Sep 21 2006

Lazy loading of structures in C# - howto part 8

Posted by admin under In practice

Now, in this part of the "In practice" serie - lets look even deeper into lazy loading.

In our project we have two distinct types - Customer and File - and we do have a clear relation between them. One file is owned by one single customer. One single customer can be associated to many files.

So, our C# class  hierarchy should probably reflect that, don't you think. We have already created classes and collections - so it's easy to add a FileCollection to our customer object:



    public class Customer
    {
        FileCollection m_oFiles = null;
        public FileCollection Files
        {
            get
            {
                if (m_oFiles == null)
                {
                    m_oFiles = new FileCollection();
                    m_oFiles.OpenForCustomer(Id);
                }
                return m_oFiles;
            }
        }

Notice how we lazy load the Files collection - in the beginning it's null - but first time the Property Files is accessed it will be created - and we call OpenForCustomer - sending in the Id for the current customer object.

This makes our old code in editcust.aspx a lot easier to use:

old code:

 



            CustomerClasses.Customer oCustomer = GetCustomer();
            if (oCustomer == null)
            {
                header.InnerText = "New customer";
            }
            else
            {
                header.InnerText = "Edit customer";
                txtName.Text = oCustomer.Custname;

                //Setup repeater existing
                CustomerClasses.FileCollection oColl = new CustomerClasses.FileCollection();
                oColl.OpenForCustomer(oCustomer.Id);
                rptExistingFiles.DataSource = oColl;
                rptExistingFiles.DataBind();

new code:



            CustomerClasses.Customer oCustomer = GetCustomer();
            if (oCustomer == null)
            {
                header.InnerText = "New customer";
            }
            else
            {
                header.InnerText = "Edit customer";
                txtName.Text = oCustomer.Custname;

                //Setup repeater existing
                rptExistingFiles.DataSource = oCustomer.Files;
                rptExistingFiles.DataBind();
            }