integer amount of a bonus depending on the position in the company of the employee. I had some initial thoughts on doing this, and would like to know potential long-term deficits or gains from each approach if this console app were to one day grow up to be a data-driven web application.
Use an interface common to the inherited classes.
My base class looks like
abstract class Employee
{
public int EmployeeId { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
}
and my derived classes implement an interface designed to print employee information to the console called IPrintable and only has one method to do so. Although this interface has nothing to do with giving bonuses I mocked up the following in the class with my Main method lives and the program runs fine.
static int GiveBonusesViaInterface(IPrintable i)
{
if (i is Checkout)
return 1000;
else
return 2000;
}
It seems to me that if I wanted to use an interface for this I should probably make another one specific to giving raises instead of riding the coattails on an already-implemented interface (but that's another question for another day).
Use a static method in the base class like
public static int GiveBonus(Employee e)
{
if (e is Manager)
return 2000;
else
return 1000;
}
Make an abstract method in the abstract base class and nave derived classes implement as they see fit
abstract class Employee
//fields and constructors
{
public abstract int GiveBonusesViaAbstractMethod(Employee e);
}
This seems to be the worst idea to me because there will have to be a method in each derived class that takes in a parameter of IPrintable or Employee type and in the Manager class we'd have to test if the employee is-a Manager.
Are 1-2 equally as scalable and managable for a long-term web application? Is option 3 really as bad as I made it out?
You're missing the traditional OO way of doing this:
abstract class Employee {
public int EmployeeId { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public abstract int GetBonusAmount();
}
class Manager : Employee {
public override int GetBonusAmount() { return 2000; }
}
class Checkout : Employee {
public override int GetBonusAmount() { return 1000; }
}
Console.WriteLine(someEmployee.GetBonusAmount());
I think you really have already answered your own question.
my derived classes implement an interface designed to print employee information to the console called IPrintable and only has one method to do so. Although this interface has nothing to do with giving bonuses
[emphasis mine]
You already have an interface for this. It's called Employee. The idiomatic way to do to this is to implement a virtual method on your abstract class and override if necessary. The more idiomatic C# approach is to write a property and override it. Like so:
abstract class Employee {
public virtual int GetBonus()
{
return this.Bonus;
}
public virtual int Bonus { get; set; }
}
class Manager : Employee {
public override int Bonus
{
get { return 2000; }
}
}
class Checkout : Employee {
public override int Bonus
{
get { return 1000; }
}
}
Implement a GetBonus() method in both the subclasses. You should avoid doing "is instance of" checks altogether.
I think abstract works well :
abstract class Employee
{
public int EmployeeId { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public abstract int GetVariableBonus();
}
class Manager {
public int GetVariableBonus(){
return 2000;
}
}
class Employee{
public int GetVariableBonus(){
return 1000;
}
}
Is that what you need ?
I have a system that performs operations on lots of Things, these can be considered to be hardware devices accessible over a communication channel.
I use a manager construct that accepts tasks for single Things. Now, there are at least three types of Thing and they have slightly different properties associated with them. The manager must know about these extra properties as they are needed to perform any operation correctly (some Things must have their X foo'd instead of their Y etc...).
At the moment I have separate manager class for each type of thing. This causes a good deal of duplication as the Things are mostly similar.
It would be good if I could have an abstract manager that implements a good deal of the functionality and then each concrete implementation can supply the little extra bits.
Here is a greatly simplified example:
public abstract class ThingManager
{
private ConcurrentDictionary<Guid, ??ThingTask??> _ThingTaskQueue;
public virtual AddNewThingTask(<params>)
{
??ThingTask?? NewTask = new ??ThingTask??(<params>);
_ThingTaskQueue.Add(NewTask);
Monitor.Pulse(_NewDataToProcess);
}
/* Implemented by the concrete, will depend on the type of ??ThingTask?? */
public abstract GetSomeTaskParameterForAThing(Guid thingID)
}
public class ThingTask
{
public enum ThingOperation
{
Foo,
Bar
};
public String Name { get; set; };
public ThingType Type { get; set; };
public ThingOperation Operation { get; set; }
}
public class AdvancedThingTask
{
public enum ThingOperation
{
Foo,
Bar,
Baz
};
public String Name { get; set; };
public ThingType Type { get; set; };
public ThingOperation Operation { get; set; }
public Boolean EnableFrobber { get; set; }
}
As you can see I need some way, when defining the concrete ThingManager to have ??ThingTask?? be either a ThingTask or an AdvancedThingTask. It would then be up to the concrete to make use of the extra properties when implementing the abstract methods.
Using an interface for ??ThingTask?? wouldn't work because the properties would have to be declared in the interface and each one has different properties available.
I get the feeling I'm missing something very obvious as to how to do this cleanly, hopefully someone can help :)
use generics rather than a pure abstract class, someting along the lines of:
public abstract class ThingManager<T> where T : ThingTask
dependant on your full implementation I doubt if this will need to remain abstract
Is there any reason you don't make AdvancedThingTask a subclass of ThingTask?
public class ThingTask
{
public virtual string Name { get; set; }
public virtual ThingType Type { get; set; }
public virtual ThingOperation Operation { get; set; }
public virtual void DoThing() { /*Do something associated with ThingTask*/ }
}
public class AdvancedThingTask : ThingTask
{
public bool EnableFrobber { get; set; }
public override void DoThing() { /*Do something associated with AdvancedThingTask*/ }
}
The only problem I see with this is that ThingOperation will need to be declared outside of the classes so that it can have all the values, or some other solution that will enable classes to have values that aren't in the base declaration. That problem may be solved by putting what you want to do as virtual methods in the classes.
P.S. Why do your properties start with underscores? Usually that's reserved for private variables.