Creating ESQL for a node

The message flow opens in the Message Flow editor.

If you have already created the file, it is opened in the editor view and a new module is created and highlighted.

The following module is created for a Compute node:

CREATE COMPUTE MODULE module_name
       CREATE FUNCTION Main() RETURNS BOOLEAN
       BEGIN
              -- CALL CopyMessageHeaders();
              -- CALL CopyEntireMessage();
              RETURN TRUE;
       END;

       CREATE PROCEDURE CopyMessageHeaders() BEGIN
              DECLARE I INTEGER 1;
              DECLARE J INTEGER CARDINALITY(InputRoot.*[]);
              WHILE I < J DO
                     SET OutputRoot.*[I] = InputRoot.*[I];
                     SET I = I + 1;
              END WHILE;
       END;

       CREATE PROCEDURE CopyEntireMessage() BEGIN
              SET OutputRoot = InputRoot;
       END;
END MODULE;

The module name is determined by the value that you have set for the corresponding node property. The default name is message_flow_name_node_type. The main function contains calls to two procedures (described in the following list) that are declared in the Compute node module following the function Main. These calls are commented out. To include the function that they provide, uncomment the lines and place them at the appropriate point in the ESQL that you create for Main.

CopyMessageHeaders

This procedure loops through the headers contained in the input message and copies each one to the output message.

CopyEntireMessage

This procedure copies the entire contents of the input message, including the headers, to the output message.

If you create an ESQL module for a Database node, the following module is created:

CREATE DATABASE MODULE module_name
       CREATE FUNCTION Main() RETURNS BOOLEAN
       BEGIN
               RETURN TRUE; 
       END;
END MODULE;

For a DatabaseInput node, the module that is created contains three procedures, ReadEvents, BuildMessage, and EndEvent. Each of these procedures contains boilerplate text, which describes how the procedure works. For more information about configuring DatabaseInput nodes, see Configuring a DatabaseInput node. For a DatabaseInput node, the following first line of the module is created:

CREATE DATABASEEVENT MODULE module_name

For a Filter node, the module is identical to the module created for the Database node, except for the first line, which reads:

CREATE FILTER MODULE module_name

For Compute, Database, or Filter nodes, start by adding ESQL statements in the Main function, (after the BEGIN statement, and before RETURN TRUE). For DatabaseInput nodes, add ESQL statements in the ReadEvents, BuildMessage, and EndEvent procedures. You can add DECLARE statements in the module that are not within the Main function. To add a new line into the file, press Enter.

To help you to code valid ESQL, the editor shows a list of valid statements and functions at the point of the cursor. To start this assistance, click Edit > Content Assist. On some systems, you can use the key combination Ctrl+Space. Scroll through the list to find and highlight the statement or function that you want, and press Enter. The appropriate code is inserted into your module.

Content assistance works only if the ESQL can be parsed correctly. Errors such as END missing after BEGIN, and other unterminated block statements, cause parser failures and no content assistance is provided. Try content assistance in other areas around the statement where it does not work to narrow down the point of error. Alternatively, save the ESQL file; saving the file causes validation, and all syntax errors are written to the Problems view. Refer to the errors reported to understand and correct the ESQL syntax. If you use content assistance to generate most statements (such as block statements), these statements are correctly entered and there is less opportunity for error.