NAME
Use NAME to define an alias (an
alternative name) by which a variable can be known.
Example 1:
-- The following statement gives
Schema1 an alias of 'Joe'.
DECLARE Schema1 NAME 'Joe';
-- The following statement produces
a field called 'Joe'.
SET OutputRoot.XMLNS.Data.Schema1 =
42;
-- The following statement inserts a
value into a table called Table1
-- in the schema called 'Joe'.
INSERT INTO Database.Schema1.Table1
(Answer) VALUES 42;
Example 2:
-- At Module scope define
ColourElementName and set it external
-- so that its default value of
'black' can be overridden as a UDP
DECLARE ColourElementName EXTERNAL
NAME 'black';
-- Use the ColourElementName in a
function
CREATE FIRSTCHILD OF
OutputRoot.XMLNSC.TestCase.ColourElementName
Domain('XMLNSC')
NAME 'Node1' VALUE '1';
If the owning message flow has been
configured with a UDP named ColourElementName of type String, which has been given the value red, the following output message is generated:
<xml version="1.0"?>
<TestCase>
<red>
<Node1>1</Node1>
</red>
NAMESPACE
Use NAMESPACE to define an alias (an
alternative name) by which a namespace can be known.
Example:
This example illustrates a namespace
declaration, its use as a SpaceId in a path, and its use as a character
constant in a namespace expression:
DECLARE prefixOne NAMESPACE
'http://www.example.com/PO1';
-- On the right hand side of the
assignment a namespace constant
-- is being used as such while, on the
left hand side, one is
-- being used as an ordinary constant
(that is, in an expression).
SET
OutputRoot.XMLNS.{prefixOne}:{'PurchaseOrder'} =
InputRoot.XMLNS.prefixOne:PurchaseOrder;
SHARED
Use SHARED to define a shared variable.
Shared variables are private to the flow (if declared within a schema) or node
(if declared within a module), but are shared between instances of the flow
(threads). No type of variable is visible beyond the flow level; for example,
you cannot share variables across execution groups.
Shared variables exist for the
lifetime of the:
- Execution group process
- Flow or node, or
- Node ESQL code that declares the variable
(whichever is the shortest). They
are initialized when the first message passes through the flow or node after
each broker startup.
You cannot define a shared variable
within a function or procedure.
The advantages of shared variables,
relative to databases, are that:
- Write access is much faster.
- Read access to small data structures is faster.
- Access is direct; that is, there is no need to use a
special function (SELECT) to get data, or special statements (INSERT,
UPDATE, or DELETE) to modify data. You can refer to the data directly in
expressions.
The advantages of databases,
relative to shared variables, are that:
- The data is persistent.
- The data is changed transactionally.
These read-write variables are ideal
for users who are prepared to sacrifice the persistence and transactional
advantages of databases in order to obtain better performance, because they
have a longer life than only one message and perform better than a database.
Because SHARED variables can be
updated by multiple additional instances, you must ensure that you do not
change SHARED variables that might cause unexpected results, for example, if
the variable is being used as a counter.
As SHARED variables are initialized
once on the first message through a node, it is possible to initialize a SHARED
ROW variable once with the results from a Database query. The following code
shows an example of this:
CREATE SCHEMA testSchema
DECLARE mySharedRow SHARED ROW;
DECLARE initialized SHARED BOOLEAN
myINIT();
CREATE COMPUTE MODULE testModule
CREATE FUNCTION Main() RETURNS BOOLEAN
BEGIN
SET OutputRoot.XMLNSC.Top.TEST.Result1
VALUE = initialized;
SET OutputRoot.XMLNSC.Top.TEST.Result2
= mySharedRow;
END;
END MODULE;
CREATE FUNCTION myINIT( ) RETURNS BOOLEAN
BEGIN
LOG EVENT VALUES('myINIT CALLED');
SET mySharedRow.Top[] = SELECT
A.MyCol1, A.MyCol2 from Database.Test AS A;
RETURN TRUE;
END;
You can prevent other instances
seeing the intermediate stages of the data by using a BEGIN ATOMIC construct;
see BEGIN ... END statement.
Your user program can make an
efficient read, or write, copy of an input message in the input node by using
shared-row variables, which simplifies the technique for handling large
messages.
Restriction:
Subtrees cannot be copied directly
from one shared row variable to another shared row variable. Subtrees can be
copied indirectly by using a non-shared row variable. Scalar values extracted
from one shared row variable (by using the FIELDVALUE function) can be copied
to another shared row variable.
