WebSphere Message Brokers
File: ac04670_
Writer: Terry Cowling

Reference topic

This build: July 31, 2007 21:17:31

Database node

This topic describes the Database node.

Purpose

Use the Database node to interact with a database in the specified ODBC data source. You define the nature of the interaction by coding ESQL statements that specify the data from the input message, and perhaps transform it in some way (for example, to perform a calculation), and assign the result to a database table.

You can set a property to control whether the update to the database is committed immediately, or deferred until the message flow completes, at which time the update is committed or rolled back, according to the overall completion status of the message flow.

Although you can use this node to update the database, you cannot make any updates to the message.

You can use specialized forms of this node to:
  • Update values within a database table (the DataUpdate node)
  • Insert rows into a database table (the DataInsert node)
  • Delete rows from a database table (the DataDelete node)
  • Store the message, or parts of the message, in a warehouse (the Warehouse node)

The Database node is contained in the Database drawer of the palette, and is represented in the workbench by the following icon:

Database node icon

Using this node in a message flow

Look at the following samples to see how to use this node: You can view samples only when you use the information center that is integrated with the Message Brokers Toolkit.

Consider a situation in which you receive an order for 20 monitors. If you have sufficient numbers of monitors in your warehouse, you want to decrement the stock level on your stock database. You can use the Database node to check that you have sufficient monitors available, and decrement the value of the quantity field in your database.

Configuring the Database node

When you have put an instance of the Database node into a message flow, you can configure it; see Configuring a message flow node. The properties of the node are displayed in the Properties view.

All mandatory properties for which you must enter a value (those that do not have a default value defined) are marked with an asterisk.

Configure the Database node as follows:

  1. Optional: On the Description tab, enter a short description, a long description, or both. You can also change the name of the node on this tab.
  2. On the Basic tab:
    1. Specify in Data Source the name by which the appropriate database is known on the system on which this message flow is to execute. The broker connects to this database with user ID and password information that you have specified on the mqsicreatebroker, mqsichangebroker, or mqsisetdbparms command.

      z/OS platform On z/OS systems, the broker uses the broker started task ID, or the user ID and password that were specified on the mqsisetdbparms command JCL, BIPSDBP in the customization data set <hlq>.SBIPPROC.

    2. In Statement, identify the module within an ESQL file that contains the ESQL statements that are to be executed in this node. If you want the module name to include one or more spaces, enclose the name in double quotes in the Statement property.

      The ESQL file, which by default has the name <message_flow_name>.esql, contains ESQL for every node in the message flow that requires it. Each portion of code that is related to a specific node is known as a module.

      When you code ESQL statements that interact with tables, those tables are assumed to exist within this database. If they do not exist, a database error is generated by the broker at run time.

      Code ESQL statements to customize the behavior of the Database node in an ESQL file that is associated with the message flow in which you have included this instance of the Database node.

      If an ESQL file does not exist already for this message flow, double-click the Database node, or right-click the node and click Open ESQL to create and open a new ESQL file in the ESQL editor view.

      If an ESQL file exists already, click Browse beside the Statement property to display the Module Selection dialog box, which lists the available Database node modules that are defined in the ESQL files that are accessible by this message flow (ESQL files can be defined in other, dependent, projects). Select the appropriate module and click OK. If no suitable modules are available, the list is empty.

      If the module that you have specified does not exist, it is created for you and the editor displays it. If the file and the module exist already, the editor highlights the correct module.

      If a module skeleton is created for this node in a new or existing ESQL file, it consists of the following ESQL. The default module name is shown in this example:

      CREATE DATABASE MODULE <flow_name>_Database
             CREATE FUNCTION Main() RETURNS BOOLEAN
             BEGIN
                     RETURN TRUE; 
             END;
      END MODULE;

      If you create your own ESQL module, create exactly this skeleton. You can update the default name, but ensure that the name that you specify matches the name of the corresponding node property Statement.

      To customize this node, add your own ESQL after the BEGIN statement and before RETURN TRUE.

