The WHEN XFD directive is used when you want to include multiple record definitions or REDEFINES in a database table. It's typically used when you want to force certain columns to be built that wouldn't be built by default (because you want to use them from the RDBMS side). For more information, see REDEFINES Clause.
Recall that the key fields and the fields from the largest record are automatically included as explicit columns in the database table. All fields are stored and retrieved from the database, whether they appear as explicit columns or not. So you don't need to use WHEN unless you want to ensure that some additional fields are explicitly listed by name in the table. For details about how fields are included in the database table, see How XFDs Are Formed.
WHEN declares that the field (or subordinate fields, if it is a group item) that immediately follow the XFD directive must appear as a column (or columns) in the database table. It also states one condition under which the columns are to be used. The WHEN XFD directive guarantees that the fields are explicitly included in the table, as long as they aren't FILLER and don't occupy the same area as key fields.
The WHEN XFD directive results in a table that unites all fields subordinate to the WHEN XFD directive. This table might include more columns and could affect performance and storage requirements.
$XFD WHEN field = value (equals) $XFD WHEN field <= value (is less than or equals) $XFD WHEN field < value (is less than) $XFD WHEN field >= value (is greater than or equals) $XFD WHEN field > value (is greater than) $XFD WHEN field != value (is not equal to) $XFD WHEN field = OTHER
The value may be an explicit data value (in quotes). The word "OTHER" can be used only with "=". It means use the following field(s) only if the WHEN condition(s) listed at the level of this field are not met.
03 ar-code-type pic x.
$xfd when ar-code-type = "s"
03 ship-code-record pic x(4).
$xfd when ar-code-type = "b"
03 backorder-code-record redefines ship-code-record.
$xfd when ar-code-type = other
03 obsolete-code-record redefines ship-code-record.
OTHER may be used before one record definition, and may be used once at each level within each record definition.
01 ar-codes-record.
03 ar-codes-key.
05 ar-code-type pic x.
05 ar-code-num pic 999.
01 ship-code-record.
03 filler pic x(4).
03 ship-instruct pic x(15).
01 terms-code-record.
03 filler pic x(4).
03 terms-rate-1 pic s9v999.
03 terms-days-1 pic 9(3).
03 terms-rate-2 pic s9v999.
03 terms-descript pic x(15).
If you add the WHEN XFD directive as shown below, it causes the fields from the SHIP-CODE-RECORD to be included in the database table, and determines when specific database columns are used. The underlined fields then appear as columns in the database table:
01 ar-codes-record.
03 ar-codes-key.
05 ar-code-type pic x.
05 ar-code-num pic 999.
$xfd when ar-code-type = "s"
01 ship-code-record.
03 filler pic x(4).
03 ship-instruct pic x(15).
$xfd when ar-code-type = "t"
01 terms-code-record.
03 filler pic x(4).
03 terms-rate-1 pic s9v999.
03 terms-days-1 pic 9(3).
03 terms-rate-2 pic s9v999.
03 terms-descript pic x(15).
FILLER data items don't have unique names and are thus not used to form columns in the database table. You could use the NAME XFD directive to give them a name if you really need to see them in the database table.
In the following code, in which no WHEN XFD directives are used, the underlined fields are explicitly named in the database table. (Key fields have the suffix key in their names in this example.)
Note that REDEFINES records simply re-map the same data area and are not explicitly included in the database table by default:
01 archive-record.
03 filler pic x(33).
03 archive-code pic 9(6).
03 archive-location pic 9(2).
03 filler pic x(10).
01 master-record.
03 animal-id-key.
05 patient-id pic 9(6).
05 species-code-type pic 9(5).
05 species-name pic x(6).
03 service-code-key.
05 service-code-type pic 9(6).
05 service-name pic x(10).
03 billing-code.
05 billing-code-type pic 9(4).
05 plan-name pic x(8).
03 office-info.
05 date-in-office pic 9(8).
05 served-by-name pic x(10).
03 remote-info redefines office-info.
05 van-id pic 9(4).
05 proc-code pic 9(8).
05 vet-name pic x(6).
If you add the WHEN XFD directives shown below, you add several columns to the database table. The fields which then appear in the table are underlined:
$xfd when animal-id-key = "00000000000000000"
01 archive-record.
03 filler pic x(33).
03 archive-code pic 9(6).
03 archive-location pic 9(2).
03 filler pic x(10).
$xfd when animal-id-key = other
01 master-record.
$xfd use group
03 animal-id-key.
05 patient-id pic 9(6).
05 species-code-type pic 9(5).
05 species-name pic x(6).
03 service-code-key.
05 service-code-type pic 9(6).
05 service-name pic x(10).
03 billing-code.
05 billing-code-type pic 9(4).
05 plan-name pic x(8).
$xfd when billing-code-type = "1440"
03 office-info.
05 date-in-office pic 9(8).
05 served-by-name pic x(10).
$xfd when billing-code-type = other
03 remote-info redefines office-info.
05 van-id pic 9(4).
05 proc-code pic 9(8).
05 vet-name pic x(6).
If your application has a REDEFINES whose field names are more meaningful than the fields they redefine, you might consider switching the order of your code, rather than using a WHEN XFD directive. Use the less significant field names in the REDEFINES.
For example, you might change this:
03 code-info.
05 filler pic 9(8).
05 code-1 pic x(10).
03 patient-info redefines code-info.
05 patient-id pic 9(4).
05 service-code pic 9(8).
05 server-name pic x(6).
03 patient-info.
05 patient-id pic 9(4).
05 service-code pic 9(8).
05 server-name pic x(6).
03 code-info redefines patient-info.
05 filler pic 9(8).
05 code-1 pic x(10).
The fields that would appear in the database table by default are underlined above. This shows how the column names might become more meaningful when the order is reversed. Your application operates the same either way.
01 col-type pic x.
$xfd when col-type = "a"
03 def1 pic x(2).
$xfd when col-type = "b"
03 def2 redefines def1 pic 9(2).