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Linking tables

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    #1

    Linking tables

    When is the best time to use referential integrity
    when using a one to many link between tables?
    Is there times that it should not be used?

    Thanks.
    Tags: None
    #2
    RE: Linking tables

    I use it all the time. There are different views on using integrity and probably many will tell you don't. From my experience with orphan children, I would much rather have the computer do a little extra work to make sure the chain does not break. I figure it's there for that purpose, why risk it?

    Now, on to why you shouldn't use it......

    Comment

      #3
      RE: Linking tables

      Glen,

      Referential Integrity serves a very real purpose. When refrential integrity is in place you can set the link to delete all child records when you delete the Parent. Or, to change the linking field in the child records when you change it in the parent.

      When Referential Integrity is turned off, the child records remain "independent" from the parent records, and deletes or changes do not occur in the child records.

      Comment

        #4
        RE: Linking tables

        Glen,

        I don't use referential integrity in most of my work. This can lead to orphaned child table records which can be a bit of a problem. There are easy work arounds however.

        It's my understanding that referential integrity will make it more likely that conflicts will occur during data entry in a multi-user setting, presumably because all the child table records have to be locked while the user is editing a parent table record.

        I don't permit the user to edit the link field values in my applications. So cascading changes aren't needed.

        If I need to delete all the linked child table records when the parent table record is deleted, I ask the user and then do it for him in Xbasic.

        My 2 cents. -- tom

        Comment

          #5
          RE: Linking tables

          Tom,
          I don't understand your position on this......Referential Integrity, when used properly, ELIMINATES the possibility of orphaned records that would be there without Referential integrity.

          for example: A sales order (header with detail records) is canceled.

          With referential integrity set, the user can delete the header, and the detail records would be deleted,automatically. Without referential integrity, either the user would have to delete the header, AND each detail record, proactively; or developer would have to do a lot of unnecessary coding to allow the user to delete the child records!!

          Comment

            #6
            RE: Linking tables

            Ray,

            I'm not sure I can articulate it any better. Guess I have a contrarian streak in me... or maybe it's a control freak streak... who knows?

            Here's what I was thinking. If it doesn't make sense, don't worry, I'm not recommending it to others, just explaining how I do it.

            1. In my applications I do not permit the user to change the link field values that tie all my sets together. So referential integrity doesn't help me with changes, even if it were enabled. There aren't any changes allowed, so there's never anything to cascade from parent to child tables.

            2. All of my applications have to run in multi-user environments, so I'm always trying to place the smallest possible load on the network. I'm also trying constantly to minimize network collisions that happen when two or more stations try to work with the same record at the same time. It's my understanding that referential integrity forces Alpha Five to lock all the linked child table records (not just the current record in each child table) whenever edits are happening in the parent table. I am able to avoid that by not using referential integrity.

            3. The trade off for what I think is marginally better performance is that I will get orphaned child records from time to time whenever the user deletes a parent table record. In most of my apps parent table records are not deleted frequently. If I run reports against the child tables I use the exist() function to filter out children who don't have parents. Otherwise, I let the orphans continue to exist in the child tables, and little harm is done since disk space is cheap. In rare instances where the client wants to delete child table records at the same time as a parent record, I popup a little dialog to verify that, and if they confirm the deletes, I use a simple xbasic script to delete the child records that would otherwise become orphans.

            I know this is more work, but in my particular applications it's working well. Please don't think I'm urging others to abandon referential integrity. I'm just suggesting that folks think about the pros and cons before assuming it's the only way to go.

            -- tom

            Comment

              #7
              RE: Linking tables

              Hi all,

              It is an interesting issue which is why it keeps popping up.

              My take on this is that I find referential integrity necessary whenever users must be able to change the linking key value in the parent. Referential integrity maintains the link to the child records.

              But in many cases you can use a linking key which users can't touch in which case the costs of Ref. Int. can be avoided, not that they are large as Tom points out.

              Bill
              Bill Hanigsberg

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