Fix issue when underlying index of ForeignKey tries to be removed without FK itself

in MySQL it causes issues

Author: alex-kulakov

Orm/Xtensive.Orm/Orm/Upgrade/Internals/SqlActionTranslator.cs

@@ -45,6 +45,7 @@ internal sealed class SqlActionTranslator
     private readonly List<string> enforceChangedColumns = new List<string>();
     private readonly ISqlExecutor sqlExecutor;
     private readonly bool allowCreateConstraints;
+    private readonly bool removeFkBeforeIndex;
 
     private readonly string collationName;
     private readonly ActionSequence actions;
@@ -60,6 +61,7 @@ internal sealed class SqlActionTranslator
     private readonly List<DataAction> clearDataActions = new List<DataAction>();
     private readonly HashSet<TableColumn> recreatedColumns = new HashSet<TableColumn>();
     private readonly Dictionary<string, SequenceDescriptor> removedGeneratorDescriptors = new Dictionary<string, SequenceDescriptor>();
+    private readonly List<(Table, string)> removedForeignKeysDueToIndexes = new List<(Table, string)>();
 
 
     private UpgradeActionSequenceBuilder currentOutput;
@@ -563,8 +565,16 @@ private void VisitRemoveSecondaryIndexAction(RemoveNodeAction action)
         return;
 
       var index = table.Indexes[secondaryIndexInfo.Name];
+      if (removeFkBeforeIndex && secondaryIndexInfo.Parent.ForeignKeys.TryGetValue(secondaryIndexInfo.Name, out var dependantFk)) {
+        var foreignKey = table.TableConstraints[dependantFk.Name];
+        if (foreignKey != null) {
+          removedForeignKeysDueToIndexes.Add((table, foreignKey.Name));
+          preCleanupDataOutput.RegisterCommand(SqlDdl.Alter(table, SqlDdl.DropConstraint(foreignKey)));
+          _ = table.TableConstraints.Remove(foreignKey);
+        }
+      }
       preCleanupDataOutput.RegisterCommand(SqlDdl.Drop(index));
-      table.Indexes.Remove(index);
+      _ = table.Indexes.Remove(index);
     }
 
     private void VisitAlterSecondaryIndexAction(NodeAction action)
@@ -595,9 +605,14 @@ private void VisitRemoveForeignKeyAction(RemoveNodeAction action)
       if (table==null)
         return;
 
+      if (removeFkBeforeIndex && removedForeignKeysDueToIndexes.Contains((table, foreignKeyInfo.Name))) {
+        // index removal already causes FK removal
+        return;
+      }
+
       var foreignKey = table.TableConstraints[foreignKeyInfo.Name];
       preCleanupDataOutput.RegisterCommand(SqlDdl.Alter(table, SqlDdl.DropConstraint(foreignKey)));
-      table.TableConstraints.Remove(foreignKey);
+      _ = table.TableConstraints.Remove(foreignKey);
     }
 
     private void VisitAlterForeignKeyAction(NodeAction action)
@@ -1270,7 +1285,6 @@ public SqlActionTranslator(
       driver = handlers.StorageDriver;
       providerInfo = handlers.ProviderInfo;
       sequenceQueryBuilder = handlers.SequenceQueryBuilder;
-      providerInfo = handlers.ProviderInfo;
       typeIdColumnName = handlers.NameBuilder.TypeIdColumnName;
 
       this.resolver = resolver;
@@ -1287,6 +1301,9 @@ public SqlActionTranslator(
         if (!string.IsNullOrEmpty(collation))
           collationName = collation;
       }
+      if (providerInfo.ProviderName == WellKnown.Provider.MySql) {
+        removeFkBeforeIndex = true;
+      }
     }
   }
 }