Dynamic properties and mediation policies

Dynamic properties can be overridden, at run time, using mediation policies.

Introduction

Any property that you promote on a mediation primitive is also a dynamic property, so long as the property is in the top-level request, response, or fault flow. Dynamic properties can be overridden, at run time, using mediation policies in a registry. Although you can override promoted properties dynamically, you must always specify a valid default value.

Promoted properties have a group name, an alias name, a type, and value: all of which you can set from WebSphere® Integration Designer. Multiple promoted properties can be given the same alias name if they are of the same type. You can see the promoted properties on the runtime administrative console, and you can set the property values administratively.

When you use mediation policies, the property group name is used to construct the mediation policy namespace, and the alias name must map to an assertion name in the mediation policy. For example, suppose a property has an alias name of beforeRequestTransform and a group of stockQuoteGroup. The mediation policy refers to the property with the name beforeRequestTransform, and uses the group stockQuoteGroup as the namespace of the mediation policy assertion.

Tip: If mediation primitives occur in subflows, the mediation primitive properties need to be promoted to the top level request, response, or fault flow in order to be modified dynamically.

SMO context

After mediation policy information has been retrieved from the registry, the runtime environment stores it in the dynamicProperty context of the service message object (SMO). The information in the dynamicProperty context can be used to override the values of promoted properties that come later in the flow.

The dynamicProperty context is a system-defined context object; therefore, IBM Integration Designer defines the structure. For every dynamic property, the dynamicProperty context includes the group name, the property name, the property value, and the property type.

Table 1. Elements of the dynamicProperty context
Element	Value	Description
`group`	String	The group name of the property to be overridden.
`name`	String	The alias name of the property to be overridden.
`value`	String	The value to be used.
`type`	String	The property type.

How to override properties

If you want to override a property dynamically you must take the following steps:

From IBM Integration Designer:
1. Promote the property you want to override.
2. Set the elements of the property. Pay particular attention to the group and the alias name.
3. Add a Policy Resolution mediation primitive to your mediation flow. Add it before the mediation primitive whose property you want to override.
4. If you want to retrieve mediation policies for a target service, you should add an Endpoint Lookup primitive to the mediation flow, before the Policy Resolution primitive.
5. Export the EAR file containing your Service Component Architecture (SCA) module.
From WSRR:
1. Load the EAR file containing your SCA module. The registry creates an SCA module document and object, and loads any default mediation policies.
2. If you want to attach mediation policies to target services, rather than to SCA modules, load the WSDL document that represents your target services. The registry creates objects for any service, port, binding, portType, operation, and message elements described by the WSDL; you can attach mediation policies to some of these objects.
  Tip: The runtime environment supports mediation policies attached to service, port, binding, and portType objects. However, the runtime environment does not support mediation policies attached to operation or message objects.
3. If the default mediation policies do not meet your requirements, create a suitable mediation policy.
4. Attach a mediation policy to your SCA module object or to an object associated with your WSDL.
From the administrative console:
1. Import the EAR file containing the SCA module.
2. Ensure that the server is using the correct registry instance.

When available, the mediation policy values take precedence at run time. If a mediation policy is not found, or is unsuitable, the runtime environment uses the promoted property values shown on the administrative console.

If the dynamic override fails for a particular mediation primitive, the fail terminal of that mediation primitive is fired. A dynamic override can fail for a number of reasons. For example, if you try to override the XSL stylesheet of the Mapping mediation primitive, but the stylesheet cannot be found at run time.

How to override properties using a custom mediation

You can override a promoted property without using WSRR by creating a custom mediation. In this example, the "Async timeout" property of a Service Invoke primitive is changed, determined by a value in the input message. The property change applies only to the single invocation of the mediation primitive.

Set up your mediation flow to have your custom mediation wired to a Service Invoke mediation primitive. The custom mediation must be positioned before any primitive being dynamically configured by it in the mediation flow.
In the Service Invoke mediation primitive, navigate to Properties > Promotable Properties. Promote the "Async timeout" property by updating the fields:
1. Select the Promoted check box.
2. Set the alias to ServiceInvoke1.asyncTimeout.
3. Set the group to MyModule.

In the custom mediation, set the property dynamically by selecting Properties > Details and entering the following code sample:

PropertyType property = ServiceMessageObjectFactory.INSTANCE.createPropertyType();
// The alias for the promoted property for the async timeout of the service invoke
property.setName("ServiceInvoke1.asyncTimeout");
// Use the new value for the async timeout (in seconds) from the specified location in the message.
property.setValue(((DataObject)smo).get("/body/operation1/input1/field1"));
DynamicPropertySetType dynamicPropertySet = ServiceMessageObjectFactory.INSTANCE.createDynamicPropertySetType();
// The group of the promoted property
dynamicPropertySet.setGroup("MyModule");
dynamicPropertySet.getProperties().add(property);

DynamicPropertyContextType dynamicPropertyContext = ServiceMessageObjectFactory.INSTANCE.createDynamicPropertyContextType();

dynamicPropertyContext.getPropertySets().add(dynamicPropertySet);

smo.getContext().setDynamicProperty(dynamicPropertyContext);

Tip: All the property values are loaded as Strings. However, an integer must still be entered as a whole number.