Business Rules in ServiceNow

Business Rules :

• Business rules are the server side processing objects.  
• Can be configured to trigger on create/read/update/delete operations into a table.
• Can be configured to execute before/after/async of any of the the above operations.
• Before rules are generally used for data enrichment, validation.
• After rules are generally used to configure notifications, perform upsert operations into a related table.
• Async rules are generally used for outbound integrations, heavy processing logic which could  otherwise impact user experience. 
• Display rules can be configured to pass on values from server side to client side scripts to eliminate the round trips.
• Query rules can be configured to add additional default conditions to all the query statements performed on a table.

Objects : 

current  :  represents the current state of the record that is being processed.   Available in before, after, query, display, async business rules.

previous : represents the previous state of the record that is being processed. Available in before, after business rules.

g_scratchpad :   represents an object which can be loaded with key value pairs from server side to access at client side. Available in display business rules.

Avoid :

•  current.update()  in before business rules. Could lead to infinite loop of rule execution without  proper conditions. 
•  outbound integration calls in before/after business rules.  This impacts user experience.
•  writing lengthy scripts in advanced business rules . Use script includes instead.
•  Avoid global business rules. Use script includes where possible. 
• Avoid circular updates among related tables.  i.e Business rules on table A updating table B, and Business rules on table B, updating table A.

Stuck with ? :

Unique key violation detected by database :   Could be because of current.update() in before business rules, or circular updates.

Workflow execution order :  Workflows run before the insertion into table and after before business rules with order <= 1000.  so, adjust the order if needed.

Empty journal fields :  values of journal fields such as work_notes, comments are not available in an after business rules, use current.work_notes.getJournalEntry(1) instead. 

Activities being duplicated : Could be because of current.update() in before business rules, or circular updates between related tables.

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