Fixes #7798 : Invalid implementation of IEnumerable in Content Cache

src/Umbraco.Tests/PublishedContent/NuCacheChildrenTests.cs

@@ -1,9 +1,7 @@
 using System;
-using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Data;
 using System.Linq;
-using System.Reflection;
 using Moq;
 using NUnit.Framework;
 using Umbraco.Core;
@@ -27,7 +25,6 @@ using Umbraco.Web.Cache;
 using Umbraco.Web.PublishedCache;
 using Umbraco.Web.PublishedCache.NuCache;
 using Umbraco.Web.PublishedCache.NuCache.DataSource;
-using Umbraco.Web.PublishedCache.NuCache.Snap;
 
 namespace Umbraco.Tests.PublishedContent
 {
@@ -1312,6 +1309,18 @@ namespace Umbraco.Tests.PublishedContent
             AssertLinkedNode(child3.contentNode, 1, 3, -1, -1, -1);
         }
 
+        [Test]
+        public void MultipleCacheIteration()
+        {
+            //see https://github.com/umbraco/Umbraco-CMS/issues/7798
+            this.Init(this.GetInvariantKits());
+            var snapshot = this._snapshotService.CreatePublishedSnapshot(previewToken: null);
+            this._snapshotAccessor.PublishedSnapshot = snapshot;
+
+            var items = snapshot.Content.GetByXPath("/root/itype");
+            Assert.AreEqual(items.Count(), items.Count());
+        }
+
         private void AssertLinkedNode(ContentNode node, int parent, int prevSibling, int nextSibling, int firstChild, int lastChild)
         {
             Assert.AreEqual(parent, node.ParentContentId);

src/Umbraco.Web/PublishedCache/NuCache/ContentCache.cs

@@ -355,6 +355,7 @@ namespace Umbraco.Web.PublishedCache.NuCache
 
         private static IEnumerable<IPublishedContent> GetByXPath(XPathNodeIterator iterator)
         {
+            iterator = iterator.Clone();
             while (iterator.MoveNext())
             {
                 var xnav = iterator.Current as NavigableNavigator;