Query Table Index by Expression Sample

Introduction

This sample consists of a simple EventFlow application, QueryIndexByExpression.sbapp, that illustrates the Query Table's index by expression feature. This feature allows you to use an expression as part of specifying the field or fields that comprise a secondary index for a Query Table. The expression must be statically resolvable, and must contain the name of at least one field in the Query Table's schema.

This sample's Query Table has the schema {string symbol, double lastPriceChange} and is automatically populated with the following values by means of the Initial Contents tab of the table's Properties view:

IBM, -4.3

MSFT, 6.7

GOOG, -2.3

APPL, 9.3

The field name portion of the Query Table's secondary index is specified with the expression abs(lastPriceChange). This simple expression allows you to enter either a query value either as a positive or negative number and obtain the same result. For example, if a Query operator specifies a Read operation based on this secondary index, you could enter either 4.3 or –4.3 to obtain the result IBM.

Running This Sample in StreamBase Studio

In the Package Explorer, double-click to open the QueryIndexByExpression.sbapp application. Make sure the application is the currently active tab in the EventFlow Editor.
Click the Run button. This opens the SB Test/Debug perspective and starts the application.
In the Manual Input view, the QueryByPriceDelta input stream is preselected. Enter one of the values from the initially loaded contents shown above, as either a positive or negative number. For example, enter –4.3, then enter 4.3.
Click Send Data, and a tuple arrives in the Application Output view. In both cases, the Application Output view shows the IBM row of the Query Table returned on the QueryResults stream.
Continue experimenting with values from the list above, or values not in the list.
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 the directory where the sample is installed, or to your workspace copy of the sample, as described above.
In window 1, type: sbd QueryIndexByExpression.sbapp
In window 2, type: sbc deq QueryResults

No output is displayed at this point, but the dequeuer is prepared to receive output. This window will eventually show the output of the application.
In window 3, type: sbc enq queryPriceChange

The sbc command in window 3 now waits for keyboard input. Type:

4.3

Observe this table row emitted in window 2:

IBM,-4.3
In window 3, type:

-4.3

Observe the same table row emitted in window 2:

IBM,-4.3
Continue typing values in window 2.
When done, in window 3, type: Ctrl+C to exit the enqueue session.
In window 3, type the following command to terminate the server and dequeuer:

sbadmin shutdown

Importing This Sample into StreamBase Studio

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

From the top menu, click File → Load StreamBase Sample.
In the search field, type oper to narrow the list of samples.
From the Data Constructs and Operators category, select Operator Sample Group.
Click OK.

StreamBase Studio creates a single project for the operator sample group.

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

Load this sample in StreamBase Studio, and thereafter use the Studio 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 can occur when trying to work with the initially installed location of the sample. The default workspace location for this sample is:

studio-workspace/sample_operator

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

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

streambase-install-dir/sample/operator

See Default Installation Directories for the location of streambase-install-dir on your system. This location may require administrator privileges for write access, depending on your platform.

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