Introduce the IEventDataMayHaveTenantId interface.

framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Events/Distributed/EntityCreatedEto.cs

@@ -1,11 +1,12 @@
 using System;
 using Volo.Abp.EventBus;
+using Volo.Abp.MultiTenancy;
 
 namespace Volo.Abp.Domain.Entities.Events.Distributed
 {
     [Serializable]
     [GenericEventName(Postfix = ".Created")]
-    public class EntityCreatedEto<TEntityEto>
+    public class EntityCreatedEto<TEntityEto> : IEventDataMayHaveTenantId
     {
         public TEntityEto Entity { get; set; }
 
@@ -13,5 +14,17 @@ namespace Volo.Abp.Domain.Entities.Events.Distributed
         {
             Entity = entity;
         }
+
+        public virtual bool IsMultiTenant(out Guid? tenantId)
+        {
+            if (Entity is IMultiTenant multiTenantEntity)
+            {
+                tenantId = multiTenantEntity.TenantId;
+                return true;
+            }
+
+            tenantId = null;
+            return false;
+        }
     }
 }

framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Events/Distributed/EntityDeletedEto.cs

@@ -1,11 +1,12 @@
 using System;
 using Volo.Abp.EventBus;
+using Volo.Abp.MultiTenancy;
 
 namespace Volo.Abp.Domain.Entities.Events.Distributed
 {
     [Serializable]
     [GenericEventName(Postfix = ".Deleted")]
-    public class EntityDeletedEto<TEntityEto>
+    public class EntityDeletedEto<TEntityEto> : IEventDataMayHaveTenantId
     {
         public TEntityEto Entity { get; set; }
 
@@ -13,5 +14,17 @@ namespace Volo.Abp.Domain.Entities.Events.Distributed
         {
             Entity = entity;
         }
+
+        public virtual bool IsMultiTenant(out Guid? tenantId)
+        {
+            if (Entity is IMultiTenant multiTenantEntity)
+            {
+                tenantId = multiTenantEntity.TenantId;
+                return true;
+            }
+
+            tenantId = null;
+            return false;
+        }
     }
-}
+}

framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Events/Distributed/EntityUpdatedEto.cs

@@ -1,11 +1,12 @@
 using System;
 using Volo.Abp.EventBus;
+using Volo.Abp.MultiTenancy;
 
 namespace Volo.Abp.Domain.Entities.Events.Distributed
 {
     [Serializable]
     [GenericEventName(Postfix = ".Updated")]
-    public class EntityUpdatedEto<TEntityEto>
+    public class EntityUpdatedEto<TEntityEto> : IEventDataMayHaveTenantId
     {
         public TEntityEto Entity { get; set; }
 
@@ -13,5 +14,17 @@ namespace Volo.Abp.Domain.Entities.Events.Distributed
         {
             Entity = entity;
         }
+
+        public virtual bool IsMultiTenant(out Guid? tenantId)
+        {
+            if (Entity is IMultiTenant multiTenantEntity)
+            {
+                tenantId = multiTenantEntity.TenantId;
+                return true;
+            }
+
+            tenantId = null;
+            return false;
+        }
     }
-}
+}

framework/src/Volo.Abp.Ddd.Domain/Volo/Abp/Domain/Entities/Events/EntityEventData.cs

@@ -1,5 +1,6 @@
 using System;
 using Volo.Abp.EventBus;
+using Volo.Abp.MultiTenancy;
 
 namespace Volo.Abp.Domain.Entities.Events
 {
@@ -8,7 +9,7 @@ namespace Volo.Abp.Domain.Entities.Events
     /// </summary>
     /// <typeparam name="TEntity">Entity type</typeparam>
     [Serializable]
-    public class EntityEventData<TEntity> : IEventDataWithInheritableGenericArgument
+    public class EntityEventData<TEntity> : IEventDataWithInheritableGenericArgument, IEventDataMayHaveTenantId
     {
         /// <summary>
         /// Related entity with this event.
@@ -28,5 +29,17 @@ namespace Volo.Abp.Domain.Entities.Events
         {
             return new object[] { Entity };
         }
+
+        public virtual bool IsMultiTenant(out Guid? tenantId)
+        {
+            if (Entity is IMultiTenant multiTenantEntity)
+            {
+                tenantId = multiTenantEntity.TenantId;
+                return true;
+            }
+
+            tenantId = null;
+            return false;
+        }
     }
-}
+}

framework/src/Volo.Abp.EventBus/Volo/Abp/EventBus/IEventDataMayHaveTenantId.cs

@@ -0,0 +1,28 @@
+using System;
+
+namespace Volo.Abp.EventBus
+{
+    /// <summary>
+    /// An event data object (or event transfer object) can implement this interface
+    /// to indicate that this event may be related to a tenant.
+    ///
+    /// If an event data class is always related to a tenant, then directly implement the
+    /// <see cref="IsMultiTenant"/> interface instead of this one.
+    ///
+    /// This interface is typically implemented by generic event handlers where the generic
+    /// parameter may implement <see cref="IsMultiTenant"/> or not.
+    /// </summary>
+    public interface IEventDataMayHaveTenantId
+    {
+        /// <summary>
+        /// Returns true if this event data has a Tenant Id information.
+        /// If so, it should set the <see cref="tenantId"/> our parameter.
+        /// Otherwise, the <see cref="tenantId"/> our parameter value should not be informative
+        /// (it will be null as expected, but doesn't indicate a tenant with null tenant id).
+        /// </summary>
+        /// <param name="tenantId">
+        /// The tenant id that is set if this method returns true.
+        /// </param>
+        bool IsMultiTenant(out Guid? tenantId);
+    }
+}