From dfed93a4ab1da5689bb11784841d93315a13034b Mon Sep 17 00:00:00 2001
From: Shannon <sdeminick@gmail.com>
Date: Wed, 14 Aug 2019 14:49:05 +1000
Subject: [PATCH] Fixes dropping unique constraint indexes and oddly named FKs

---
 .../DeleteKeysAndIndexesBuilder.cs            | 44 +++++++++++++++----
 1 file changed, 36 insertions(+), 8 deletions(-)

diff --git a/src/Umbraco.Core/Migrations/Expressions/Delete/KeysAndIndexes/DeleteKeysAndIndexesBuilder.cs b/src/Umbraco.Core/Migrations/Expressions/Delete/KeysAndIndexes/DeleteKeysAndIndexesBuilder.cs
index 9b13457b76..df74bf7c87 100644
--- a/src/Umbraco.Core/Migrations/Expressions/Delete/KeysAndIndexes/DeleteKeysAndIndexesBuilder.cs
+++ b/src/Umbraco.Core/Migrations/Expressions/Delete/KeysAndIndexes/DeleteKeysAndIndexesBuilder.cs
@@ -1,5 +1,7 @@
-using System.Linq;
+using System.Collections.Generic;
+using System.Linq;
 using NPoco;
+using Umbraco.Core;
 using Umbraco.Core.Migrations.Expressions.Common;
 using Umbraco.Core.Persistence.SqlSyntax;
 
@@ -27,31 +29,57 @@ namespace Umbraco.Core.Migrations.Expressions.Delete.KeysAndIndexes
         {
             _context.BuildingExpression = false;
 
+            //get a list of all constraints - this will include all PK, FK and unique constraints
+            var tableConstraints = _context.SqlContext.SqlSyntax.GetConstraintsPerTable(_context.Database).DistinctBy(x => x.Item2).ToList();
+
+            //get a list of defined indexes - this will include all indexes, unique indexes and unique constraint indexes
+            var indexes = _context.SqlContext.SqlSyntax.GetDefinedIndexesDefinitions(_context.Database).DistinctBy(x => x.IndexName).ToList();
+
+            var uniqueConstraintNames = tableConstraints.Where(x => !x.Item2.InvariantStartsWith("PK_") && !x.Item2.InvariantStartsWith("FK_")).Select(x => x.Item2);
+            var indexNames = indexes.Select(x => x.IndexName).ToList();
+
             // drop keys
             if (DeleteLocal || DeleteForeign)
             {
                 // table, constraint
-                var tableKeys = _context.SqlContext.SqlSyntax.GetConstraintsPerTable(_context.Database).DistinctBy(x => x.Item2).ToList();
+                
                 if (DeleteForeign)
                 {
-                    foreach (var key in tableKeys.Where(x => x.Item1 == TableName && x.Item2.StartsWith("FK_")))
+                    //In some cases not all FK's are prefixed with "FK" :/ mostly with old upgraded databases so we need to check if it's either:
+                    // * starts with FK OR
+                    // * doesn't start with PK_ and doesn't exist in the list of indexes
+
+                    foreach (var key in tableConstraints.Where(x => x.Item1 == TableName
+                        && (x.Item2.InvariantStartsWith("FK_") || (!x.Item2.InvariantStartsWith("PK_") && !indexNames.InvariantContains(x.Item2)))))
+                    {
                         Delete.ForeignKey(key.Item2).OnTable(key.Item1).Do();
+                    }
+                        
                 }
                 if (DeleteLocal)
                 {
-                    foreach (var key in tableKeys.Where(x => x.Item1 == TableName && x.Item2.StartsWith("PK_")))
+                    foreach (var key in tableConstraints.Where(x => x.Item1 == TableName && x.Item2.InvariantStartsWith("PK_")))
                         Delete.PrimaryKey(key.Item2).FromTable(key.Item1).Do();
 
-                    // note: we do *not* delete the DEFAULT constraints
+                    // note: we do *not* delete the DEFAULT constraints and if we wanted to we'd have to deal with that in interesting ways
+                    // since SQL server has a specific way to handle that, see SqlServerSyntaxProvider.GetDefaultConstraintsPerColumn
                 }
             }
 
             // drop indexes
             if (DeleteLocal)
-            {
-                var indexes = _context.SqlContext.SqlSyntax.GetDefinedIndexesDefinitions(_context.Database).DistinctBy(x => x.IndexName).ToList();
+            {   
                 foreach (var index in indexes.Where(x => x.TableName == TableName))
-                    Delete.Index(index.IndexName).OnTable(index.TableName).Do();
+                {
+                    //if this is a unique constraint we need to drop the constraint, else drop the index
+                    //to figure this out, the index must be tagged as unique and it must exist in the tableConstraints
+
+                    if (index.IsUnique && uniqueConstraintNames.InvariantContains(index.IndexName))
+                        Delete.UniqueConstraint(index.IndexName).FromTable(index.TableName).Do();
+                    else
+                        Delete.Index(index.IndexName).OnTable(index.TableName).Do();
+                }
+                    
             }
         }