To dynamically transform one message to another, we need to create mapper object on our own rather then use the Transform shape provided by BizTalk Server.
When we create and deploy a BizTalk Mapper, BTS Engine compiles the created mapper (btm file) into a .Net type, so what we need to do is to obtain the mapper class type and then invoke BizTalk buildin function “transform”to do the transformation.
To obtain mapper type, simply drag an Expression shaep into the orchestration and type the following script in it
var_mapper = Type.GetType(MapperFullQualifiedName);
And in a [Construct Message] shape
transform(outputMessage) = var_mapper(inputMessage)