V4RB examples

[Erik Mueller-Harder]

Tim Lambert wrote:

> Hi Can anyone help with a beginner's desire to figure out a 1 to
> many set up (for RB 5.2)?  I can get Valentina working easily
> with a single table but the 1 to many example just doesn't happen
> for me. Is there a better set of examples I could learn from
> anywhere ? I'm sure is a simple thing to get the many table to
> track the linked 'ID' field but....how?

Sure!

The magic is in the "object pointer" field in your many table; set it up correctly, and you hardly have to think about the relationship again.  The Valentina Kernel documentation explains the setup pretty simply on page 39; also see pages 56-58 of the V4RB reference.

In short, though, just set up an object pointer field in a constructor function of your many table like this:

    fieldName = new VObjectPtr("fieldName",
    database.baseObject("oneTable"), kV_Restrict)

(all on one Rb line, of course, where "fieldName" is whatever you want to call your pointer field and "oneTable" is the name of the one-table you're relating back to).  The field on "oneTable" that you're relating to is the "recID" field, whose value you have no control over -- it's automatic.

kV_Restrict, kV_Cascade, and kV_SetNull (choose one!) define what will occur to the records on the many table when the single record they're related to on the one table gets deleted:

kV_Restrict means you canNOT delete the one record if related many records exist.

kV_Cascade means that all the related records on the many table get deleted when you delete the one record.

kV_SetNull means that the many records get their objectPtrs set to 0 if the related one record gets deleted -- they're orphaned, in other words.

If you have a "one" table called "personBO" and a "many" table called "taskBO", it might look like this:

    PersonBO         TaskBO
    --------         ------
    recID <--------- personPtr
    firstName        taskDate
    lastName         taskTime
                     taskDescription
    
After creating a record on PersonBO, create as many records on TaskBO as you need, populating personPtr with recID from personBO (watch line breaks!):

    personCursor = db.SQLSelect("select recID, * from personBO
    where recID = 0, kV_Server, kV_ReadWrite, kV_Random)

    personCursor.varCharField("firstName").value = "Erik"
    personCursor.varCharField("lastName").value = "Mueller-Harder"
    if not personCursor.Update then
    // error handling here
    end if

    taskCursor = db.SQLSelect("select * from taskBO where
    recID = 0, kV_Server, kV_ReadWrite, kV_Random)

    taskCursor.objectPtr("personPtr").value =
    personCursor.ULongfield("recID").value

    [populate other task fields here]
    
    if not taskCursor.Update then
    // error handling here
    end if

>From that point on, the data are related -- the relationship need not explicitly be referred to.  So:

    vc = db.SQLSelect("select firstName, lastName, taskDate from
    personBO, taskBO where lastName = 'Mueller-Harder'")

will give you a cursor containing all persons in personBO with the last name of Mueller-Harder, and all of their related tasks -- you can leave out the customary where clause " and taskBO.personPtr = personBO.recID" altogether.

I hope this is enough to get you started.

Erik