Question

Given that every grid, combobox, checkboxlist and in general multi row control supports binding directly to any IEnumerable what is the point of the ObjectDataSource?

Why would one use it as opposed to binding directly to your collection? Particularly if you already have reasonable separation of concerns in your business, presentation and data layers?

I also feel this is an even more relevant question since the introduction of LINQ. I have often found that when binding I would like to perform some further ordering, exclusion and so forth using LINQ and I believe this is not possible when using the ObjectDataSource without creating a specific method for your (potentially single use case)?

So when is it appropriate to use an ObjectDataSource and what are the advantages compared to direct binding to IEnumerable?

Answer 1

First, ObjectDataSource is usually used in ASP.NET WebForms (aspx). ObjectDataSource is located in System.Web.UI.WebControls, as you can see this link on MSDN Library:

http://msdn.microsoft.com/en-us/library/system.web.ui.webcontrols.objectdatasource.aspx

Using ObjectDataSource to bind your data means you bind you’ll have datasource as an object, can be in form of DataSet or any other .NET object that implements IEnumerable. Using ObjectDataSource means you have to perform your own Select, Update, Insert and Delete method that usually found in SqlDataSource.

There’s this nice walkthrough in MSDN Library: Walkthrough: Data Binding to a Custom Business Object

But binding to a simple IEnumerable without implementing IListSource (like DataTable has) means you won’t have nice feature such as data bindings to a complex data control such as GridView. And you’ll lose other feature too, because a simple IEnumerable alone can’t be bound in two ways to other list control such as ListView and GridView.

To have your data to be bindable two way, your object must also implement INotifyPropertyChanged interface before added into the IListSource as data item.

Samples:

public class Employee : BusinessObjectBase
{
    private string      _id;
    private string      _name;
    private Decimal     parkingId;

    public Employee() : this(string.Empty, 0) {}
    public Employee(string name) : this(name, 0) {}

    public Employee(string name, Decimal parkingId) : base()
    {
        this._id = System.Guid.NewGuid().ToString();

        // Set values
        this.Name = name;
        this.ParkingID = parkingId;
    }

    public string ID
    {
        get { return _id; }
    }

    const string NAME = "Name";
    public string Name
    {
        get { return _name; }
        set
        {
            if (_name != value)
            {
                _name = value;

                // Raise the PropertyChanged event.
                OnPropertyChanged(NAME);
            }
        }
    }

    const string PARKING_ID = "Salary";
    public Decimal ParkingID
    {
        get { return parkingId; }
        set
        {
            if (parkingId != value)
            {
                parkingId = value;

                // Raise the PropertyChanged event.
                OnPropertyChanged(PARKING_ID);
            }
        }
    }
}

This is the implementation of INotifyPropertyChanged:

public class BusinessObjectBase : INotifyPropertyChanged
{
    #region INotifyPropertyChanged Members

    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged(string propertyName)
    {
        OnPropertyChanged(new PropertyChangedEventArgs(propertyName));
    }

    private void OnPropertyChanged(PropertyChangedEventArgs e)
    {
        if (null != PropertyChanged)
        {
            PropertyChanged(this, e);
        }
    }

    #endregion
}