I'm looking for a class structure or design pattern to implement a base class that has a list of "base items", where several derived classes have the same list but that list is of derived "base items".
Here's a vastly stripped down example (ignore the accessibility of properties, they wouldn't actually all have public setters and default constructors):
public class BaseTransaction {
public List<BaseTransactionItem> Items { get; set; }
public void AddItem(string description, int quantity, decimal price)
{
// Add a new BaseTransactionItem to Items
}
}
public class BaseTransactionItem {
public string Description { get; set; }
public int Quantity { get; set; }
public decimal Price { get; set; }
}
public class OrderTransaction : BaseTransaction {
public List<OrderTransactionItem> Items { get; set; }
public int Deposit { get; set; }
public void SetDeposit(int depositAmount)
{
// Do some stuff to set the deposit.
}
}
public class OrderTransactionItem : BaseTransactionItem
{
public int QuantityFulfilled { get; set; }
}
public class RetailTransaction : BaseTransaction {
public List<RetailTransactionItem> Items { get; set; }
public List<Tender> Tenders { get; set; }
public void AddTender(Tender tender)
{
// Add a tender to the RetailTransaction
}
public decimal TotalTax
{
get { return Items.Sum(i => i.Tax); }
}
}
public class RetailTransactionItem : BaseTransactionItem
{
public decimal Tax { get; set; }
}
The way I need to work with these classes is that you start with a BaseTransaction and add some items to it, and then it can become either an OrderTransaction or a RetailTransaction. These both share most of their logic and properties with a BaseTransaction but have specific extra fields and methods, as well as the List<BaseTransactionItem> becoming a List<OrderTransactionItem> or a List<RetailTransactionItem> respectively.
Further more, after a BaseTransaction is "promoted" to a RetailTransaction, it may be "demoted" back to a BaseTransaction and then "promoted" to an OrderTransaction (but never from a RetailTransaction to an OrderTransaction in this case).
I've tried several approaches to this, with generics, the Decorator pattern (which doesn't seem appropriate), TypeConverters, and yet nothing seems to fit. The only possible solution I've thought of that works is having the RetailTransaction class have a constructor that takes a BaseTransaction and copying over all the properties and converting the list using .Cast<RetailTransactionItem> but this will make maintaining the derived classes pretty difficult.
If it wasn't for the list type needing to change this would be a simple case of using inheritance. I'm completely open to alternative approaches such as those favouring composition over inheritance but since the RetailTransaction and OrderTransaction classes truely are more specific versions of BaseTransaction, inheritance seems to fit - at least in my mind.
Related
We are getting data for our application.
We have common set of data with common fields, PurchaseDate, Manufacturer, PurchaseAmount,
Then we have specific subclass (which contains specific vehicle info, Aircraft wingspan, or car miles/per gallon, or Boat floatation metrics.
Instead of having classes which are not required, how can we create a model with a specific data type?
public class VehicleInfo
{
public Datetime PurchaseDate { get; set; }
public string Manufacturer { get; set; }
public int PurchaseAmount { get; set; }
// specific data, not all these needed
public AircraftInfo AircraftInfo {get;set;}
public CarInfo Carinfo {get;set;}
public BoatInfo BoatInfo {get;set;}
}
I read Dependency injection is not ideal practice for DTOs? https://softwareengineering.stackexchange.com/a/83166/354368
You can choose from "is-a" (inheritance) or "has-a" (composition).
You already have what is common to all vehicles
public class VehicleInfo
{
public Datetime PurchaseDate { get; set; }
public string Manufacturer { get; set; }
public int PurchaseAmount { get; set; }
}
So you can use inheritance (and make VehicleInfo abstract)
public class AircraftInfo : VehicleInfo
{
...
}
or use composition
public class AircraftInfo
{
public VehicleInfo VehicleInfo { get; set; }
...
}
or mix composition and inheritance
public class PassengerAircraftInfo : AircraftInfo
{
public PassengerVehicleInfo PassengerVehicleInfo { get; set; }
...
}
If you have e.g. 5 out of 10 vehicles that shares a set of common properties in addition to common properties you already have, inheritance will require another abstract class that inherits from VehicleInfo. Composition will require a new property on each of the 5 vehicles.
What is best, depends on final result of your analysis for the project. Number of inheritance levels should be kept to a minimum in order to keep code complexity low.
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;
}
}
I have a generic class with a single argument that represents an Element of a third party DLL for the purpose of serialization of objects of T kind. What I would like to do is add a 'Dirty' map to my class and lazily trigger it whenever one of my Element's nested properties are changed.
