Question

I am working on an application which currently creates data entity objects from the results of a sql query. In the database 3 of the tables are very similar but have several different properties.

My initial plan was to create 3 different classes, even though each class is very similar. However when I came to create the method which returns a list of objects, I have hit a stumbling block as the return type will be different depending on which mode the application is in.

e.g.

public class A
{
   public int Id {get;}
   public string Name {get;}
}

 public class B
 {
   public int Id {get;}
   public string Name {get;}
   public string ExtraInfo {get;}
 }


 public class MainScreen
 {
     ...
     this.resultsGrid.DataSource = LoadData();
 }

I would prefer not to write one method to load a list of each data type.
What should the return type of LoadData() be, to allow it to be generic as possible.

What is the most elegant way of dealing with this scenario?

Thanks,

Sean

Answer 1

You should have inheritance to allow polymorphism, so you would have a base class that all entities included in the data binding derive from it.

Then, you can have a mid-base class to have some shared properties like Name and ID.

Base class:

public abstract class Entity
{
}

Entity with Name and ID:

public class NameAndIDEntity : Entity
{
    public int Id { get; set; }
    public string Name { get; set; }
}

Entity with Name, ID and ExtraInfo:

public class NameIDAndExtraEntity : NameAndIDEntity
{
    public string ExtraInfo { get; set; }
}

Entity with other information (can’t be derived from NameAndIDEntity), derives from Entity so it can be included in the data binding:

public class OtherInformationEntity : Entity
{
    public int Age { get; set; }
}

Finally, you can make the LoadData return type Entity.