Key Mappings

Correlating Source and Target records

Correlation of source and target records is a key issue with many migration projects. Most source records have a unique identifier, but often this will not be the same on the target. So to correlate, we need to identify the fields on the target that can be mapped in Precision Bridge, so that for a given source record we can identify the correlated target record. This is what defining key mappings is all about.

The primary reason for identifying the key mappings is to determine if the migrated records should be created new on the target (an insert) or update an existing target record.

The Reference Mapping Type also relies on a key mapping having been defined. More on this later.

Defining Key Mappings in Precision Bridge

In defining a Form Mapping, you will first need to map the fields (on the Field Mappings tab). The key mappings will be a subset of these defined field mappings, and are defined on the Key Mappings tab.

If you specify 'No Key Mappings', this will usually mean that all records migrated will be new ones. So if you run the migration multiple times, you will get duplicates. 

Reference Mappings and Key Mappings

As mentioned earlier, key mappings are what reference field mappings use to correlate a referenced source record with a referenced targe record. A reference field mapping will refer to the key mappings of an earlier form mapping in calculating how to obtain the id of a target record from the id of a source record. In the example below, the assigned to value on the target is obtained using a reference mapping.

Reference mappings are really useful and extensively used. It is recommended that you get familiar with how they work. A detailed worked example can be found here: Reference Form Mappings - Overview and Worked Example

Special Case: Service Now Instance Migration

By default, for Service Now -> Service Now migrations, where scripted import sets are used to migrate and the sys_id is to be maintained, the sys_id will automatically serve as the correlation field. Therefore, even if you don't explicitly select key mappings, a record found with the same sys_id as the source will be updated.

If you do define key mappings, an update will be performed if key mappings match OR if a record is found with the same sys_id.