Resolved #557: Implement NullBackgroundJobManager.

framework/src/Volo.Abp.BackgroundJobs.Abstractions/Volo/Abp/BackgroundJobs/BackgroundJobManagerExtensions.cs

@@ -1,4 +1,5 @@
 using System;
+using Volo.Abp.DynamicProxy;
 using Volo.Abp.Threading;
 
 namespace Volo.Abp.BackgroundJobs
@@ -20,5 +21,16 @@ namespace Volo.Abp.BackgroundJobs
         {
             return AsyncHelper.RunSync(() => backgroundJobManager.EnqueueAsync<TArgs>(args, priority, delay));
         }
+
+        /// <summary>
+        /// Checks if background job system has a real implementation.
+        /// It returns false if the current implementation is <see cref="NullBackgroundJobManager"/>.
+        /// </summary>
+        /// <param name="backgroundJobManager"></param>
+        /// <returns></returns>
+        public static bool IsAvailable(this IBackgroundJobManager backgroundJobManager)
+        {
+            return !(ProxyHelper.UnProxy(backgroundJobManager) is NullBackgroundJobManager);
+        }
     }
 }

framework/src/Volo.Abp.BackgroundJobs.Abstractions/Volo/Abp/BackgroundJobs/NullBackgroundJobManager.cs

@@ -0,0 +1,25 @@
+using System;
+using System.Threading.Tasks;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Logging.Abstractions;
+using Volo.Abp.DependencyInjection;
+
+namespace Volo.Abp.BackgroundJobs
+{
+    [Dependency(TryRegister = true)]
+    public class NullBackgroundJobManager : IBackgroundJobManager, ISingletonDependency
+    {
+        public ILogger<NullBackgroundJobManager> Logger { get; set; }
+
+        public NullBackgroundJobManager()
+        {
+            Logger = NullLogger<NullBackgroundJobManager>.Instance;
+        }
+
+        public virtual Task<string> EnqueueAsync<TArgs>(TArgs args, BackgroundJobPriority priority = BackgroundJobPriority.Normal,
+            TimeSpan? delay = null)
+        {
+            throw new AbpException("Background job system has not a real implementation. If it's mandatory, use an implementation (either the default provider or a 3rd party implementation). If it's optional, check IBackgroundJobManager.IsAvailable() extension method and act based on it.");
+        }
+    }
+}

framework/src/Volo.Abp.BackgroundJobs.RabbitMQ/Volo/Abp/BackgroundJobs/RabbitMQ/RabbitMqBackgroundJobManager.cs

@@ -4,6 +4,7 @@ using Volo.Abp.DependencyInjection;
 
 namespace Volo.Abp.BackgroundJobs.RabbitMQ
 {
+    [Dependency(ReplaceServices = true)]
     public class RabbitMqBackgroundJobManager : IBackgroundJobManager, ITransientDependency
     {
         private readonly IJobQueueManager _jobQueueManager;

framework/src/Volo.Abp.BackgroundJobs/Volo/Abp/BackgroundJobs/BackgroundJobWorker.cs

@@ -17,9 +17,6 @@ namespace Volo.Abp.BackgroundJobs
         protected IClock Clock { get; }
         protected IBackgroundJobSerializer Serializer { get; }
 
-        /// <summary>
-        /// Initializes a new instance of the <see cref="DefaultBackgroundJobManager"/> class.
-        /// </summary>
         public BackgroundJobWorker(
             IBackgroundJobStore store,
             AbpTimer timer,

framework/src/Volo.Abp.BackgroundJobs/Volo/Abp/BackgroundJobs/DefaultBackgroundJobManager.cs

@@ -9,7 +9,7 @@ namespace Volo.Abp.BackgroundJobs
     /// <summary>
     /// Default implementation of <see cref="IBackgroundJobManager"/>.
     /// </summary>
-    [Dependency(TryRegister = true)]
+    [Dependency(ReplaceServices = true)]
     public class DefaultBackgroundJobManager : IBackgroundJobManager, ISingletonDependency
     {
         protected IClock Clock { get; }
@@ -17,9 +17,6 @@ namespace Volo.Abp.BackgroundJobs
         protected IGuidGenerator GuidGenerator { get; }
         protected IBackgroundJobStore Store { get; }
         
-        /// <summary>
-        /// Initializes a new instance of the <see cref="DefaultBackgroundJobManager"/> class.
-        /// </summary>
         public DefaultBackgroundJobManager(
             IClock clock,
             IBackgroundJobSerializer serializer,

framework/src/Volo.Abp.Emailing/Volo/Abp/Emailing/EmailSenderBase.cs

@@ -68,6 +68,12 @@ namespace Volo.Abp.Emailing
 
         public virtual async Task QueueAsync(string to, string subject, string body, bool isBodyHtml = true)
         {
+            if (!BackgroundJobManager.IsAvailable())
+            {
+                await SendAsync(to, subject, body, isBodyHtml);
+                return;
+            }
+
             await BackgroundJobManager.EnqueueAsync(
                 new BackgroundEmailSendingJobArgs
                 {