Question

I need some advice on modeling an ecommerce domain.

The client sells two products:

1. Custom art work, the design specified by the customer.
2. Prints of art with a message on the back specified by the customer.

Here is my cut down database model so far.

Products:
    Id
    Description
    Price

Orderlines:
    Id
    OrderId
    ProductId

Attributes:
    Id
    Name

OrderAttributes:
    AttributeId
    OrderlineId
    Value

The products table will have the 2 products from above.

The order line links the selected product to an order.

The attributes holds the custom field names for each product.

For example the custom artwork product would have the attribute design.

The order attributes links the ordered product to it’s customs attributes and has the value.
For example custom artwork product, with an attribute of design, with a value of paint a house.

I would also like to map this database model to code as well using nhibernate.

Is there a better way of modeling this data?

Answer 1

A couple of suggestions:

The Orderlines table should contain the price (and possibly the description) of the product so that item prices can change without affecting existing orders. Similarly, the Orders table (not shown) should contain customer information (e.g. shipping address) that may change. The data that makes up an order can’t change and the easiest approach is to flatten and denormalize it.

The OrderAttributes structure is called an entity-attribute-value model and it has many drawbacks. In general I recommend avoiding it and adding the needed columns to the Orderlines table. If needed, your application can subclass Product and OrderLine so that a CustomArtWorkProduct creates a CustomArtWorkOrderLine when it’s added to an order.