C# 4 and .NET 4

1330 ❘ ChaPTer 44 windOws wOrkflOw fOundAtiOn 4
return new Sequence
{
Variables = { propertyId, operationHandle, finished,
address, owner, askingPrice },
Activities =
{
receive,
new WriteLine { Text = "Assigning a unique ID" },
new Assign
{
To = new OutArgument (propertyId),
Value = new InArgument (Guid.NewGuid())
},
new SendReply
{
Request = receive,
Content = SendContent.Create
(new InArgument (env => propertyId.Get(env))),
CorrelationInitializers =
{
new QueryCorrelationInitializer
{
CorrelationHandle = operationHandle,
MessageQuerySet = extractGuid
}
}
}
// Other activities omitted for clarity
}
};
Next, the SendReply activity is used to respond to the caller with the Guid defined by the workflow. This
part is fairly complex.
The SendReply activity is linked to the initial Receive activity by setting its Request property to the
receive activity instance. The return value of the operation is defined by the Content property. There are
three types of responses that can be returned from an operation — a discrete value, such as a Guid used
here, a set of parameters defined by a dictionary of name/value pairs, or a message type. The SendContent
class is a helper that constructs the appropriate object for you.
The last part is the most complex. The CorrelationInitializers property is effectively used to extract
a correlation token from the current message and use this in subsequent calls to the workflow to uniquely
identify the workflow. The MessageQuerySet is used to do the extraction and is defined as shown below for
this outgoing message. Once the query has been defined, it is then linked with a handle value. This handle is
used by any other activity wishing to be part of the same correlation group.
MessageQuerySet extractGuid = new MessageQuerySet
{
{ "PropertyId",
new XPathMessageQuery ( "sm:body()/ser:guid", messageContext ) }
};
This query uses XPath (otherwise known as voodoo magic) to extract data from the message being sent
back to the client. Here, it is reading the body element and, within that, looking for the value of the guid
element within the message.
awaiting events with Pick
So, we’ve constructed a new workflow instance and replied to the caller with a unique operation ID. The
next part is to await further data from the client, which is done with two further Receive activities.
The first of these corresponds to the UploadRoomInformation operation.
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