C# 4 and .NET 4

OC304 ❘ ChaPTer 57 windOws wOrkflOw fOundAtiOn 3.0
service can then capture the current state of the workflow and store it in a persistent storage medium. You
could store the workflow state on disk in a file, or store this data within a database such as SQL Server.
The workflow libraries contain an implementation of the persistence service, which stores data within a
SQL Server database — this is the SqlWorkflowPersistenceService. In order to use this service, you
need to run two scripts against your SQL Server instance. One of these constructs the schema, and the other
creates the stored procedures used by the persistence service. These scripts are, by default, located in the
C:\Windows\Microsoft.NET\Framework\v3.5\Windows Workflow Foundation\SQL\EN directory.
The scripts to execute against the database are SqlPersistenceProviderSchema.sql and
SqlPersistenceProviderLogic.sql. These need to be executed in order, with the schema file first and
then the logic file. The schema for the SQL persistence service contains two tables: InstanceState
and CompletedScope. These are essentially opaque tables, and they are not intended for use outside the
SQL persistence service.
When a workflow idles, its state is serialized using binary serialization, and this data is then inserted into
the InstanceState table. When a workflow is reactivated, the state is read from this row and used to
reconstruct the workflow instance. The row is keyed on the workflow instance ID and is deleted from the
database once the workflow has completed.
The SQL persistence service can be used by multiple runtimes at the same time — it implements a locking
mechanism so that a workflow is accessible by only one instance of the workflow runtime at a time. When
you have multiple servers all running workflows using the same persistence store, this locking behavior
becomes invaluable.
To see what is added to the persistence store, construct a new workflow project and add an instance of the
SqlWorkflowPersistenceService to the runtime. The following code shows an example using declarative
code:
using(WorkflowRuntime workflowRuntime = new WorkflowRuntime())
{
workflowRuntime.AddService(
new SqlWorkflowPersistenceService(conn, true, new TimeSpan(1,0,0),
new TimeSpan(0,10,0)));
// Execute a workflow here.
}
If you then construct a workflow that contains a DelayActivity and set the delay to something like
10 seconds, you can then view the data stored within the InstanceState table. The 05 WorkflowPersistence
example contains the preceding code and executes a delay within a 20-second period.
The parameters passed to the constructor of the persistence service are shown in the following table.
ParameTer desCriPTion tefaulT
ConnectionString
UnloadOnIdle
InstanceOwnershipDuration
LoadingInterval
The database connection string used by the
persistence service.
Determines whether a workflow is unloaded when it
idles. This should always be set to true; otherwise no
persistence will occur.
This defines the length of time that the workflow
instance will be owned by the runtime that has loaded
that workflow.
The interval used when polling the database for
updated persistence records.
None
False
None
2 Minutes
These values can also be defined within the configuration file.
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