Add transactions to the MongoDbContext

Author: imnasnainaec

Backend.Tests/Mocks/MongoDbContextMock.cs

@@ -0,0 +1,32 @@
+using System;
+using System.Threading.Tasks;
+using BackendFramework.Interfaces;
+using MongoDB.Driver;
+
+namespace Backend.Tests.Mocks;
+
+public class MongoDbContextMock : IMongoDbContext
+{
+    public IMongoDatabase Db => throw new NotSupportedException();
+    public Task<IMongoTransaction> BeginTransaction()
+    {
+        return Task.FromResult<IMongoTransaction>(new MongoTransactionMock());
+    }
+
+    private sealed class MongoTransactionMock : IMongoTransaction
+    {
+        public Task CommitTransactionAsync()
+        {
+            return Task.CompletedTask;
+        }
+
+        public Task AbortTransactionAsync()
+        {
+            return Task.CompletedTask;
+        }
+
+        public void Dispose()
+        {
+        }
+    }
+}

Backend/Contexts/MongoDbContext.cs

@@ -1,28 +1,44 @@
-using System;
-using System.Diagnostics.CodeAnalysis;
+using System.Threading.Tasks;
 using BackendFramework.Interfaces;
 using Microsoft.Extensions.Options;
 using MongoDB.Driver;
 
-namespace BackendFramework.Contexts
+namespace BackendFramework.Contexts;
+
+public class MongoDbContext : IMongoDbContext
 {
-    [ExcludeFromCodeCoverage]
-    public class MongoDbContext : IMongoDbContext
+    public IMongoDatabase Db { get; }
+
+    public MongoDbContext(IOptions<Startup.Settings> options)
+    {
+        var client = new MongoClient(options.Value.ConnectionString);
+        Db = client.GetDatabase(options.Value.CombineDatabase);
+    }
+
+    public async Task<IMongoTransaction> BeginTransaction()
     {
-        private MongoClient _mongoClient { get; }
+        var session = await Db.Client.StartSessionAsync();
+        session.StartTransaction();
+        return new MongoTransactionWrapper(session);
+    }
+
+    private class MongoTransactionWrapper(IClientSessionHandle session) : IMongoTransaction
+    {
+        private readonly IClientSessionHandle _session = session;
 
-        public IMongoDatabase Db { get; }
+        public Task CommitTransactionAsync()
+        {
+            return _session.CommitTransactionAsync();
+        }
 
-        public MongoDbContext(IOptions<Startup.Settings> options)
+        public Task AbortTransactionAsync()
         {
-            _mongoClient = new MongoClient(options.Value.ConnectionString);
-            Db = _mongoClient.GetDatabase(options.Value.CombineDatabase);
+            return _session.AbortTransactionAsync();
         }
 
         public void Dispose()
         {
-            _mongoClient.Dispose();
-            GC.SuppressFinalize(this);
+            _session.Dispose();
         }
     }
 }

Backend/Interfaces/IMongoDbContext.cs

@@ -1,10 +1,17 @@
 using System;
+using System.Threading.Tasks;
 using MongoDB.Driver;
 
-namespace BackendFramework.Interfaces
+namespace BackendFramework.Interfaces;
+
+public interface IMongoDbContext
+{
+    IMongoDatabase Db { get; }
+    Task<IMongoTransaction> BeginTransaction();
+}
+
+public interface IMongoTransaction : IDisposable
 {
-    public interface IMongoDbContext : IDisposable
-    {
-        IMongoDatabase Db { get; }
-    }
+    Task CommitTransactionAsync();
+    Task AbortTransactionAsync();
 }

Backend/Startup.cs

@@ -350,7 +350,8 @@ public void Configure(IApplicationBuilder app, IWebHostEnvironment env, IHostApp
 
             // If an admin user has been created via the command line, treat that as a single action and shut the
             // server down so the calling script knows it's been completed successfully or unsuccessfully.
-            var userRepo = app.ApplicationServices.GetService<IUserRepository>();
+            using var startupScope = app.ApplicationServices.CreateAsyncScope();
+            var userRepo = startupScope.ServiceProvider.GetService<IUserRepository>();
             if (userRepo is not null && CreateAdminUser(userRepo))
             {
                 _logger.LogInformation("Stopping application");