CODEWITHSUNDEEP
c#oop
wenn32
wenn32

Reputation: 1382

which makes sense for this case - class vs interface vs abstract?

I have a "Package" table in database.

A Package can be of three types: Package A, Package B and Package C.

All the three package have some common fields like
1)name
2)size
3)weight

Now coming to the unique fields:

Package A & B must contain -
a)channel

Package C must contain -
a)completion

So, I create a table called as "Package" in database.
Columns of "Package" then would be:

1)id
2)type (1 = PackageA, 2 = PackageB, 3 = PackageC)
3)name
4)size
5)weight
6)channel (not required for Package C)
6)completion (not required for Package A & B)

So, I create an abstract class like below (ignoring datatypes of the properties):

public abstract class Package
{
public id;  
public type;
public name;  
public size;    
public weight;  
}

public class PackageA : Package
{
public channel;
}


public class PackageB : Package
{
public channel;
}

public class PackageC : Package
{
public completion;
}

what would I be doing wrong with this approach? Should the Package class be abstract or simply class?
Since I would not want other to work directly on Package class and instead take on Package A,B,C.

EDIT: What about the database part? Is it common to have fields/column like "channel"(needed for Package A & B) (not needed for Package C) and "completion"(needed for Package C)(not needed for Package A & B) to have "null" when not needed/used for specific package type?

Upvotes: 4

Views: 77

Answers (1)

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726579

The only thing that's wrong with this approach is that channel is duplicated across PackageA and PackageB. You could fix it by adding another base class for the two package types that share a channel:

public abstract class PackageWithChannel : Package {
    public Channel Channel {get;set;}
}
public class PackageA : PackageWithChannel {
   ...
}
public class PackageB : PackageWithChannel {
   ...
}

This eliminates duplication of the Channel property.

As for the database part, there are different ways of mapping a class hierarchy to an RDBMS, ranging from a single table for attribute-value lists to a table-per-hierarchy with a type field. You picked a table-per-hierarchy, which is entirely valid.

Upvotes: 2

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