Fix Multitenancy Support and Normalize Tenant ID Handling

Elsa.sln

@@ -196,12 +196,14 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "adr", "adr", "{0A04B1FD-06C
 		doc\adr\0001-record-architecture-decisions.md = doc\adr\0001-record-architecture-decisions.md
 		doc\adr\0002-fault-propagation-from-child-to-parent-activities.md = doc\adr\0002-fault-propagation-from-child-to-parent-activities.md
 		doc\adr\0003-direct-bookmark-management-in-workflowexecutioncontext.md = doc\adr\0003-direct-bookmark-management-in-workflowexecutioncontext.md
-		doc\adr\0004-token-centric-flowchart-execution-model.md = doc\adr\0004-token-centric-flowchart-execution-model.md
 		doc\adr\graph.dot = doc\adr\graph.dot
 		doc\adr\toc.md = doc\adr\toc.md
 		doc\adr\0005-activity-execution-snapshots.md = doc\adr\0004-activity-execution-snapshots.md
-		doc\adr\0006-tenant-deleted-event.md = doc\adr\0005-tenant-deleted-event.md
-		doc\adr\0006-adoption-of-explicit-merge-modes-for-flowchart-joins.md = doc\adr\0006-adoption-of-explicit-merge-modes-for-flowchart-joins.md
+		doc\adr\0005-tenant-deleted-event.md = doc\adr\0005-tenant-deleted-event.md
+		doc\adr\0005-token-centric-flowchart-execution-model.md = doc\adr\0005-token-centric-flowchart-execution-model.md
+		doc\adr\0006-tenant-deleted-event.md = doc\adr\0006-tenant-deleted-event.md
+		doc\adr\0007-adoption-of-explicit-merge-modes-for-flowchart-joins.md = doc\adr\0007-adoption-of-explicit-merge-modes-for-flowchart-joins.md
+		doc\adr\0008-empty-string-as-default-tenant-id.md = doc\adr\0008-empty-string-as-default-tenant-id.md
 	EndProjectSection
 EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "bounty", "bounty", "{9B80A705-2E31-4012-964A-83963DCDB384}"
@@ -327,6 +329,8 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Elsa.Resilience.Core.UnitTe
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Elsa.Common.UnitTests", "test\unit\Elsa.Common.UnitTests\Elsa.Common.UnitTests.csproj", "{A3C07D5B-2A30-494E-B9BC-4B1594B31ABC}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Elsa.Tenants.UnitTests", "test\unit\Elsa.Tenants.UnitTests\Elsa.Tenants.UnitTests.csproj", "{DC476900-D836-4920-A696-CF8796668723}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -591,6 +595,10 @@ Global
 		{A3C07D5B-2A30-494E-B9BC-4B1594B31ABC}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{A3C07D5B-2A30-494E-B9BC-4B1594B31ABC}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{A3C07D5B-2A30-494E-B9BC-4B1594B31ABC}.Release|Any CPU.Build.0 = Release|Any CPU
+		{DC476900-D836-4920-A696-CF8796668723}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{DC476900-D836-4920-A696-CF8796668723}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{DC476900-D836-4920-A696-CF8796668723}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{DC476900-D836-4920-A696-CF8796668723}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -694,6 +702,7 @@ Global
 		{874F5A44-DB06-47AB-A18C-2D13942E0147} = {477C2416-312D-46AE-BCD6-8FA1FAB43624}
 		{B8006D70-1630-43DB-A043-FA89FAC70F37} = {18453B51-25EB-4317-A4B3-B10518252E92}
 		{A3C07D5B-2A30-494E-B9BC-4B1594B31ABC} = {18453B51-25EB-4317-A4B3-B10518252E92}
+		{DC476900-D836-4920-A696-CF8796668723} = {18453B51-25EB-4317-A4B3-B10518252E92}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {D4B5CEAA-7D70-4FCB-A68E-B03FBE5E0E5E}

doc/adr/0004-token-centric-flowchart-execution-model.md → doc/adr/0005-token-centric-flowchart-execution-model.md

@@ -1,4 +1,4 @@
-# 4. Token-Centric Flowchart Execution Model
+# 5. Token-Centric Flowchart Execution Model
 
