You can link an external ID to a record ID in D365 FO. Together with the external ID, you can also link an external revision number to a record ID.
The application, as defined for the connector, is used to store the link between the reference table and record ID in D365 FO and the external ID and revision number.
If you:

• Export data, the applicable external ID or revision is searched for in the target connector application. If a record exists for the reference table and the source field (RecId) combination, the external ID or revision of this record is as the output value of this option.
• Import data, the applicable target record ID is searched for in the source connector application. If a record exists for the combination of reference table and external ID and revision, the reference record ID of this record is the output value of this option. If no record exists for the combination, a record is created. The reference record ID of this record is the output value of this option.

Note: 

• You can only link an external ID or revision number to a record ID if, on the applicable document, the External reference field and the Revision field are filled in for the source field or target field of the current field mapping.
• You can only link a revision to a record ID in D365 FO if you also link the external ID. The external ID field mapping must precede the revision field mapping.
• Usually, you use the External reference option on a field mapping where the source field (export) or target field (import) is the RecID.

Standard procedure

1.	Click Connectivity studio Integration Design.
2.	On the Message tab, in the list, find and select the desired message.
3.	Click Edit.
4.	In the Mapping section, in the Target record pane, in the list, find and select the desired target record.
5.	On the Mapping tab, on the Field mapping tab, in the list, find and select the desired field mapping.
6.	Click the Field options tab.
7.	Select the External reference check box.
8.	Define if the current field mapping sets the external ID or revision number.
	In the Type field, select an option.
9.	The table for the reference record ID. For export, it is the table of the source field. For import it is the table of the target field.
	In the Reference table field, enter or select a value.
10.	Close the page.

See also

• External references and revision numbers