      You can use all the ESQL statements including SET, WHILE, DECLARE, and IF in this module, but (unlike the Compute node) the Database node propagates, unchanged, the message that it receives at its input terminal to its output terminal. Therefore, like the Filter node, you have only one message to refer to in a Database node.

      You cannot modify any part of any message, so the assignment statement (the SET statement, not the SET clause of the INSERT statement) can assign values only to temporary variables. The scope of actions that you can take with an assignment statement is therefore limited.

    3. Select the Transaction setting from the drop-down menu. The values are:
      • Automatic (the default). The message flow, of which the Database node is a part, is committed if it is successful; that is, the actions that you define in the ESQL module are performed and the message continues through the message flow. If the message flow fails, it is rolled back. If you select Automatic, the ability to commit or roll back the action of the Database node on the database depends on the success or failure of the entire message flow.
      • Commit. To commit any uncommitted actions that are performed in this message flow on the database that is connected to this node, irrespective of the success or failure of the message flow as a whole, select Commit. The changes to the database are committed even if the message flow itself fails.
    4. For database warning messages to be treated as errors, and the node to propagate the output message to the Failure terminal, select Treat Warnings as Errors. The check box is cleared initially.

      When you select the check box, the node handles all positive return codes from the database as errors and generates exceptions in the same way as it does for the negative, or more serious, errors.

      If you do not select the check box, the node treats warnings as normal return codes, and does not raise any exceptions. The most significant warning raised is not found, which can be handled as a normal return code safely in most circumstances.

    5. For the broker to generate an exception when a database error is detected, select Throw Exception on Database Error. The check box is selected initially.

      If you clear the check box, include ESQL to check for any database error that might be returned after each database call that you make (you can use SQLCODE and SQLSTATE to do this). If an error has occurred, you must handle the error in the message flow to ensure the integrity of the broker and the database; the error is ignored if you do not handle it through your own processing because you have chosen not to invoke the default error handling by the broker. For example, you can include the ESQL THROW statement to throw an exception in this node, or you can use the Throw node to generate your own exception at a later point.

Terminals and properties

The terminals of the Database node are described in the following table.

Terminal Description
In The input terminal that accepts a message for processing by the node.
Failure The output terminal to which the input message is propagated if a failure is detected during the computation. If you have selected Treat warnings as errors, the node propagates the message to this terminal even if the processing completes successfully.
Out The output terminal to which the transformed message is routed when processing in the node is completed. The transformed message might also be routed to this terminal by a PROPAGATE statement.
Out1 The first alternative output terminal to which the transformed message might be routed by a PROPAGATE statement.
Out2 The second alternative output terminal to which the transformed message might be routed by a PROPAGATE statement.
Out3 The third alternative output terminal to which the transformed message might be routed by a PROPAGATE statement.
Out4 The fourth alternative output terminal to which the transformed message might be routed by a PROPAGATE statement.
Note: For the syntax of the PROPAGATE statement, see PROPAGATE statement.

The following tables describe the node properties. The column headed M indicates whether the property is mandatory (marked with an asterisk if you must enter a value when no default is defined); the column headed C indicates whether the property is configurable (you can change the value when you add the message flow to the bar file to deploy it).

The Description properties of the Database node are described in the following table.

Property M C Default Description
Node name No No The node type, Database The name of the node.
Short Description No No   A brief description of the node.
Long Description No No   Text that describes the purpose of the node in the message flow.

The Database node Basic properties are described in the following table.

Property M C Default Description
Data Source No Yes   The ODBC data source name of the database in which reside the tables to which you refer in the ESQL that is associated with this node (identified by the Statement property).
Statement Yes No Database The name of the module within the ESQL file that contains the statements to execute against the database.
Transaction Yes No Automatic The transaction mode for the node. Valid values are Automatic and Commit.
Treat Warnings as Errors Yes No Cleared If you select this check box, database SQL warnings are treated as errors.
Throw Exception on Database Error Yes No Selected If you select this check box, database errors cause the broker to throw an exception.
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Copyright IBM Corporation 1999, 2007Copyright IBM Corporation 1999, 2007. All Rights Reserved.
This build: July 31, 2007 21:17:31

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