Iterate Loop

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Chapter 6 Grouping Activities : Iterate Loop

Iterate Loop

An Iterate loop repeats the series of grouped activities once for every item in an existing sequence or list. The list can be items of any datatype. The following is an example of an iterate loop.

The process performs the following operations:

1.

A JDBC Query activity is used to query a database and populate a list of customer records. The customer records are then passed to a group containing one activity, WriteCustomerList.

2.

The WriteCustomerList activity writes the name and address of each customer to a file, appending to the file as each record is written.

3.

The group iterates once for every customer record returned by the QueryCustomer activity, and transitions to the ReadCustomerList activity once the last record is processed.

4.

The process then reads the file that was written so that its data is available to the process, then transitions to a Send Mail activity to send the contents of the customer list by way of email.

The following is the configuration for this example:

In this example, the repeating element $QueryCustomer/Customer/Record is used to determine the number of iterations to perform. One iteration is performed for every element contained in the repeating element.

The Variable List field is an XPath expression. You can use a simple expression containing a complete list as in the example above, or your expression can be more complex and only process certain items in the list. For example, if you wish to skip over the first 10 records returned, the expression in the Variable List field would be the following:

$QueryCustomer/Customer/Record[position() > 10]

See Chapter 9, XPath for more information on creating XPath expressions.

Iteration Element

The Iteration Element field on the Configuration tab allows you to supply a name for a process variable containing the current iteration element. This allows you to easily map the value of the current iteration element instead of using predicates on the process variable used for iteration. When you specify a value for this field, a process variable with the specified name appears in the Process Data tree in the Input tab. For example, in the Iterate group above, we specified curent-record as the name for the current element. This causes the following to appear in the process data tree:

Notice that both $QueryCustomer/Customer and $current-record contain the element Record. $current-record/Record is a copy of the $QueryCustomer/Customer/Record[i] element, the current element being processed. If you use $QueryCustomer/Customer/Record[i] in an input mapping, TIBCO ActiveMatrix BusinessWorks traverses the $QueryCustomer/Customer/Record element to retrieve the current element each time the loop iterates. By using the $current-record/Record element instead, you save processes time in proportion to how many times the iteration loop repeats. The larger number of elements contained in the $QueryCustomer/Customer/Record repeating element, the greater the performance improvement you will notice by using $current-record/Record instead of $QueryCustomer/Customer/Record[i].