Loops repeat a step or a contiguous sequence of steps a number of times, or until a condition is met. You can iterate over the elements in an aggregate property — a Value List, Value Group, Page List, or Page Group.

This feature provides a limited form of enumeration or looping, similar to the "repeat until" or "do while" or "repeat from X to Y" structures of programming languages.

Repeating a single step using the loop field

Click the Loop button to access the details of the iteration. Use the pop-up dialog to indicate whether and how to repeat the step. You can cause the step to repeat a specific number of times, or until a specific result is reached. Click OK to save your edits and close the dialog.

Use the Repeat selection box to apply the step to more than one page or object. Select:

• For each top level page
• For each embedded page
• For each element in value list
• For each element in value group
• For loop

To exit the iteration before processing all elements in the iteration, complete a transition that is true after the last desired element is processed.

When processing the For loop or iterating over a Value List or Page List property, the parameter param.pyForEachCount holds the current iteration number. You can examine (but not alter) this value in the step. For example, to iterate only over the first ten pages or values, you can exit the iteration when pyForEachCount is greater than 10.

For each top level page

Select the For each top level page option to sequence through all pages of a specified class or classes and perform a method or instruction for each top level page. Leave the Step Page field blank. Each time the step repeats, the step's page changes.

For the optional Only Loop for Certain Classes parameter, enter a class or classes. (Click the Add Row icon to add more than one class.)

When Only Loop for Certain Classes is not blank, iteration processing skips over any page with a class that does not appear on the list, or is not derived from one of these classes.

Use the add row icon to add a class. You can rearrange the order by selecting the row number and moving it up or down.

For each embedded page

Use For each embedded page option to apply a method or instruction to each embedded page in a Page List or Page Group property. Use the iteration choice to specify processing that is to occur for each embedded page. For example, you can:

• Copy each embedded page
• Delete each embedded page using Page-Remove
• Delete a property on each embedded page
• Add a property to each embedded page

and so on.

Identify the property containing the embedded pages in the Target field. The SmartPrompt list for the Target field shows only Page List and Page Group properties.

For the optional Only Loop for Certain Classes parameter, enter a class or classes. (Click the Add Row icon o add more than one class.)

• When Valid Classes is blank, all pages of the Page List or Page Group are included in the iteration.
• When Only Loop for Certain Classes is not blank, iteration processing skips over any page with a class that does not appear on the list, or is not derived from one of these classes.

For each element in a value list

Select the For each element in value list option to repeat the step for each element in a Value List property.

Each time the step repeats, the system applies a method or instruction of your choice (such as Property-Set) to the current property. Use the <CURRENT> index value to refer to the current property element.

When you select this iteration form, a Value List Property field appears. Identify the Value List property in the field.

For each element in a value group

Select the For each element in value group option to repeat the step for each element in a Value Group property.

When you select this iteration form, a Value Group Property field appears. Identify the Value Group property in the field.

Each time the step repeats, the system applies a method or instruction of your choice to the current property. Use the <CURRENT> index value to refer to the current property.

For loop

Select the For loop option to repeat the step a number of times determined by the values of integer constants or integer properties.

Enter integer constant values or integer property references for the Minimum Value, Maximum Value, and Increment fields. The Increment must be a positive integer.

The system accesses these three values once before starting the iteration. The iteration may occur zero, one, or many times, repeating until the incremented value is greater than or equal to the stop value (unless a transition causes processing to end earlier).

Understanding <CURRENT>

The symbolic reference <CURRENT> can be used only in the activity step that defines the iteration. If that step calls another activity, the symbolic reference <CURRENT> cannot be used in the called activity; rather, aspects of the current iteration are available on the parameter page of the called activity:

• For a repeat type of For each element in value list or For each element in value group, the symbol <CURRENT> refers to the value of ClipboardProperty corresponding to the iteration. For the called activity, this corresponds to the pyPropertyValue parameter described below.
• For a repeat type of For each embedded list, <CURRENT> refers to the ClipboardPage of the current iteration: for example, when used in an RUF call that takes a ClipboardPage parameter or on the right side of a property set when the target is a page (when you add to a page list using .list(<append>) ).
• For other repeat types, <CURRENT> refers to the index number of the current iteration, and corresponds to the pyForEachCount parameter.
• <CURRENT> can be used within the precondition and transition elements of a step that also includes a repeat element to evaluate the current element of the repeat.
• Within a repeat block, <CURRENT> can appear in the Expression Builder for the Target field of a Property-Set method; the keyword will refer to the current element’s property so that it can receive the new value.

