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## 18.5.8.4.5 ETag Support

Learn about ETag support.

When a BOSS business object defines a history attribute of type `historyType='versionNumber'` then the object will have an ETag returned in the response payload in the selector `$context.etag`. The BOSS adapter defines an `APEX$ETAG` column in the data profile mapped to this `$context.etag` selector, and including the Additional Information annotation tag of `ETag`. At runtime, the BOSS adapter will include a non-null ETag value with update and delete operations as expected by the BOSS runtime. When configuring APEX regions like form or interactive grid based on a REST Data Source for a BOSS object with an ETag, developers must set the Lost Update Type to the value Row Version Column and choose `APEX$ETAG` for the row version column name. Alternatively, to have BOSS perform the lost update protection only on the server-side, you can disable APEX's lost update protection on a form or grid region when it's using a REST Data Source for a BOSS object that has an ETag.

Parent topic: BOSS REST Data Source Runtime Features