dataset question

[dinger2121]

Hello,
I added a dataset class to my project in order to create a strongly typed dataset. I am getting a null value error and realize that I have to change the NullValue property of column to something other than (Throw Exception).

My question is whether I should set it to (Null) or (Empty).

Thanks for any thoughts.

carl
MCSD, MCTS:MOSS

 

[jmeckley]

i didn't think datasets allows null values. but it's been a long time since I worked with them.

also what is the data type. Empty makes me think of string, not int or Datetime. if that's the case then choosing null or empty is a choice you need to make as null is nothing and empty is a blank value. if your system interprets a null differently than an empty string you need to consider that when configuring the dataset.

if you system doesn't distinguish between null and empty string then I would use an empty string. you can still preform operations on an empty string where as a null string you need to check for null before using the string. this is an example of the Null Object pattern.

Jason Meckley
Programmer
Specialty Bakers, Inc.

faq855-7190

 

[dinger2121]

That is what I had been thinking. they are string datatypes, and the properties allow both, so I think I will stick with the empty string.

Thanks

carl
MCSD, MCTS:MOSS

 

[jmeckley]

why mess with datasets at all? why not use POCOs to explicitly define the domain?

Jason Meckley
Programmer
Specialty Bakers, Inc.

faq855-7190

 

[dinger2121]

I am not familiar with POCO - I will look into it.

Thanks

carl
MCSD, MCTS:MOSS

 

[jmeckley]

POCO = plain old compiled/c# object. the most common example is Customer > Order > OrderLines model. here is just one way to implement that.

class Customer
{
   public long Id {get; private set;}
   public string Name  {get; set;}
   public Address ShippingAddress {get; private set;}

   public void SetId(long id)
   {
      Id = id;
   }

   public void Change(Address shippingAddress)
   {
       ShippingAddress = shippingAddress;
   }
}

class Order
{
    private IList<OrderLine> lines;
    public Order(Customer customer)
    {
       Customer = customer;
       lines = new List<OrderLine>();
    }

    public long OrderNumber {get;set;}
    public Customer Customer {get; private set;}
    public DateTime OrderPlacedOn {get;set;}
    public IEnumerable<OrderLine> Lines {get {return lines; }}

    public void Add(Product product, int quantity)
    {
        if(!lines.Any(l=>l.Product == Product)
        {
           lines.Add(new OrderLine(this, Product);
        }
        lines.First(l=>l.Product == Product).IncrementQuantityBy(quantity);
    }

public void Remove(Product product)
    {
        if(!lines.Any(l=>l.Product == Product) return;
        var line = lines.First(l=>l.Product == Product);
        lines.Remove(line);
    }
}

class OrderLine
{
    public OrderLine(Order order, Product product)
    {
       Order = order;
       Product = product;
    }

    public Order Order {get; private set;}
    public Product Product {get; private set;}
    public int Quantity {get; private set;}

    public void IncrementQuantityBy(int amount)
    {
         Quantity += amount;
    }
}

this creates a very explicity model, encapsulates logic within the entities themselves, and removes all the overhead of DataSet/DataTable operations.

frameworks like Nhibernate and ActiveRecord make it easy to map these objects to a database for persistence.

Jason Meckley
Programmer
Specialty Bakers, Inc.

faq855-7190