RevMedia

John Parr of Progressive Computer Solutions in Basingstoke queried how to get the system to produce RLIST sentences from stored data, in the way achieved by the query window. Whilst investigating this, it became apparent that QUERY.SUB (the routine used by the system to accomplish the \ Query functionality) has application for all developers. Its usage is therefore covered in this article.

Release 1.1 introduced "Query" technology, whereby the user could type in \ at the key prompt and convert the window into a query window. It also introduced the frequently overlooked \\ which permits the user to call back the set of parameters used in the last query operation, modify and then rerun them.

COMMON /LCQUERY.MODE/

There are a number of labelled common areas maintained by the system for its own use. As these are labelled common the developer has access to them. Query uses an area called LCQUERY.MODE which has three variables associated with it

     FLAG       This seems only to be set when the Query window is invoked
                with a \\ at which time it will contain \\ . It is
                subsequently cleared down and will therefore normally appear
                to be null.

     OLD_QUERY  Contains the information making up the previous query in a
                field mark delimited array, with each element of the array
                corresponding to a prompt on the window.

     TEMPLATE   The title of the query screen with which the current
                OLD_QUERY is associated.

Thus without interacting with QUERY.SUB at all it is possible for the developer to affect what will be displayed when the user enters \\ . Simply load OLD_QUERY with the query to be performed - in a layout corresponding to the screen layout rather than the normal layout of @RECORD. Thus if the company name were the second prompt on the screen, but field number four in the current record, to preset the query to look for all companies whose name began with A, OLD_QUERY would be loaded with @FM : "A]", and TEMPLATE with the Query window title.

QUERY.SUB takes two parameters, the first being a branch, but the second does not seem to be used. The possible branch values are DO.QUERY, CHECK.REDISPLAY, CUSTOMIZE, MAKE.SELECT and FILTER.SAVE. Those which the developer can use are documented below.

DO.QUERY

Calling QUERY.SUB with a branch label of DO.QUERY forces the window to enter query mode automatically. If the user selects any records using query, these records will replace the currently active browse list - without confirmation. This can be used to great effect by the developer if it is wished to reassign "Query Mode" to a softkey. The softkey could simply call a QUERY.SUB passing it DO.QUERY. Note that as mentioned above, if it is desired to use the same parameters as previously in the query (perhaps on a different softkey), the labelled common area FLAG must be loaded with \\ . Note further that if a record is currently displayed in the window and new records are chosen, it is the job of the developer to unlock the current record. The system will not do so.

MAKE.SELECT

This call is normally used to construct the RLIST sentence from the current query window contents and to perform the select statement thus constructed, returning an active select list. However it can be used by developers who wish to have the system construct RLIST statements for them from known data and make an active select list. The actual technique used is a little cumbersome but effective.

Essentially one needs to write a program that includes all of WINDOW_COMMON% but dimensions the WC_W% array to as many fields are there are to be in the select statement. WC_W%<2> must be loaded with the dictionary names to use and @RECORD must be loaded with the comparisons. Then QUERY.SUB is called passing it MAKE.SELECT and an active select list is returned. To illustrate this, try out the code segment below.

Examine the TCL stack to see how QUERY.SUB has constructed the select statement.

CUSTOMIZE

Customize is normally used within the query window to call the QUERY.SELECT/ command window for customising RLIST.SELECT and RLIST.SORT. It is possible to define (in @ENVIRON.SET<57> and <58>) a code and command to be called in place of the customize window. If this is done, the select and sort statement generated by QUERY.SUB will be passed to the alternative routine in @PSEUDO<1> and <2> respectively.

Thus if it was required to generate the select statement BUT NOT run it, the code above would be used, but with the following changes. @ENVIRON.SET would be temporarily modified to call a routine to capture @PSEUDO. QUERY.SUB would be called with CUSTOMIZE, then @ENVIRON.SET would be restored.