Multistep loops

The scope of a loop can be more than one step. The loop type and conditions are set in the first step of a multistep loop.

To create a multistep loop:

1. Identify the step that is to be first in the loop. Click Loop to access the pop-up dialog, and complete the loop details.
2. Complete information for the first step. Identify the step page. Optionally, you can leave the method blank.
3. Select the stage, open the right-click context menu, and select Add Child. The current step is renumbered as NNN.0, where NNN was the previous step number. The form changes to include a new later step NNN.1. The scope of the iteration is now both NNN.0 and NNN.1. This zero-numbered step is known as the parent step.
4. Complete NNN.1, a child step. Leave the Step Page field blank and the iteration criteria blank in most cases, to have the child steps operate on the step page identified in the parent step. Optionally, you can override this step page of a child step by entering one of the following:

• a top-level page (such as the primary page).
• a reference to a page relative to the step page of the parent.
• a reference to a Page List or Page Group property on the step page of the parent. (In this case, complete the For each embedded page iteration details for the child step.)

1. To create an iteration of more than two steps, click within the parent step NNN.0 again to make it active, and select the Add Child menu option gain.

Numbered child steps are executed in sequence NNN.0, NNN.1, NNN.2 ... then NNN.0 again, until the iteration ends or a transition causes a jump to a labeled step.

You can add addition child steps at the same level by placing the mouse pointer in the Description field and pressing the Enter key.

To convert an iteration sequence to comments, enter two slash characters // in the Label field of the parent step. The parent and all child steps become comments.

For an example of multistep and nested iterations, see the Pega Community article How to use multistep loops and nested loops in activities.

Nested iterations

By using the Add Child menu option on a child step numbered NNN.Z, you can create a nested iteration.

For example, clicking a child step numbered 14.8 converts this to 14.8.0, and inserts a second-level child step numbered 14.8.1. Complete the iteration conditions for step 14.8.0.

Use care in entering the Step Page for the parent step of a nested iteration (14.8.0 in this example). If you refer to an aggregate property (Value Group, Value List, Page Group or Page List), select a property that reside on the <CURRENT> step page of the parent's parent. (That is, the structure of the iteration must follow the structure of the page). Within a nested step that does not have a repeat element, <CURRENT> inherits the semantics of its parent step that does have a repeat element.

Restrictions

If a step is part of an iteration sequence, the method cannot be any of the following:

Parameters available to called activity

The Pega Platform automatically adds the following parameters to the parameter page of a called activity with a step that contains an iteration.

• pyForEachCount — Index of the current iteration, normally starting at 1 and incrementing by one. (If the iteration type is For loop, the starting value may be a value other than 1 and the increment may be a value other than 1.) This parameter is available throughout the iteration as well as in called activities.

• pyIterationType — Indicates the iteration type, internally represented by one of the constants page, embedded, propertylist, propertygroup, or repeat. (This parameter values are not available to other methods in an iteration step.)

• pyIterationTarget — Identifies the name or reference of the iteration. For page and repeat types, it is blank. For embedded, it is the step page reference. For propertylist or propertygroup, it is the property specified in the iteration. (This parameter values are not available to other methods in an iteration step.) (This parameter values are not available to other methods in an iteration step.)

• pyPropertyValue — Available only for propertylist and propertygroup iterations. The text value of the current property. (This parameter values are not available to other methods in an iteration step.)

• pyPropertyReference — Obsolete. Set to "???" for backward compatibility.

• pyPropertyType — Obsolete. Set to "???" for backward compatibility.