/// <summary>
/// Constructs the event filter for the subscription.
/// </summary>
/// <returns>The event filter.</returns>
public EventFilter ConstructFilter(Session session)
{
EventFilter filter = new EventFilter();
// the select clauses specify the values returned with each event notification.
filter.SelectClauses = SelectClauses;
// the where clause restricts the events returned by the server.
// it works a lot like the WHERE clause in a SQL statement and supports
// arbitrary expession trees where the operands are literals or event fields.
ContentFilter whereClause = new ContentFilter();
// the code below constructs a filter that looks like this:
// (Severity >= X OR LastSeverity >= X) AND (SuppressedOrShelved == False) AND (OfType(A) OR OfType(B))
// add the severity.
ContentFilterElement element1 = null;
ContentFilterElement element2 = null;
if (Severity > EventSeverity.Min)
{
// select the Severity property of the event.
SimpleAttributeOperand operand1 = new SimpleAttributeOperand();
operand1.TypeDefinitionId = ObjectTypeIds.BaseEventType;
operand1.BrowsePath.Add(BrowseNames.Severity);
operand1.AttributeId = Attributes.Value;
// specify the value to compare the Severity property with.
LiteralOperand operand2 = new LiteralOperand();
operand2.Value = new Variant((ushort)Severity);
// specify that the Severity property must be GreaterThanOrEqual the value specified.
element1 = whereClause.Push(FilterOperator.GreaterThanOrEqual, operand1, operand2);
}
// add the suppressed or shelved.
if (!IgnoreSuppressedOrShelved)
{
// select the SuppressedOrShelved property of the event.
SimpleAttributeOperand operand1 = new SimpleAttributeOperand();
operand1.TypeDefinitionId = ObjectTypeIds.BaseEventType;
operand1.BrowsePath.Add(BrowseNames.SuppressedOrShelved);
operand1.AttributeId = Attributes.Value;
// specify the value to compare the Severity property with.
LiteralOperand operand2 = new LiteralOperand();
operand2.Value = new Variant(false);
// specify that the Severity property must Equal the value specified.
element2 = whereClause.Push(FilterOperator.Equals, operand1, operand2);
// chain multiple elements together with an AND clause.
if (element1 != null)
{
element1 = whereClause.Push(FilterOperator.And, element1, element2);
}
else
{
element1 = element2;
}
}
// add the event types.
if (EventTypes != null && EventTypes.Count > 0)
{
element2 = null;
// save the last element.
for (int ii = 0; ii < EventTypes.Count; ii++)
{
// for this example uses the 'OfType' operator to limit events to thoses with specified event type.
LiteralOperand operand1 = new LiteralOperand();
operand1.Value = new Variant(EventTypes[ii]);
ContentFilterElement element3 = whereClause.Push(FilterOperator.OfType, operand1);
// need to chain multiple types together with an OR clause.
if (element2 != null)
{
element2 = whereClause.Push(FilterOperator.Or, element2, element3);
}
else
{
element2 = element3;
}
}
// need to link the set of event types with the previous filters.
if (element1 != null)
{
whereClause.Push(FilterOperator.And, element1, element2);
}
}
filter.WhereClause = whereClause;
// return filter.
return filter;
}
/// <summary>
/// Returns the subscription filter to use.
/// </summary>
public EventFilter GetFilter()
{
ContentFilter whereClause = new ContentFilter();
ContentFilterElement element1 = whereClause.Push(FilterOperator.OfType, EventTypeId);
EventFilter filter = new EventFilter();
for (int ii = 0; ii < Fields.Count; ii++)
{
filter.SelectClauses.Add(Fields[ii].Operand);
if (Fields[ii].FilterValue != Variant.Null)
{
LiteralOperand operand = new LiteralOperand();
operand.Value = Fields[ii].FilterValue;
ContentFilterElement element2 = whereClause.Push(Fields[ii].FilterOperator, Fields[ii].Operand, operand);
element1 = whereClause.Push(FilterOperator.And, element1, element2);
}
}
filter.WhereClause = whereClause;
return filter;
}
