A common requirement in databound applications is to allow the user to view changes before they commit them to the database, showing the user both the original-old value along with the new. This gives users a chance to review their changes visually by comparing the old and new.
For an updated record that has yet been committed to the database, ADF BC stores both the old and new value. Among other reasons ADF BC does this, is it allows the user to cancel any changes, and rather than having to fetch the original value back from the database, ADF BC just retrieves the old value it has cached without a roundtrip to the database.
This cache gives us the ability to solve our original requirements as the ADF BC framework exposes methods to fetch both new and old non committed values from the Entity Object (EO). To fetch the new current value we call the associated accessor such as getPosition() or getName() that was automatically created by the framework in our EntityImpl. To get the old value we use the getPostedAttribute() method passing in the index of the field we wish to fetch.
In JDeveloper 11g through its introduction of Groovy expressions, it's very simple to expose the old value through the Entity Objects:
1) In your required EO create a transient attribute. For example if we want to show the old values for the Position attribute of our EO, we could create a new transient attribute named OldPosition.
2) Ensure the "Persistent" and "Derived from SQL Expression" properties are turned off for the new transient attribute.
3) Set the "Value Type" to Expression and enter the following Groovy expression into the Value field:
Note the call to the getPostedAttribute() method, passing in the index of the Position field that it requires.
If the Groovy syntax isn't familiar to you in JDeveloper 11g consult Grant Ronald's Introduction to Groovy.
A bad steer here maybe to try and use ADF Groovy's oldValue and newValue methods. Unfortunately these are only available for Groovy expressions in EO Declarative Validators, not in transient attribute.
4) Expose the attribute through the associated View Objects (VO) if necessary.
At runtime you'll note that initially the OldPosition field shows what's in the Position field. When you change the Position field's value, the OldPosition remains at the pre-cached value. Finally on committing the changes to the database, the OldPosition value is overwritten with the new Position value.