Old Value Argument

Use the Old Value Argument field to map a remote operation argument to a second (old) argument in update or delete operations. Only MBOs bound to JDBC data sources support the Old Value Argument.

When updating columns with operation argument values, or deleting rows based on operation argument values, use the Old value argument field to access column values known to the device before changes. For example, if you use an update operation to modify the value of the lname column from Jones to Smith, the argument value is Smith, and if you choose to, you can map the Old value argument to Jones.

The old value is available from a drop down list, in the form old.argument_name (where argument_name is the name of the original argument, lname in the above example. The Un-map option unmaps the old value.

The old value argument does not support bigstring or bigbinary datatypes.

The Old value argument field is available from a number of Properties view locations, including:

Default Values horizontal tab of the Input vertical tab.
Operation Editing dialog.
Test execute dialog supports selection of old.argument parameters when testing update and delete operations.

Avoiding synchronization conflicts with the old value argument

If a mobile business object (MBO) performs an update or delete operation, the device sends additional parameters to the server that contain the original values of the database columns mapped to the object's parameters. These original values are shared with the enterprise information system (EIS) server in specially-named arguments. That is, if an argument is named A, and if the original value is available, it is provided in the argument named old.A. By checking whether or not the original value has become stale, the EIS operation can avoid conflicting updates, also known as Optimistic Concurrency Control (OCC).

Old value argument with an Update operation

Consider a database that contains table Person with three columns: socialsecurity_num (pk), fname, and lname. Then consider what happens in case of updates by different device applications.

Two devices, D1 and D2, have downloaded a row 999-55-1212, 'Joe', 'User'.
D1 updates the fname to Jane and succeeds.
D2 updates lname to Yooser, and consequently supplies the original values Joe and User.

Because the current lname (Jane) is not same as old.fname (Joe) the update for D2 does not occur.

Old value argument with a Delete operation

This example illustrates the steps for support of the delete operation old value argument:

Create an MBO from a JDBC data source using this SQL statement:
```
SELECT * FROM contact
```

Create a Delete operation defined as:

DELETE FROM sampledb.dba.contact
WHERE (id = :id)
 AND (:first_name IS NOT NULL)
 AND (first_name = :old.first_name)

Deploy the MBO and create a client application that loads all data from the enterprise information system (EIS) to the client.
For a given row, for example, id=1, client one modifies first_name (Jane) to Mary.
Client two fails when attempting to delete the changed row whose id=1, since the first_name has changed.