Inside the StreamInsight Object Model – Metadata

The StreamInsight object model seems fairly complex at first. There's a series of choices as you progress down the development path which make things appear more complex than they are. One thing to keep in mind is, no matter how you populate it, there is only one object model that encapsulates the metadata.

One way to get a handle of the model is to look into the metadata. The easiest way to do this is to use SQL Server CE to register your metadata. If you don't specify SQL Server CE at runtime, the default behavior is to store the information in memory, making it more difficult to see.

Note that the included standalone server host application, StreamInsight.exe, can use either SQL Server CE or inprocess metadata based on the presence of a configuration file setting.

To use SQL Server CE, use the Explicit Server Development Model (StreamInsight Books Online has nice information comparing and contrasting the development models), but instead of using:

Server s = Server.Create();

these additional lines will use SQL Server CE.

SqlCeMetadataProviderConfiguration config = new SqlCeMetadataProviderConfiguration();
config.DataSource = "MyMetabase.sdf";  // these should be in a config file
config.CreateDataSourceIfMissing = true;
Server s = Server.Create(config);

When you register the rest of the StreamInsight objects (Application, EventTypes, Adapters, etc), the metadata will be written into the CE database. Because the database information does not disappear when the application completes (unless you specifically delete it), you can browse the StreamInsight metadata afterwards.

You can also go a step further than that. Because the metadata is stored in the database, its possible to pre-provision the database with the registration information by running the program once. With a pre-provisioned database your program would consist of creating the Server (as in the code above) and pulling out the configuration like this:

Application a = s.Applications["TheApplication"]; // the Application name from original run
if (a == null)
  throw new Exception("Application Metadata Not Found");

It's possible to run your entire application this way, because all of the metadata you provided has been stored with full fidelity in the CE database. If you run, say, the sample ExplicitServer app this way, you need only fetch the Application and Query objects and start your Query. The other objects (Adapters, EventTypes, Bindings, Streams, and QueryTemplate) are already in place from the database where you populated the metadata originally.

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