What is External ID?When importing data into Force.com apps, you can use External IDs to prevent duplicate records from being created as a result of the import operation. It allows use of relationships defined in legacy systems when importing data into Force.com apps.
- It is a flag that can be added to a custom field to indicate that it should be indexed and treated as an ID.
- It is a user-defined cross-referenced field.
- It can be created for custom field type (Text, Number or Email ONLY).
- Each object can have up to 7 (seven) external Ids (as of Spring '15).
- Configure UPSERT action to traverse object relationships defined in your Force.com app, but use External Id's from legacy system to discover Force.com record ID's.
- It helps improve Report and API SOQL performance.
- It can be used with UPSERT DML operation to seamlessly integrate apps with other systems.
- No need to know Force.com record Id's to load data.
- Very convenient for data integrations and migrations.
What is UPSERT?UPSERT is an API function that combines INSERT and UPDATE into a single call. It uses an indexed custom field or External Id to determine whether to create a new object or update an existing object.
- If the External Id is not matched, then a new object is created.
- If the External Id is matched once, then the existing object is updated.
- If the External Id is matched multiple times, then an error is reported.
- Use UPSERT when importing data to prevent the creation of duplicates.