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Find / Delete Orphaned Records

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  • Find / Delete Orphaned Records

    Assume native Alpha Five tables
    Assume two table set, headers linked one-to-many to items (as you might find for an invoice, for example)
    Assume an arbitrary number of header records have been deleted

    Question: what's the fastest way to find and delete the orphaned one-to-many child records?


    -- tom

  • #2
    Re: Find / Delete Orphaned Records

    One would have to further assume that you do not have Referential Integrity to cascade deletes turned on.
    Or maybe you do and are looking for suspenders in addition to the belt.
    Either way, the key word in your question is "fastest".

    The thing that jumps to mind would be two lists each containing only the linking field one of the parent and the other of the child then use something like:
    Then you will end up with a list of all the linking field values of the child that do not have a parent.

    Another idea, is to create a reverse set. Initialize the set in an array. For each element of the array that is lacking a value of the linking field of the child (which is originally the parent) delete the corresponding record.


    • #3
      Re: Find / Delete Orphaned Records

      Thanks, G.

      I eschew the use of referential integrity.

      Have been using the reverse set idea, using a one-to-one link from items to headers, and it works well. At times, I've written custom scripts that step through the filtered header table, and for each I then delete all the linked children, before deleting the current header...

      Am wondering what approaches others have used, and which might be fastest.

      Thanks for responding.

      -- tom


      • #4
        Re: Find / Delete Orphaned Records

        I have used a couple of variations in the past
        My current weapon of choice (after the broadsword of course) is lightning fast so cant measure it, but has very simple code
        I run it in my index maintenance routine run when all tables are closed so I can pack at the same time.

        The key is that "invl_saved_orphans.dbf" is a simple linked table of invlines to invheader with only two fields, being the linking fields invseq (the second one named invseq1 automatically.


        • #5
          Re: Find / Delete Orphaned Records

          Thanks Ray. Not sure what "a simple linked table" might mean?

          This sounds like the reverse set idea G and I mentioned above, but you are using the table object... puzzling.


          • #6
            Re: Find / Delete Orphaned Records

            Never used it but wouldn't a delete/mark operation using the exist() function as a filter work?



            • #7
              Re: Find / Delete Orphaned Records

              Sincere apologies Tom
              It's properly called "a Mapped table"
              It is a useful tool in that the dbf is acted on as a standard dbf referring to the field names without a tablename->
              It allows only 1-1 link and the main feature (for certain purposes only) is beneficial here in that changes can only effect the primary table.
              It's extremely useful for when you need a flat join without physically creating an intermediate table or operation (but then I never use operations either so that may be another way).


              • #8
                Re: Find / Delete Orphaned Records

                Andrew, I did that for a try - definitely feel a little hiccup time wise in the same application. Maybe I didnt do it the best way.

                Once the table is defined it does stay there, but its a wizz to, for example, update all line prices to stock master price change, it uses up imperceptible space
                Another to pop-up a query of all like items occurring in and order system. I am a bit slow discovering stuff and only discovered it a couple of months ago. it uses up imperceptible space resources as far as I can see.


                • #9
                  Re: Find / Delete Orphaned Records

                  Originally posted by Ray in Capetown View Post
                  Andrew, I did that for a try - definitely feel a little hiccup time wise in the same application.
                  After posting I wondered if the delete operation would open and close the index file referenced in the exist() function for each record of the table. That is probably what is generating the time delay hiccup.


                  • #10
                    Re: Find / Delete Orphaned Records

                    There is a fair amount of code I noticed, cant check now I deleted the op.


                    • #11
                      Re: Find / Delete Orphaned Records

                      Without testing for time, I believe if you load the child table in a text file (in memory) then use word_subtract() to remove the orphan records (use a list of the parent's linking field, also loaded in memory) then completely delete (zap) the child and then populate the child from the text file, that might be the fastest as you are not iterating over the records and deleting one at a time. You just wipe the slate clean, remove the orphans then populate the table.


                      • #12
                        Re: Find / Delete Orphaned Records

                        Thanks for all the ideas and suggestions. Since there's very little overhead associated with set definitions I'll probably be sticking with the reverse set approach, at least for now. Thanks again.


                        • #13
                          Re: Find / Delete Orphaned Records


                          Don't know if you've done any work with collections. I find <COLLECTION>.EXIST() to be the fastest test in a filter.


                          Add some orphan records to the dtls table and then delete them with the button on the "main" form.
                          There can be only one.


                          • #14
                            Re: Find / Delete Orphaned Records

                            Interesting! Time to crack open the books....


                            • #15
                              Re: Find / Delete Orphaned Records

                              My example probably doesn't follow the spirit of how collections are meant to be constructed but the functionality is used.
                              There can be only one.