 Date: 2025-05-06
 

doc/adr/0005-tenant-deleted-event.md → doc/adr/0006-tenant-deleted-event.md

@@ -1,4 +1,4 @@
-# 5. Tenant Deleted Event
+# 6. Tenant Deleted Event
 
 Date: 2025-08-05
 

doc/adr/0006-adoption-of-explicit-merge-modes-for-flowchart-joins.md → doc/adr/0007-adoption-of-explicit-merge-modes-for-flowchart-joins.md

@@ -1,4 +1,4 @@
-# 6. Adoption of Explicit Merge Modes for Flowchart Joins
+# 7. Adoption of Explicit Merge Modes for Flowchart Joins
 
 Date: 2025-09-30
 

doc/adr/0008-empty-string-as-default-tenant-id.md

@@ -0,0 +1,48 @@
+# 8. Empty String as Default Tenant ID
+
+Date: 2026-01-27
+
+## Status
+
+Accepted
+
+## Context
+
+The multitenancy system in Elsa supports an optional mode where, when multitenancy is disabled, the system assumes a single tenant. When enabled, there's still a default tenant involved. The convention has been to use `null` as the tenant ID for the default tenant.
+
+However, this convention created several issues:
+
+1. **Dictionary compatibility**: The `DefaultTenantResolverPipelineInvoker` attempts to build a dictionary of tenants by their ID using `ToDictionary(x => x.Id)`, which throws an exception because dictionaries do not support null keys.
+2. **Inconsistency**: The codebase used `null`, empty string (`""`), and string literal `"default"` interchangeably to refer to the default tenant across different parts of the system (e.g., in configuration files and database records).
+3. **Code clarity**: Using `null` as a sentinel value for "default" is implicit and can be unclear to developers reading the code.
+
+## Decision
+
+We will standardize on using an **empty string** (`""`) as the tenant ID for the default tenant instead of `null`. This decision includes:
+
+1. **Define a constant**: Add `Tenant.DefaultTenantId = ""` to explicitly document the convention.
+2. **Update Tenant.Default**: Change `Tenant.Default.Id` from `null!` to use the `DefaultTenantId` constant.
+3. **Add normalization helper**: Create a `NormalizeTenantId()` extension method that converts `null` to empty string, ensuring backwards compatibility with code that still uses null.
+4. **Apply normalization consistently**: Use the normalization method in:
+   - Dictionary creation in `DefaultTenantResolverPipelineInvoker`
+   - Tenant lookups in `TenantResolverContext`
+   - Any other places where tenant IDs are compared or used as dictionary keys
+
+## Consequences
+
+### Positive
+
+- **No more exceptions**: Empty string is a valid dictionary key, eliminating the runtime exception in `DefaultTenantResolverPipelineInvoker`.
+- **Backwards compatible**: The `NormalizeTenantId()` extension method ensures that existing code using `null` or empty string will work correctly.
+- **Explicit convention**: The `DefaultTenantId` constant makes the convention clear and self-documenting.
+- **Simplified logic**: Reduces the need for null-checking throughout the multitenancy code.
+- **Consistency**: Aligns with parts of the codebase that were already using empty string (e.g., in configuration files).
+
+### Negative
+
+- **Migration consideration**: Existing data stores that have `null` tenant IDs will need to be normalized to empty strings, though the normalization helper provides a runtime solution.
+- **String vs null semantics**: Some developers may find using empty string less intuitive than null for representing "no tenant", though this is mitigated by the explicit constant.
+
+### Neutral
+
+- The empty string convention is common in multitenancy systems and aligns with string-based identifier patterns used elsewhere in the codebase.

doc/adr/graph.dot

@@ -8,7 +8,13 @@ _3 [label="3. Direct Bookmark Management in WorkflowExecutionContext"; URL="0003
 _2 -> _3 [style="dotted", weight=1];
 _4 [label="4. Activity Execution Snapshots"; URL="0004-activity-execution-snapshots.html"];
 _3 -> _4 [style="dotted", weight=1];
-_5 [label="5. Tenant Deleted Event"; URL="0005-tenant-deleted-event.html"];
+_5 [label="5. Token-Centric Flowchart Execution Model"; URL="0005-token-centric-flowchart-execution-model.html"];
 _4 -> _5 [style="dotted", weight=1];
+_6 [label="6. Tenant Deleted Event"; URL="0006-tenant-deleted-event.html"];
+_5 -> _6 [style="dotted", weight=1];
+_7 [label="7. Adoption of Explicit Merge Modes for Flowchart Joins"; URL="0007-adoption-of-explicit-merge-modes-for-flowchart-joins.html"];
+_6 -> _7 [style="dotted", weight=1];
+_8 [label="8. Empty String as Default Tenant ID"; URL="0008-empty-string-as-default-tenant-id.html"];
+_7 -> _8 [style="dotted", weight=1];
 }
 }

