Best Practices for context management in Windows Forms

RELATED TO:

Article information

Article relates to

 Telerik OpenAccess ORM

Created by

 Zoran Kostov

Last modified

 April 26, 2010

Last modified by

 Serge Ovanesyan

The context is quite easy to handle in a desktop application. One of the most elegant and generic ways to do so is managing one scope per thread by storing it in a thread-specific LocalDataStoreSlot.

Here is a sample ContextFactory class that contains one static method for scope-retrieval:

public class ContextFactory
{
    public static NorthwindEntityDiagrams ObtainContext()
    {
        NorthwindEntityDiagrams context = null;
 
        string key = Thread.CurrentContext.ContextID.ToString();
         
        LocalDataStoreSlot slot = Thread.GetNamedDataSlot(key);
        if(slot != null)
        {
            context = (NorthwindEntityDiagrams) Thread.GetData(slot);
        }
        if(context == null)
        {
            context = new NorthwindEntityDiagrams();
            if(slot == null)
            {
                slot = Thread.AllocateNamedDataSlot(key);
            }
            Thread.SetData(slot, context);
        }
        return context;
 
    }
}

By obtaining the context using this approach all the various forms and user controls in a desktop application can communicate using the same context instance given they are created on the same thread. That may seem suspicious for a multi-threaded scenario but it actually is not a very common case that controls created on different threads share the same business object.


Sample scenario:

We have a windows form with two user controls on it. The user controls are quite simple ones: the first contains one RadComboBox on it and the other a RadGridView. In the code-behind of both user-controls they have sample data-binding logic:

public partial class ComboBoxUserControl : UserControl
{
    ...
 
    private void ComboBoxUserControl_Load(object sender, EventArgs e)
    {
        var context = ContextFactory.ObtainContext();
        IList<Customer> results = context.Customers.ToList();
        this.radComboBox1.DataSource = results;
        this.radComboBox1.DisplayMember = "ContactName";
        this.radComboBox1.ValueMember = "CustomerID";
    }
}

public partial class GridUserControl : UserControl
{
    ...
 
    private void GridUserControl_Load(object sender, EventArgs e)
    {
        NorthwindEntityDiagrams ctx = ContextFactory.ObtainContext();
        IList<Order> results = ctx.Orders.ToList();
        radGridView1.DataSource = results;
    }
}

The main form where both user controls are dropped has some own business logic. So it reuses the same Context instance.

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
        this.comboBoxUserControl1.Combo.SelectedIndexChanged += new EventHandler(Combo_SelectedIndexChanged);
    }
 
    void Combo_SelectedIndexChanged(object sender, EventArgs e)
    {
        RadComboBox combo = ((RadComboBox)sender);
        if (combo.SelectedValue != null)
        {
            string customerId = combo.SelectedValue.ToString();
            NorthwindEntityDiagrams context = ContextFactory.ObtainContext();
            IList<Order> results = context.Orders.Where(x => x.CustomerID == customerId).ToList();
            this.gridUserControl1.Grid.DataSource = results;
        }
    }
}

The full code from the sample is available in Telerik OpenAccess ORM code-library.

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