Originally from earlduque/ServiceNow-Developer-Training. Thanks Earl!

Business Rules in ServiceNow #

What is a Business Rule? #

Business Rules are server-side scripts that run by database operations (i.e. when database records are queried, updated, inserted, or deleted).

Business rules respond to database operations regardless of of access method, so it doesn't matter whether users interact with records through forms and list, web services, or data imports.

Business rules don't necessarily monitor forms, nor form fields, but will run if and when forms forms interact with the database when records are saved, updated or submitted.

ServiceNow offers over 2,400 out-of-the-box business rules and they're commonly used throughout the system.

Business rules give us access to:

  • Current object (current)
  • Previous object (previous)
  • Scratchpad (g_scratchpad)

⬆ What does this mean?
Let's say we have a Business Rule that runs when a new incident is inserted into the incident table. Think of that incident being the current object. To access the number assigned to the newly created incident, we can use current.number in a script. That's how we have access to a current object.

Business Rule Actions #

Business Rules can peform a variety of actions such as:

  • Changing values on a form that is being updated by the user. Field values can be set to specific values available for that field, values copied from other fields, and relative values determined by the role of the user.
  • Displaying information messages to the user.
  • Modifying values on child tasks when changes are made to parent tasks.
  • Preventing users from accessing or modifying certain form fields.
  • Setting a list of condition that, if met, will abort the current database transaction, thus preventing the user from saving the record to the database.

Administrators have the ability to set field values, create information messages, and abort transactions without the need to write a script

When should I use a Business Rule? #

Business rules are used for tasks like automatically changing values in form fields when specific conditions are met, or to create actions for email notifications and script actions.

The following options provided determine the time the business rule should run:

Option When the rule runs
Before After the user submits the form, but before any action is taken on the record in the database
After After the user submits the form, and after any action is taken on the record in the database
Async When the scheduler runs the scheduled job created from the business rule, the system will create a scheduled job from the business rule after the user submits the form and after any action is taken in the database
Display Before the form is presented to the user, just after the data is read from the database

The database operations that the system takes on the record:

Option When the rule runs
Insert When a user creates a new record and the system adds it to the database
Update When the user modifies an existing record
Query Before a query for a record or a list of records is sent to the database. Typically you should use query for a before business rule
Delete When a user deletes a record

Business Rule Operating Flow #

Below is an example of a Business Rule operating flow:
1. The user sends a request to the server for a specific incident (query).

2. Application server requests record from the database server.

3. The database server responds to the application server with the record.

4. The application server checks for display-business-rules, then sends the response back to the user. The display event will fire any existing display-business-rules.

5. User modifies incident record and sends update request.

6. Application server receives update, checks for before-business-rules, then sends to database server to be updated.

7. The database server updates the record.

8. Lastly, the application server checks for after-business-rules.

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Creating a Business Rule #

1. Log into your personal developer instance of ServiceNow.

2. Navigate to System Definition > Business Rules.

3. Click New.

4. A Business Rule runs a specific table. After naming your Business Rule, choose a table you wish to modify from the Table list.

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In this example, we are looking at a Business Rule that creates an asset on an insert. The table that this Business Rule will be modifying is the Configuration Items [cmdb_ci] table.

5. Afterwards, we have to specify when we want the Business Rule to run (i.e. before a record is inserted, after a record is inserted, etc.) The order will specify the order in which the Business Rule will run in.

6. Next, you have to select the conditions under which the Business Rule will run. There are two conditions: database operations, and custom conditions. Custom conditions will either allow you to choose from the Filter Conditions field shown at the bottom, or using a Condition script field under the Advanced tab.

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Note: In order to access the Condition script field, the Advanced checkbox on the upper right hand side of the form, under the Active checkbox.

Using the filter conditions allows you to automatically filter condition scenarios from lists they have provided (like UI policies).

If you are writing a custom script, you must specify the condition in which the Business Rule should run in the Condition field.

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(current.asset.nil() || (current.asset.ci != current.sys_id))

In this example, the condition will only run if the current asset is nil, or in other words, the current CI record does not have an asset associated with it OR if the current asset CI does not equal with the current_sys_id. When the condition evaluated to true, the script underneath the condition will run.

7. After everything on the form has been filled out, hit Submit.