C# 3-Layer architecture insert to database with dependency injection in mind

Question

Let's just say I have a transaction form in which I can choose a specific customer and that customer's order details.

So I'll be having :

Customer.cs

public class Customer
{
    public string Id { get; set}
    public string Name { get; set}
}

Goods.cs

public class Goods
{
    public string Id { get; set}
    public string Description { get; set}
    public string Price { get; set}
}

Order.cs

public class Order
{
    private List<Goods> _orderedGoods = new List<Goods>();

    public string Id { get; set}
    public Customer Customer { get; set}
    public List<Goods> OrderedGoods { get; }

    public void AddGoods(Goods goods)
    {
        _orderedGoods.Add(goods);
    }
}

And then in the presentation layer, I have a gridview which only consists of goods id string.

My questions are these :

Is it okay if I let Order class create it's own detail? Or should it be property injected as well?
When I wanted to save my order form, should Presentation layer or Business layer who populates the Order detail?
If Business layer only sends a complete object for repository to save, then Business layer should be able to create a new Order object? Or is there another way to manage transient object creation with DI in mind?

Sorry for the long question, really need help with this.

Thank you !

Fendy · Accepted Answer · 2013-05-04 07:22:56Z

1

It is quite subjectical, but for me:

Is it okay if I let Order class create it's own detail? Or should it be property injected as well?

What do you mean by create it's own detail? A new detail object should has an input (from UI) or should be retrieved from a storage (repository). That way, I prefer to keep the Detail to be injected instead of created in the Order class; and being created in the UI or repository, or a business class responsible for it.

When I wanted to save my order form, should Presentation layer or Business layer who populates the Order detail?

It depends, whether the creation of Order detail object has specific rule or not. If not, then I prefer to create the Order class with the detail, and let the Business Layer do the validation. If it need a specific logic (such as you set value A to property A, if value 1 is set to property B), keep it in business logic, or create a builder pattern for it.

If Business layer only sends a complete object for repository to save, then Business layer should be able to create a new Order object? Or is there another way to manage transient object creation with DI in mind?

It is the same as my answer above. The main point of dependency injection is to keep the logics in such a modular way, so it can be reused, and standardized. If you think it is need a specific-reuseable logic in object creation (Detail) then you need to create a Service object for it. Otherwise, it is better to leave the creation in other layer (UI).

Other things to note:

Are you really sure to use List<T> as Detail data type? It will limit the implementation of detail object to a mere List<T>. If sometimes the logic want to use Array instead, it will need another configuration to the object. I prefer to use IEnumerable<T> instead and use List<T> in private if I need to do on the run insert.

EDIT:

Seems like the user want to know how to handle the object creation. I will explain it from the simplest to the safest.

Simplest --> UI level, assume using C# winform:

public void ButtonAddGoods_Click(){
    Goods newGood = new Goods();
    newGood.Id = txtProductId.Text;
    newGood.Description = txtProductDescription.Text;
    newGood.Price = txtProductPrice.Text;

    this.Order.AddNewGood(newGood);
}

The safest (IMHO):

public class GoodBuilder{
    public Goods CreateGood(){
        if(string.IsEmpty(this.Id)) Throw new NullReferenceException("Goods Id is not set");
        //additional validation
        Goods newGood = new Goods();
        newGood.Id = txtProductId.Text;
        newGood.Description = txtProductDescription.Text;
        newGood.Price = txtProductPrice.Text;

        return newGood;
    }
}

public void ButtonAddGoods_Click(){
    GoodBuilder builder = new GoodBuilder();
    builder.Id = this.Id;
    builder.Description = this.Description;
    builder.Price = this.Price;

    this.Order.AddNewGood(builder.CreateGood());
}

edited May 4, 2013 at 7:22

answered May 4, 2013 at 5:21

Fendy

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3 Comments

Samuel Adam Over a year ago

emm so basically I should be using private IEnumerable<Goods> _orderedGoods; and have it's value to be set from property injection? Can you point me somewhere, I'm still confused about how to make user's input in gridview to passable object without instantiating it with the new Object() thing.

Fendy Over a year ago

What I mean is using private List<Goods> _orderedGoods; and has public IEnumerable<Goods> OrderedGoods. Then create a void to Insert the Detail. It will be useful sometimes to when you want to make your object immutable. What are UI you are using? Usually I just accepting the input in native data type (string, etc), do some basic validation and creating the object afterwards.

Samuel Adam Over a year ago

Yes, it's just like what I wanted to know. How to you make the objects from native? Are you passing natives from presentation to business layer for basic validation and then let the business layer make the object?

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