From f8e8774d8cf0e626b7ee1cacab8d39ac602af497 Mon Sep 17 00:00:00 2001
From: Robert Marshall <rob@robware.uk>
Date: Wed, 15 Jul 2020 18:32:38 +0100
Subject: [PATCH] Find the latest ID to set the new ID against instead of
 assuming count is good

---
 src/Robware.Data.Tests/BlogRepositoryTests.cs |  7 ++++++-
 src/Robware.Data/BlogRepository.cs            | 12 +++++++++++-
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/src/Robware.Data.Tests/BlogRepositoryTests.cs b/src/Robware.Data.Tests/BlogRepositoryTests.cs
index b928982..cea8120 100644
--- a/src/Robware.Data.Tests/BlogRepositoryTests.cs
+++ b/src/Robware.Data.Tests/BlogRepositoryTests.cs
@@ -4,6 +4,7 @@ using NSubstitute;
 using Robware.Blog;
 using Robware.Blog.Data.State;
 using System;
+using System.Threading;
 using System.Threading.Tasks;
 using Xunit;
 
@@ -11,8 +12,12 @@ namespace Robware.Data.Tests {
 	public class BlogRepositoryTests {
 		[Fact]
 		public async Task SavePost_WithNewPost_GetsNewIdAndSetsTimestampAndSavesAsync() {
+			var findResult = Substitute.For<IAsyncCursor<BlogPostState>>();
+			findResult.Current.Returns(new[] { new BlogPostState { Id = 10 } });
+			findResult.MoveNext(Arg.Any<CancellationToken>()).Returns(true, false);
+			findResult.MoveNextAsync(Arg.Any<CancellationToken>()).Returns(true, false);
 			var collection = Substitute.For<IMongoCollection<BlogPostState>>();
-			collection.CountDocumentsAsync(Arg.Any<FilterDefinition<BlogPostState>>()).Returns(10);
+			collection.FindAsync(Arg.Any<FilterDefinition<BlogPostState>>(), Arg.Any<FindOptions<BlogPostState>>()).Returns(findResult);
 			var database = Substitute.For<IMongoDatabase>();
 			database.GetCollection<BlogPostState>("blog").Returns(collection);
 
diff --git a/src/Robware.Data/BlogRepository.cs b/src/Robware.Data/BlogRepository.cs
index 5696a20..00cb597 100644
--- a/src/Robware.Data/BlogRepository.cs
+++ b/src/Robware.Data/BlogRepository.cs
@@ -67,9 +67,19 @@ namespace Robware.Data {
 
 		public async Task<BlogPost> GetPostByUrlAsync(string url) => await GetPostAsync(post => post.Url == url && !post.Deleted);
 
+		private async Task<int> GetLastPostId() {
+			var sort = Builders<BlogPostState>.Sort.Descending(post => post.Id);
+			var options = new FindOptions<BlogPostState> {
+				Sort = sort,
+				Limit = 1
+			};
+			var states = (await _collection.FindAsync<BlogPostState>(_ => true, options)).ToEnumerable();
+			return states.First().Id;
+		}
+
 		public async Task<BlogPost> SavePost(BlogPost post) {
 			if (post.Id == 0) {
-				post.Id = (await GetCountAsync(true)) + 1;
+				post.Id = (await GetLastPostId()) + 1;
 				post.Timestamp = DateTime.Now;
 			}