Is it possible to when the property is accessed catch the request and identify what property is changing? That if a SET is being performed I can log that sub-property P is now dirty and needs to be saved? Or at least a single bit that indicates that SOMETHING has changed?
public class ResourceSerializer<T>
where T : Base, new()
{
T element;
Dictionary<String,Boolean> dirtyMap;
public T Element { get { return this.getElement(); } }
public Boolean IsDirty { get; private set; }
public ResourceSerializer()
{
dirtyMap = new Dictionary<string,bool>();
element = new T();
// code to reflect back upon T's Properties and build out the dirtyMap.
// I already can do this I just omitted it.
// in my Person example there would be keys: 'FirstName', 'LastName', 'Age', 'Gender', 'PrimaryAddress'
}
// how can I call this programmatically?
void flagDirty(String property)
{
dirtyMap[property] = true;
this.IsDirty = true;
}
T getElement()
{
// In case I need to do a thing before returning the element.
// Not relevant to the question at hand.
return this.element;
}
}
a somewhat advanced example of 'Base'. You can see how I need to recurse my actions as not everything is a primitive. I have a manager level class that logs all of these ResourceSerializer objects.
public class Base
{
public Base()
{
}
}
public enum gender
{
Male,
Female,
Other,
Unspecified,
}
public class Address : Base
{
public String Street { get; set; }
public String State { get; set; }
public String Zip { get; set; }
public Address() : base()
{
}
}
public class Person : Base
{
public String FirstName { get; set; }
public String LastName { get; set; }
public Int16 Age { get; set; }
public gender Gender { get; set; }
public Address PrimaryAddress { get; set; }
public Person() : base()
{
}
}
public class Patient : Person
{
public Person PrimaryContact { get; set; }
public Patient() : base()
{
}
}
and a small class i would turn into a test method later..
public class DoThing
{
public DoThing()
{
ResourceSerializer<Person> person = new ResourceSerializer<Person>();
person.Element.Age = 13; // catch this and mark 'Age' as dirty.
}
}
Without a custom setter no, there's nothing to do that.
The usual pattern for what you're trying to do is implement the INotifyPropertyChanged interface, that interface is precisely created for classes (or structs) which need to track and inform about changes on their properties.
If you're lazy as me, I would create an analyzer which at the beginning of my app scans all my classes which are tagged with an attribute and with all properties created as virtual, then using codedom I would create a new class which would inherit from the found class and it implements the INotifyPropertyChanged, then you can have a generic Factory which returns instances of these new classes when the type of the generic call is of a known registered type.
I've used this before for classes which I wanted to have remote properties, just tagged the class and my scan system rewrote the getter/setter to do the remote calls transparently, the concept at the end is the same.
It's a lot of work at the begining, but if you have a ton of classes it will be a lot less of code to write than implementing INotifyPropertyChanged on all your classes.
I have 5 Properties within my class that are all very similar; I want to group them. The class they are contained in used to look like this:
class Car
{
public string PropA { get; set; }
public string PropB { get; set; }
public string PropC { get; set; }
public Car() { }
}
So with Intellisense, I would be presented with:
Car car = new Car();
car.PropA
.PropB
.PropC
..I would be presented with the 3 properties. What I want is for it to be contained within it's own little group, so I would have to do:
car.Props.PropA = "example";
I created a partial class to hide them in, but I am not sure if this is the correct way to do it:
class Car
{
public Props { get; set; }
public Car() { }
}
partial class Props
{
public string PropA { get; set; }
public string PropB { get; set; }
public string PropC { get; set; }
}
Is there a better way to go about this? I ask because I am creating a class library and usability is very important.
The partial keyword is used to split a class's implementation among multiple files. Knowing that, it doesn't help (or hurt) in this situation.
Without knowing more about your design, your solution seems reasonable. Just get rid of the partial keyword, it's not appropriate here.
Agreed with what Patrick said. I had a question about your public setters though, and this is something I've been curious about how to handle myself.
if you're hoping for other people to use thing class (and assuming this wasn't just a mocked up example) are you sure you want people to just be able to willy nilly be able to set properties in your classes without going through a method/function that validates and/or handles the setting of the property?
this can be done like:
public class Props
{
public string PropA { get; private set; }
public string PropB { get; private set; }
public string PropC { get; private set; }
}
public Props() { }
public SetProps(string propA, string propB, string propC)
{
this.PropA = propA;
this.PropB = propB;
this.PropC = propC;
}
Now obviously doing something like this would depend on the nature of the requirements around the props (and this is an extremely simple example - all props have to be set at the same time). But with public setters a user of the class would not necessarily know the nature of the requirements, and the public setters could potentially allow them a way around how it was intended the class be used.
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.