[GitHub] khos2ow commented on issue #2584: Enhance and cleanup DatabaseUpgradeChecker

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khos2ow commented on issue #2584: Enhance and cleanup DatabaseUpgradeChecker
URL: https://github.com/apache/cloudstack/pull/2584#issuecomment-382824247
 
 
   @rafaelweingartner Adding a new schema upgrade path was really cumbersome and error-prone, because we needed to maintain a flat map of versions and their corresponding list of upgrade paths (`DbUpgrade`). Instead I'm proposing to have a logical hierarchy structure of versions:
   
   ```
   DatabaseVersionHierarchy.builder()
       .next("4.0.0"   , new Upgrade40to41())
       .next("4.0.1"   , new Upgrade40to41())
       .next("4.0.2"   , new Upgrade40to41())
       .next("4.1.0"   , new Upgrade410to420())
       .next("4.1.1"   , new Upgrade410to420())
       .next("4.2.0"   , new Upgrade420to421())
       ...
       .next("4.2.1"   , new Upgrade421to430())
       .next("4.9.3.0" , new Upgrade4930to41000())
       .next("4.10.0.0", new Upgrade41000to41100())
       .next("4.11.0.0", new Upgrade41100to41110())
       .build();
   ```
   
   With this approach, when we need to add a new version upgrade path, rather than add that (e.g. `Upgrade41200to41300`) in **dozens** of places, we only need to add it in *correct* place in the hierarchy. It will be even backward compatible, it means that we can inject a version in the middle of the hierarchy as well (e.g. between existing `4.9.3.0` AND `4.10.0.0`).
   
   As for your next question, originally I had it based on `master` but I figured it's good to have it on `4.11` forward, so I rebased it on 4.11 and waited for this exact discussion to mention what you mentioned. I even created another branch to target `master` with exact same fix. So we have two options, either apply this (with additional path) on `master` first, then apply this on `4.11` and when merge forward pretty much nothing will happen. Or apply this here and add extra path on master on another super-small PR.
   
   BTW there's a small logical problem which will be fixed in couple minutes! (that's why Travis fails now)

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