Lazy Loading in my C# app

Question

I have a method in my DAL returning a list of Customers:

Collection<Customer> FindAllCustomers();

The Customer has these columns: ID, Name, Address, Bio

I need to show them in a paged grid in my ASPX form (show-customers.aspx) where I'll be showing only these columns: ID, Name

Now, in my DAL FindAllCustomers(), do I return the Bio field too from the SP (I am filling in the collection using a reader)? The Bio field can be large (nvarchar(max)). I was thinking of lazy loading or loading only the required fields. But then in that case I would need to create another method which returns a "full" list of customers including the bio so that 3rd party apps can use it through a service layer. So is it ok to create a method like this:

Collection<Customer> FindAllCustomers(bool loadPartial);

If loadPartial = true, then do not load Bio, else load it. In this case since I do not want to return the Bio from the SP, I would need to create 2 select statements in my SP based on the bool value.

I think using lazy loading here will not work, because then the DAL method can be accessed by a 3rd party app, which might want to load the bio too.

Any suggestions on the best pattern to implement in such cases?

thanks,

Vikas

Answer 1

The 3rd party thing is a bind.

At first blush I would normally suggest that you load only the minimal data normally and then load complete or further detail on an as-requested (i.e. touching a property could trigger a DB call - mild abuse of property there perhaps) or background process basis, depending on the nature of what you're doing.

Lazy property code by way of clarification:

class Customer
{
  private string _lazydata = null;

  public string LazyData
  {
    get
    {
      if (this._lazydata==null)
      {
        LazyPopulate();
      }
      return this._lazydata;
    }
  }

  private void LazyPopulate()
  {
    /* fetch data and set lazy fields */
  }
}

Be careful with this, you don't want to make lots of DB calls but nor do you want to be creating a bottleneck whenever you look at something lazy. Only the nature of your app can decide if this is suitable.

I think you have a valid case for creating the boolean flag method (though I would default to lightweight version) on the grounds that it's very likely a 3rd party would want the lightweight version for the same reasons you do.

I'd go with:

Collection<Customer> FindAllCustomers()
{
  return this.FindAllCustomers(false);
}

Collection<Customer> FindAllCustomers(bool alldata)
{
  /* do work */
}