Changes between Version 3 and Version 4 of BluePrintUpgrades

Timestamp:

02/13/16 16:15:25 (9 years ago)

Author:

Pat Tressel

Comment:

--

BluePrintUpgrades

@@ -12 +12 @@
 
 For other software, people are used to automatic upgrades.  Even the (very complex) Windows operating system auto-upgrades.
-What can make an Eden upgrade problematic?  There are two types of visible changes:
+What can make an Eden upgrade problematic?  There are two types of changes that are visible to the sysadmin or user:
 
 * Structural changes: These are changes that affect data structure and file layout.
@@ -21 +21 @@
   This would affect users, and might require retraining.
 
+These issues would be present even if the site were running an unmodified version of Eden using a supplied template.
+If the site has made modifications to the code, even in a template, and those modifications conflict with changes in
+the upgrade, then the two sets of modifications need to be reconciled.  Note configuration changes are expected, and
+need to be supported in the normal case above.
 
+Expected issues beyond the above, that can arise if the site has code modifications, are:
+
+* An API change may require the site to alter their code to use the modified API.
+* Alteration by the site of code outside of the site's template may lead to merge conflicts.
+* If both the site and upgrade have database schema changes, then those changes need to be reconciled and merged.
+
+Of these issues, the most potentially destructive is a database schema change, as without proper preparation,
+running the upgraded version of Eden can lead to data loss.  The Web2py migration does not understand changes
+such as renaming a column -- that is interpreted as deleting a column and adding a new one.  This can happen
+regardless of whether the site has made any changes whatsoever in their code.  Also, requiring the sysadmin to
+investigate the upgrade's schema changes, and write scripts to convert their database, is a significant burden.
+Addressing database migration is thus likely to be the largest reduction in upgrade effort.
+
+Support for upgrades can proceed in stages:
+
+* Deal with the case in which there are no significant site code changes.
+  That is, changes are limited to configuration and relatively cosmetic UI changes.
+* Assume additional changes are confined to the site's template, but may include use of a now-deprecated
+  or altered API.
+* Deal with site database schema changes.
+* Consider what can be done to ease conflict resolution in UI code.
+* Likewise, for conflict resolution in model and controller code, beyond schemas.
+
+Some potential conflicts may be avoided up front by convincing sites not to alter framework code, and to avoid
+directly editing models and controllers.  For changes that may be of benefit to other users, encourage sites to
+make their changes generic and contribute them back to the main repository.
+
+Here, we consider the first stage, in which the upgrade issues are due to changes in Eden rather than in site
+changes.  Since directory layout changes are rare, this can be deferred until such a change is planned.
+
+== Configuration Changes ==
+
+== Database Schema Changes ==
 
 ----
 BluePrints
+BluePrints