Field Maps and Coalesce are essential concepts in ServiceNow data management, particularly when working with Import Sets and Transform Maps.
Field Maps define the relationship between source data columns and target table fields during data imports. When you import data into ServiceNow using Import…Field Maps and Coalesce are essential concepts in ServiceNow data management, particularly when working with Import Sets and Transform Maps.
Field Maps define the relationship between source data columns and target table fields during data imports. When you import data into ServiceNow using Import Sets, the system first loads the data into a staging table. Transform Maps then use Field Maps to specify how each source column should map to the corresponding destination field in the target table. You can create automatic field mappings based on matching column names, or manually define custom mappings for more complex scenarios. Field Maps also support scripting, allowing you to manipulate data during the transformation process through onBefore and onAfter scripts.
Coalesce is a powerful feature that determines how imported records interact with existing records in the target table. When coalesce is enabled on a field mapping, ServiceNow uses that field as a unique identifier to find matching records. If a match is found, the system updates the existing record rather than creating a duplicate. If no match exists, a new record is created. You can set coalesce on multiple fields simultaneously, requiring all coalesced fields to match for an update to occur.
For example, if you are importing user data and set coalesce on the email field, ServiceNow will search for existing users with matching email addresses. Matching records get updated with the new import data, while unique email addresses result in new user records.
Best practices include carefully selecting coalesce fields that truly represent unique identifiers, testing transforms in non-production environments first, and using the Transform Map preview feature to verify mappings before processing large data sets. Understanding these concepts ensures clean data migrations and prevents duplicate records in your ServiceNow instance.
Field Maps and Coalesce in ServiceNow
Why Field Maps and Coalesce Are Important
Field maps and coalesce are essential components of ServiceNow's Import Set functionality. They enable organizations to efficiently import data from external sources while maintaining data integrity and preventing duplicate records. Understanding these concepts is critical for any ServiceNow administrator managing data migrations, integrations, or regular data imports.
What Are Field Maps?
Field maps define the relationship between columns in a staging table (import set table) and fields in a target table. When data is imported into ServiceNow, it first lands in a staging table. Field maps then specify how each column in the staging table should map to corresponding fields in the destination table.
Types of Field Mapping: - Auto Mapping: ServiceNow automatically matches fields with identical names between source and target tables - Manual Mapping: Administrators explicitly define which source column maps to which target field - Transform Scripts: Custom scripts that manipulate data during the mapping process
What Is Coalesce?
Coalesce is a field map property that determines whether a field should be used to identify existing records in the target table. When coalesce is set to true on a field map, ServiceNow uses that field's value to search for matching records.
How Coalesce Works: - If a matching record is found based on coalesced fields, the existing record is updated - If no matching record is found, a new record is created - Multiple fields can have coalesce set to true, creating a compound match condition
How Coalesce Operates in Practice
Consider importing user data where the email field has coalesce enabled:
1. Import set receives new row with email: john.doe@company.com 2. Transform map processes the row 3. ServiceNow searches the User table for records where email equals john.doe@company.com 4. If found: Updates the existing user record with imported data 5. If not found: Creates a new user record
Key Configuration Points
- Coalesce fields should contain unique identifiers or business keys - Common coalesce fields include: email, employee ID, asset tag, or sys_id - Setting coalesce on non-unique fields may cause unintended updates to multiple records - At least one field should typically have coalesce enabled to prevent duplicate records
Transform Maps and Field Maps Relationship
Transform maps contain field maps and define the overall transformation rules: - Transform Map: The parent configuration linking source to target table - Field Maps: Individual mappings within the transform map - Each field map can have its own coalesce setting
Exam Tips: Answering Questions on Field Maps and Coalesce
Key Concepts to Remember:
1. Coalesce = Update vs Insert Logic: When you see questions about preventing duplicates or updating existing records, think coalesce
2. Multiple Coalesce Fields: When multiple fields have coalesce enabled, ALL coalesced fields must match for a record to be updated (AND logic)
3. No Coalesce = Always Insert: If no fields have coalesce enabled, every import creates new records
4. Field Map vs Transform Map: Remember that field maps exist within transform maps - transform maps define source and target tables, field maps define column-to-field relationships
5. Staging Table Purpose: Data always goes to a staging table first, then transforms move it to the target table
Common Exam Scenarios:
- Questions asking how to prevent duplicate records during import: Answer involves coalesce - Questions about updating existing records: Coalesce on unique identifier fields - Questions about data transformation order: Import Set → Staging Table → Transform Map → Target Table
Watch Out For:
- Trap answers suggesting coalesce on sys_id when importing from external systems (external data typically lacks ServiceNow sys_ids) - Questions mixing up import sets, transform maps, and field maps - know the hierarchy - Scenarios where coalesce is set on non-unique fields, which would cause unpredictable updates