Question

I’m new to .net and OOP and I’ve been having difficulty working out how I should create classes for a property site I’m building.

In my database, I have a “House” table with various fields.

Sometimes, a house may have a garden, or garage, a pool etc, so I have separate tables to store the data on each of these, all connected to the “House” table’s unique identifier.

In my code, I have created a “House” class, but how do I then define classes for the other tables?

I could obviously have a “Garden” class, which would inherit the “House” class, but, depending on a visitor’s selections, I may sometimes need to display data on (for example) the house, the garden and the garage and I can’t see how this method would work. I could just have one big class that defines the house, the garden, the garage and so on and leave lots of nulls when something isn’t needed, but I’m pretty sure that can’t be the correct approach!

I’ve been struggling with this all day, so any info is very much appreciated!

Answer 1

House class may have a collection of features.

You can basicly create an abstract base class called “Feature” or an interface called “IFeature” and inherit/implement it to the class that is meant to be a feature (i.e. Garden).

Then all you need to do is creating a collection in House class called “Features”.
Here is an example interface in C#:

interface IFeature
{
    // Properties or methods you want all the features to have.

    decimal Price { get; }
}

Your feature classes need to implement IFeature interface.

class Garden : IFeature
{
    // This property is needed to implement IFeature interface.
    public decimal Price { get; private set; }

    public Garden(decimal price) { Price = price; }
}

To implement IFeature, a class must have a decimal property called “Price” with a get accessor like the Garden class above and the Pool class below:

class Pool : IFeature
{
    public decimal Price { get; private set; }
    public float Depth { get; private set; }

    public Pool(decimal price, float depth) { Price = price; Depth = depth; }
}

House class should have a collection of IFeature instead of Pool or Garden:

class House
{
    public List<IFeature> Features { get; private set; }

    public House()
    {
        Features = new List<IFeature>();
    }
}

Then, you can add features to a house like this:

House h = new House();

h.Features.Add(new Garden(6248.12m));
h.Features.Add(new Pool(4830.24m, 10.4f));

And using LINQ, you can,

// Check whether the house has a garden:
h.Features.Any(f => f is Garden);

// Get the total cost of features.
h.Features.Sum(f => f.Price);

// Get the pools that are deeper than 5 feet.
h.Features.OfType<Pool>().Where(p => p.Depth > 5f);

// etc.

More information about interfaces.
More information about LINQ.