Add MongoDB transactions to WordRepository multi-collection operations (#4191)

Author: Copilot

Backend.Tests/Mocks/MongoDbContextMock.cs

@@ -15,6 +15,8 @@ public Task<IMongoTransaction> BeginTransaction()
 
     private sealed class MongoTransactionMock : IMongoTransaction
     {
+        public IClientSessionHandle Session => null!;
+
         public Task CommitTransactionAsync()
         {
             return Task.CompletedTask;

Backend/Contexts/MongoDbContext.cs

@@ -26,6 +26,8 @@ private class MongoTransactionWrapper(IClientSessionHandle session) : IMongoTran
     {
         private readonly IClientSessionHandle _session = session;
 
+        public IClientSessionHandle Session => _session;
+
         public Task CommitTransactionAsync()
         {
             return _session.CommitTransactionAsync();

Backend/Interfaces/IMongoDbContext.cs

@@ -12,6 +12,7 @@ public interface IMongoDbContext
 
 public interface IMongoTransaction : IDisposable
 {
+    IClientSessionHandle Session { get; }
     Task CommitTransactionAsync();
     Task AbortTransactionAsync();
 }

Backend/Repositories/WordRepository.cs

@@ -15,6 +15,7 @@ namespace BackendFramework.Repositories
     [ExcludeFromCodeCoverage]
     public class WordRepository(IMongoDbContext dbContext) : IWordRepository
     {
+        private readonly IMongoDbContext _dbContext = dbContext;
         private readonly IMongoCollection<Word> _frontier = dbContext.Db.GetCollection<Word>("FrontierCollection");
         private readonly IMongoCollection<Word> _words = dbContext.Db.GetCollection<Word>("WordsCollection");
 
@@ -100,9 +101,19 @@ public async Task<bool> DeleteAllWords(string projectId)
             var filterDef = new FilterDefinitionBuilder<Word>();
             var filter = filterDef.Eq(x => x.ProjectId, projectId);
 
-            var deleted = await _words.DeleteManyAsync(filter);
-            await _frontier.DeleteManyAsync(filter);
-            return deleted.DeletedCount != 0;
+            using var transaction = await _dbContext.BeginTransaction();
+            try
+            {
+                var deleted = await _words.DeleteManyAsync(transaction.Session, filter);
+                await _frontier.DeleteManyAsync(transaction.Session, filter);
+                await transaction.CommitTransactionAsync();
+                return deleted.DeletedCount != 0;
+            }
+            catch
+            {
+                await transaction.AbortTransactionAsync();
+                throw;
+            }
         }
 
         /// <summary> Removes all <see cref="Word"/>s from the Frontier for specified <see cref="Project"/> </summary>
@@ -146,8 +157,18 @@ public async Task<Word> Create(Word word)
                 OtelService.StartActivityWithTag(otelTagName, "creating a word in WordsCollection and Frontier");
 
             PopulateBlankWordTimes(word);
-            await _words.InsertOneAsync(word);
-            await AddFrontier(word);
+            using var transaction = await _dbContext.BeginTransaction();
+            try
+            {
+                await _words.InsertOneAsync(transaction.Session, word);
+                await _frontier.InsertOneAsync(transaction.Session, word);
+                await transaction.CommitTransactionAsync();
+            }
+            catch
+            {
+                await transaction.AbortTransactionAsync();
+                throw;
+            }
             return word;
         }
 
@@ -170,8 +191,18 @@ public async Task<List<Word>> Create(List<Word> words)
             {
                 PopulateBlankWordTimes(w);
             }
-            await _words.InsertManyAsync(words);
-            await AddFrontier(words);
+            using var transaction = await _dbContext.BeginTransaction();
+            try
+            {
+                await _words.InsertManyAsync(transaction.Session, words);
+                await _frontier.InsertManyAsync(transaction.Session, words);
+                await transaction.CommitTransactionAsync();
+            }
+            catch
+            {
+                await transaction.AbortTransactionAsync();
+                throw;
+            }
             return words;
         }
 
@@ -204,9 +235,20 @@ public async Task<Word> CreateAndDeleteFrontier(Word newWord, string oldWordId)
                 otelTagName, "creating word in WordsCollection and Frontier, deleting old word from Frontier");
 
             PopulateBlankWordTimes(newWord);
-            await _words.InsertOneAsync(newWord);
-            await _frontier.InsertOneAsync(newWord);
-            await _frontier.FindOneAndDeleteAsync(GetProjectWordFilter(newWord.ProjectId, oldWordId));
+            using var transaction = await _dbContext.BeginTransaction();
+            try
+            {
+                await _words.InsertOneAsync(transaction.Session, newWord);
+                await _frontier.InsertOneAsync(transaction.Session, newWord);
+                await _frontier.FindOneAndDeleteAsync(
+                    transaction.Session, GetProjectWordFilter(newWord.ProjectId, oldWordId));
+                await transaction.CommitTransactionAsync();
+            }
+            catch
+            {
+                await transaction.AbortTransactionAsync();
+                throw;
+            }
             return newWord;
         }
 
@@ -224,8 +266,19 @@ public async Task<Word> AddAndDeleteFrontier(Word deletedWord, string wordId)
                 otelTagName, "adding word to WordsCollection, deleting word from Frontier");
 
             PopulateBlankWordTimes(deletedWord);
-            await _words.InsertOneAsync(deletedWord);
-            await _frontier.FindOneAndDeleteAsync(GetProjectWordFilter(deletedWord.ProjectId, wordId));
+            using var transaction = await _dbContext.BeginTransaction();
+            try
+            {
+                await _words.InsertOneAsync(transaction.Session, deletedWord);
+                await _frontier.FindOneAndDeleteAsync(
+                    transaction.Session, GetProjectWordFilter(deletedWord.ProjectId, wordId));
+                await transaction.CommitTransactionAsync();
+            }
+            catch
+            {
+                await transaction.AbortTransactionAsync();
+                throw;
+            }
             return deletedWord;
         }