Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>Consider a simple shopping cart application that uses a CartContents class to keep track of the items in the shopping cart and an Order class for processing a purchase. The Order needs to determine the total value of the contents in the cart, it might do that like so:</p> <p><strong>Tightly Coupled Example:</strong></p> <pre class="lang-cs prettyprint-override"><code>public class CartEntry { public float Price; public int Quantity; } public class CartContents { public CartEntry[] items; } public class Order { private CartContents cart; private float salesTax; public Order(CartContents cart, float salesTax) { this.cart = cart; this.salesTax = salesTax; } public float OrderTotal() { float cartTotal = 0; for (int i = 0; i &lt; cart.items.Length; i++) { cartTotal += cart.items[i].Price * cart.items[i].Quantity; } cartTotal += cartTotal*salesTax; return cartTotal; } } </code></pre> <p>Notice how the OrderTotal method (and thus the Order class) depends on the implementation details of the CartContents and the CartEntry classes. If we were to try to change this logic to allow for discounts, we'd likely have to change all 3 classes. Also, if we change to using a List collection to keep track of the items we'd have to change the Order class as well.</p> <p>Now here's a slightly better way to do the same thing:</p> <p><strong>Less Coupled Example:</strong></p> <pre class="lang-cs prettyprint-override"><code>public class CartEntry { public float Price; public int Quantity; public float GetLineItemTotal() { return Price * Quantity; } } public class CartContents { public CartEntry[] items; public float GetCartItemsTotal() { float cartTotal = 0; foreach (CartEntry item in items) { cartTotal += item.GetLineItemTotal(); } return cartTotal; } } public class Order { private CartContents cart; private float salesTax; public Order(CartContents cart, float salesTax) { this.cart = cart; this.salesTax = salesTax; } public float OrderTotal() { return cart.GetCartItemsTotal() * (1.0f + salesTax); } } </code></pre> <p>The logic that is specific to the implementation of the cart line item or the cart collection or the order is restricted to just that class. So we could change the implementation of any of these classes without having to change the other classes. We could take this decoupling yet further by improving the design, introducing interfaces, etc, but I think you see the point.</p>
    singulars
    1. This table or related slice is empty.
    1. POWhat is "loose coupling?" Please provide examples
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USFrancois Bourgeois
    1. USWedge
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. COCould you expand the answer introducing further decoupling through dependency injection (though constructor should be ideal)?
      singulars
      1. PO
      1. USBAD_SEED
    2. CO@Wedge, I see no reason for the `Order` to have any knowledge of a `Cart`. Live shopping and facturation are two different contexts. When the client is ready to pay, you could have a process responsible to translate CartEntries into something meaninful for the `Order`. This way the `Order` class would also be instanciated and used without a `Cart`.
      singulars
      1. PO
      1. USplalx
    3. CO@Wedge Could you react to my comment please?
      singulars
      1. PO
      1. USplalx
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload