Capture Fields for Generic Data Store Sample

Introduction

This sample demonstrates how to use a capture field in the schema of a Query Table to make that table reusable in different copies of its containing module. Each instance of the table holds key-value data with different value data types for different instances.

The schema for a Query Table that holds key-value pairs would normally have two fields, a key field and a data field of a particular data type. The schema for such a table might be, for example, {key long, data string}. Before capture fields, to store a key-value pair of with a different data type, you would need a separate Query Table with a different schema, such as {key long, data double}.

The Query Table in this sample instead uses a capture field for the data field. Capture fields are only active in the context of a module, so the Query Table, GenericDataStore, is placed in the module GenericDataStore.sbapp. Notice that its schema is {id long, data capture}. This capture field's field name is data, while its defined data type is dataFields. This schema means: expect the first field to be named id and to have data type long; then expect any number of fields with different types thereafter.

The inner module is completed with a Query operator to insert values and another to report the count of rows accumulated in the table so far.

The inner module, GenericDataStore.sbapp is referenced twice in the outer module, TopLevel.sbapp. In the first reference, an input stream, Points, with schema {id long, x int, y int} feeds into the inner module's DataIn stream. The first field, id, matches the Query Table's requirement for a first field of type long named id. The x and y fields are captured by the Query Table's capture field, which adapts the first instance of the GenericDataStore Query Table to have the same schema as the Points input stream.

In the second reference, the input stream, Names, with schema {id long, name string} feeds into another instance of the inner module's DataIn stream. In this case, the Query Table in the second instance of the inner module adapts its schema to match the Names input stream.

Reusing the inner module does not mean there is a single Query Table that changes its schema. It means there are two instances of the Query Table, one per module reference, with different schemas that match the two input streams. Notice that the same abstract Query Table schema definition is used without change in both module references, yet each instance of the Query Table ends up with different concrete schemas at runtime.

A simple feed simulation is provided that feeds generated values to all four input streams as follows:

Input Stream	Feed Simulation Action
Names	100 tuples of generated `id`, `string` value pairs at 10 tuples per second.
Points	50 tuples of generated `id`, `x`, `y` values at 10 tuples per second.
CountNamesRows	One no-fields tuple every second, which triggers a count of all rows in the Names instance of the Query Table.
CountPointsRows	One no-fields tuple every second, which triggers a count of all rows in the Points instance of the Query Table.

The result of running the feed simulation is that the two instances of the inner module's Query Table are populated with generated values, each of the appropriate data type. Meanwhile, once per second, Studio's Application Output view reports the number of rows accumulated so far in each of the two tables.

Running This Sample in StreamBase Studio

In the Package Explorer, double-click to open the TopLevel.sbapp module. Make sure the module is the currently active tab in the EventFlow Editor.
Click the Run button. This opens the SB Test/Debug perspective and starts the module.
Select the Feed Simulations view, select the TopLevel.sbfs feed simulation, and click Run.
View the results in the Application Output view.
You can rerun the feed simulation to continue adding values to the sample's Query Table.
When done, press F9 or click the Stop Running Application button.

Running This Sample in Terminal Windows

This section describes how to run the sample in UNIX terminal windows or Windows command prompt windows. On Windows, be sure to use the StreamBase Command Prompt from the Start menu as described in the Test/Debug Guide, not the default command prompt.

Open three terminal windows on UNIX, or three StreamBase Command Prompts on Windows. In each window, navigate to your workspace copy of the sample, as described below.
In window 1, launch StreamBase Server running TopLevel.sbapp:

sbd TopLevel.sbapp
In window 2, run a dequeuer for the two output streams:

sbc deq PointsTable NamesTable

(You can optionally run separate dequeuers in separate windows.)
In window 3, run the feed simulation:

sbfeedsim TopLevel.sbfs
In window 2, watch the row count accumulate separately for the two Query Tables.
To stop the sample, run sbadmin shutdown.

Note

Unlike the feed simulator in Studio, by default, the sbfeedsim command resets its random number generator with the same initial seed for each invocation. This means that if you rerun the sbfeedsim command above, the application returns the same values. To continue adding random values to this sample's Query Table, use the -z option with its clock argument, which seeds the random number generator from the now() timestamp:

sbfeedsim -z clock TopLevel.sbfs

Importing This Sample into StreamBase Studio

In StreamBase Studio, import this sample with the following steps:

From the top menu, select File → Load StreamBase Sample.
In the search field, type capture to narrow the list of samples.
Select CaptureGenericDataStore from the Data Constructs and Operators category.
Click OK.

StreamBase Studio creates a single project containing the sample files.

Sample Location

When you load the sample into StreamBase Studio, Studio copies the sample project's files to your Studio workspace, which is normally part of your home directory, with full access rights.

Important

StreamBase Systems strongly recommends that you load this sample in Studio, and use the workspace copy of the sample to run and test it, even when running from the command prompt.

Using the workspace copy of the sample avoids the permission problems that are inevitable when trying to work with the installed location in C:\Program Files or /opt/streambase. The default workspace location for this sample is:

studio-workspace/sample_CaptureGenericDataStore

See Default Installation Directories for the location of studio-workspace on your system.

In the default StreamBase installation, this sample's files are installed in:

streambase-install-dir/sample/CaptureGenericDataStore

See Default Installation Directories for the location of streambase-install-dir on your system. This location usually requires administrator privileges for write access.