Creating the business logic layer

Now let's create the business logic layer. The steps here are very similar to the steps in Chapter 4, Implementing a WCF Service in the Real World, so you can refer to that chapter for more details.

  1. Right click on the solution item and select Add | New Project.... Add a class library project with the name LINQNorthwindLogic.
  2. Add a project reference to LINQNorthwindDAL and LINQNorthwindBDO to this new project.
  3. Delete the Class1.cs file.
  4. Add a new class file ProductLogic.cs.
  5. Change the new class ProductLogic to be public.
  6. Add the following two using statements to the ProductLogic.cs class file:
    using LINQNorthwindDAL;
using LINQNorthwindBDO;
  7. Add the following class member variable to the ProductLogic class:
    ProductDAO productDAO = new ProductDAO();
  8. Add the following new method GetProduct to the ProductLogic class:
    public ProductBDO GetProduct(int id)
{
    return productDAO.GetProduct(id);
}
  9. Add the following new method UpdateProduct to the ProductLogic class:
    public bool UpdateProduct(
  ref ProductBDO productBDO, 
  ref string message)
{
    var productInDB =
        GetProduct(productBDO.ProductID);
    // invalid product to update
    if (productInDB == null)
    {
        message = "cannot get product for this ID";
        return false;
    }
    // a product cannot be discontinued 
    // if there are non-fulfilled orders
    if (productBDO.Discontinued == true
        && productInDB.UnitsOnOrder > 0)
    {
        message = "cannot discontinue this product";
        return false;
    }
    else
    {
        return productDAO.UpdateProduct(ref productBDO,
            ref message);
    }
}

Build the solution. We now have only one more step to go, that is, adding the service interface layer.

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