gistfile1.cs

/// <summary>
/// Adds a model error using strongly typed lambda expressions
/// </summary>
public static void AddModelError<TModel>(
    this ModelStateDictionary modelState, 
    Expression<Func<TModel, object>> method, 
    string message)
{
    if (method == null)
    {
        throw new ArgumentNullException("method");
    }
 
    MemberExpression mce = method.Body as MemberExpression;
	// Handle the case where the property is being converted to typeof(object)
	if (mce == null && method.Body.NodeType == ExpressionType.Convert)
	{
		UnaryExpression ue = (UnaryExpression)method.Body;
		mce = (MemberExpression)ue.Operand;
	}
    string property = mce.Member.Name;
    modelState.AddModelError(property, message);
}