Constant Object

What is a constant?

A constant is a design object that holds a literal value that can be called from any expression. Constants allow you to define a value once—such as a company name, a key date, or a web service endpoint—and reuse it across multiple objects in an application. Using constants makes applications easier to maintain, as you only need to update the value in one place to have it reflected everywhere.

A constant can be referenced in other objects. To learn about referencing constants and other objects, see Referencing Objects in Expressions.

When to use a constant

Use a constant when you need to:

• Store reusable values: Define a value once and reference it across multiple expressions and objects in an application.
• Centralize updates: Update a value in a single location and have the change reflected everywhere the constant is used.
• Define environment-specific values: Configure values like usernames or endpoints that change between development, test, and production environments.

Elements of a constant

A constant contains the following elements:

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#	Element	Available Actions
1	Create Options	Choose to create a new constant from scratch, or create a duplicate of an existing constant.
2	Name	Enter a name for the constant. This name is used when calling the constant from an expression. We recommend following the Standard Object Names convention. Note that certain constant names are reserved for system use.
3	Description	Enter a description for the constant.
4	Type	Select the data type for the constant. Select the Array checkbox to store a list of values of the same data type.
5	Value	Define the literal value that is returned when the constant is called.
6	Environment Specific	Select this checkbox to prevent the constant's value from being updated on import, unless you've specified a value in an import customization file. You can only select this checkbox for constants that are a primitive data type or Email Address type. Constants should only be environment specific when their values are different based on the environment they are in. For example, a web service endpoint.
7	Save In	Select the folder where the constant should be created.

Reserved constant names

Certain names are reserved for system use and cannot be used as constant names.

The following reserved constant names are primarily used for process report metrics:

• Completion
• is_process_ontime
• is_process_overdue
• is_task_favorite
• is_task_ontime
• is_task_overdue
• Lag
• NetCompletion
• NetLag
• NetWork
• process_completion_time
• process_deadline
• process_ee_id
• process_start_time
• process_status
• pm_avg_completion
• pm_avg_lag
• pm_avg_work
• task_assignee_owner
• task_assignment_time
• task_attributed_to
• task_avg_completion
• task_avg_lag
• task_avg_work
• task_completion_time
• task_deadline
• task_ee_id
• task_status
• total_completion_time
• total_lag_time
• total_work_time
• Work

Constant security

Object security for constants is configured through role maps. By default, constants inherit the security of the folder that they are saved in. After creating a constant, you can disable that inheritance and modify the constant's security. See Editing Object Security to modify a constant's security.

The following table outlines the actions that can be completed for each permission level in a constant's security role map:

Actions	Administrator	Editor	Viewer	Deny
Evaluate the constant	Yes	Yes	Yes	Yes
View the constant definition	Yes	Yes	Yes	No
Duplicate the constant	Yes	Yes	Yes	No
Update the constant definition*	Yes	Yes	No	No
View the security	Yes	Yes	No	No
Rename the constant	Yes	Yes	No	No
Delete the constant	Yes	No	No	No
Update the security	Yes	No	No	No

Common constant options

A constant supports the following common design object options:

• Versioning: Constants support versioning.
• Renaming: Constants can be renamed.
• Viewing Appian design guidance: Constants support Appian design guidance.
• Duplicating: Constants can be duplicated.
• Object overwrite protection: Constants support object overwrite protection.

The following option is not available for constants:

• Viewing performance details: Constants do not support viewing performance details.

To view options available from the toolbar in Appian Designer, see Common view elements.

Create a constant

Constants of deprecated types cannot be created except by duplicating a constant of that type.

To create a constant:

1. In your application, go to the Build view.
2. Click NEW > Constant.
3. Configure the constant properties.
4. Click CREATE.

Edit constant properties

To edit a constant's properties:

1. In your application, go to the Build view.
2. Select the constant name to open it. This displays the Constant Properties dialog.
3. Edit the constant properties as needed.
4. Click SAVE.

Each time you modify and save a constant, a new version is created. All objects that use the constant will use the latest version. All versions are accessible to developers who can view the constant, and a constant can be reverted back to a previous version at any time.

Duplicate a constant

To duplicate a constant:

1. In your application, go to the Build view.
2. Select the checkbox next to the constant you want to duplicate.

3. Click DUPLICATE.

   

4. Update the duplicated constant properties as needed.
5. Click CREATE.

Move a constant

Users with Administrator permission to this object or rule folder can move it to another folder:

1. Navigate to the parent folder that the object or folder is in.
2. Select the object or folder. You can select more than one.
3. Click the Move button on the toolbar. The Move Objects dialog appears.

4. Use the folder picker or browser to select the new parent folder.

   Tip:  You can also create a new folder in the browser, if you have Editor permissions to its parent folder.

5. Click Move.

Delete a constant

Deleting a constant prevents users from further viewing or editing it. However, the last version of the constant is still available to be used in processes, record views, and interfaces. Appian does not recommend deleting constants that are in use because the constant can no longer be exported.

To delete a constant:

1. In your application, go to the Build view.
2. Select the checkbox next to the constant you want to delete.
3. Click DELETE. System administrators can delete multiple objects at once.

4. In the Delete Constant? dialog, ensure there are no objects that depend on the constant.

   Note:  If there are objects that depend on the constant, then deleting the constant will cause an error to appear in those objects.

5. Click DELETE.

Constant related resources

• Expression Rules: Constants are frequently used within expression rules to avoid hard-coded values.
• Referencing Objects in Expressions: Constants can be referenced using the cons! domain.
• Update Constant Smart Service: Constants can be updated programmatically within a process using this smart service.

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