From f2e6cceaa8a8dd4b2cc2e2777980c45a42ef9624 Mon Sep 17 00:00:00 2001
From: Michal Kleiner <michal.kleiner@chrometoaster.com>
Date: Fri, 30 Apr 2021 00:24:41 +1200
Subject: [PATCH 1/2] Update the migration script to better handle fresh and
 empty installs

---
 src/Dev/AT4xMigrationTask.php | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/src/Dev/AT4xMigrationTask.php b/src/Dev/AT4xMigrationTask.php
index 5575ae3..2857e33 100644
--- a/src/Dev/AT4xMigrationTask.php
+++ b/src/Dev/AT4xMigrationTask.php
@@ -21,6 +21,7 @@ class AT4xMigrationTask extends BuildTask
 
     protected $description = 'Migrate AT db data from version 3.x to version 4.x';
 
+    protected $basicFields = ['ID', 'RecordID', 'Version'];
 
     /**
      * Static run wrapper with a dummy request
@@ -68,6 +69,14 @@ public function run($request)
             return;
         }
 
+        // Skip migration if there's no data at all
+        if (($baseObjectsCount == $baseTermsCount) && ($baseObjectsCount == $termsCount) && ($baseObjectsCount == 0)) {
+            DB::get_schema()->alterationMessage("There's no data to migrate, skipping the migration.", 'notice');
+            DB::get_schema()->alterationMessage('If you want disable the migration completely and hide this message, set AT4xMigrationTask::enable_v4_migration to false.', 'notice');
+
+            return;
+        }
+
         $versionedFields = array_keys(Config::inst()->get(Versioned::class, 'db_for_versions_table'));
         $termTableFields = DB::query(sprintf('SHOW COLUMNS FROM "%s"', $termTable))->column();
 
@@ -93,10 +102,23 @@ public function run($request)
                         if (get_parent_class($model) === DataObject::class) {
                             array_push($dbFields, ...$versionedFields);
                         } else {
-                            array_push($dbFields, 'RecordID', 'Version');
+                            array_push($dbFields, ...$this->basicFields);
                         }
                     }
 
+
+                    $currentTermTableFields = DB::query(sprintf('SHOW COLUMNS FROM "%s"', $termTable . $dbTableSuffix))->column();
+                    $dbFieldsDiff = array_intersect(array_unique($dbFields), $currentTermTableFields);
+
+                    // if there are no columns to migrate, i.e. if the only fields are the basic versioning related field
+                    // and an ID, skip the table for the current model
+                    if (empty($dbFieldsDiff) || empty(array_diff($dbFieldsDiff, $this->basicFields)) || ($dbFieldsDiff == ['ID'])) {
+                        DB::get_schema()->alterationMessage(sprintf('No column data to migrate to %s table.', $dbTable), 'notice');
+
+                        continue;
+                    }
+
+
                     DB::get_schema()->alterationMessage(sprintf('Migrating data to %s table.', $dbTable), 'changed');
 
                     // make sure the table is empty to avoid foreign key conflicts

From b41057d4e269de8e22ab4369500b280d3e5a4c0f Mon Sep 17 00:00:00 2001
From: Michal Kleiner <michal.kleiner@chrometoaster.com>
Date: Fri, 30 Apr 2021 00:37:10 +1200
Subject: [PATCH 2/2] Tweak wording of the DB alteration messages

---
 src/Dev/AT4xMigrationTask.php | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/Dev/AT4xMigrationTask.php b/src/Dev/AT4xMigrationTask.php
index 2857e33..874dd80 100644
--- a/src/Dev/AT4xMigrationTask.php
+++ b/src/Dev/AT4xMigrationTask.php
@@ -64,7 +64,7 @@ public function run($request)
         // Skip migration when BaseObject or BaseTerm have any data in them
         if ($baseObjectsCount || $baseTermsCount) {
             DB::get_schema()->alterationMessage("BaseObject or BaseTerm table already contains data, skipping the migration.", 'notice');
-            DB::get_schema()->alterationMessage('If you want disable the migration completely and hide this message, set AT4xMigrationTask::enable_v4_migration to false.', 'notice');
+            DB::get_schema()->alterationMessage('If you want to disable the migration completely and hide this message, set AT4xMigrationTask::enable_v4_migration to false.', 'notice');
 
             return;
         }
@@ -72,7 +72,7 @@ public function run($request)
         // Skip migration if there's no data at all
         if (($baseObjectsCount == $baseTermsCount) && ($baseObjectsCount == $termsCount) && ($baseObjectsCount == 0)) {
             DB::get_schema()->alterationMessage("There's no data to migrate, skipping the migration.", 'notice');
-            DB::get_schema()->alterationMessage('If you want disable the migration completely and hide this message, set AT4xMigrationTask::enable_v4_migration to false.', 'notice');
+            DB::get_schema()->alterationMessage('If you want to disable the migration completely, e.g. for fresh installs, set AT4xMigrationTask::enable_v4_migration to false.', 'notice');
 
             return;
         }