doc/adr/toc.md

@@ -4,4 +4,7 @@
 * [2. Fault Propagation from Child to Parent Activities](0002-fault-propagation-from-child-to-parent-activities.md)
 * [3. Direct Bookmark Management in WorkflowExecutionContext](0003-direct-bookmark-management-in-workflowexecutioncontext.md)
 * [4. Activity Execution Snapshots](0004-activity-execution-snapshots.md)
-* [5. Tenant Deleted Event](0005-tenant-deleted-event.md)
+* [5. Token-Centric Flowchart Execution Model](0005-token-centric-flowchart-execution-model.md)
+* [6. Tenant Deleted Event](0006-tenant-deleted-event.md)
+* [7. Adoption of Explicit Merge Modes for Flowchart Joins](0007-adoption-of-explicit-merge-modes-for-flowchart-joins.md)
+* [8. Empty String as Default Tenant ID](0008-empty-string-as-default-tenant-id.md)

src/apps/Elsa.Server.Web/Program.cs

@@ -4,12 +4,14 @@
 using Elsa.Expressions.Helpers;
 using Elsa.Extensions;
 using Elsa.Features.Services;
+using Elsa.Identity.Multitenancy;
 using Elsa.Persistence.EFCore.Extensions;
 using Elsa.Persistence.EFCore.Modules.Management;
 using Elsa.Persistence.EFCore.Modules.Runtime;
 using Elsa.Server.Web.Activities;
 using Elsa.Server.Web.ActivityHosts;
 using Elsa.Server.Web.Filters;
+using Elsa.Tenants;
 using Elsa.Tenants.AspNetCore;
 using Elsa.Tenants.Extensions;
 using Elsa.WorkflowProviders.BlobStorage.ElsaScript.Extensions;
@@ -29,7 +31,7 @@
 // ReSharper disable RedundantAssignment
 const bool useReadOnlyMode = false;
 const bool useSignalR = false; // Disabled until Elsa Studio sends authenticated requests.
-const bool useMultitenancy = false;
+const bool useMultitenancy = true;
 const bool disableVariableWrappers = false;
 
 ObjectConverter.StrictMode = true;
@@ -118,6 +120,17 @@
                 http.ConfigureHttpOptions = options => configuration.GetSection("Http").Bind(options);
                 http.UseCache();
             });
+
+        if(useMultitenancy)
+        {
+            elsa.UseTenants(tenants =>
+            {
+                tenants.UseConfigurationBasedTenantsProvider(options => configuration.GetSection("Multitenancy").Bind(options));
+                tenants.ConfigureMultitenancy(options => options.TenantResolverPipelineBuilder = new TenantResolverPipelineBuilder()
+                    .Append<CurrentUserTenantResolver>());
+            });
+        }
+
         ConfigureForTest?.Invoke(elsa);
     });
 

src/apps/Elsa.Server.Web/appsettings.json

@@ -39,6 +39,19 @@
             "Sqlite": "Data Source=App_Data/elsa.sqlite.db;Cache=Shared;"
           }
         }
+      },
+      {
+        "Id": "tenant-2",
+        "Name": "Tenant 2",
+        "Configuration": {
+          "Http": {
+            "Prefix": "tenant-2",
+            "Host": "localhost:5001"
+          },
+          "ConnectionStrings": {
+            "Sqlite": "Data Source=App_Data/elsa.sqlite.db;Cache=Shared;"
+          }
+        }
       }
     ]
   },

src/modules/Elsa.Common/Multitenancy/Abstractions/TenantResolverBase.cs

@@ -29,13 +29,13 @@ protected virtual TenantResolverResult Resolve(TenantResolverContext context)
     /// <summary>
     /// Creates a new instance of <see cref="TenantResolverResult"/> representing a resolved tenant.
     /// </summary>
-    protected TenantResolverResult Resolved(string tenantId) => new(tenantId);
-    
+    protected TenantResolverResult Resolved(string? tenantId) => TenantResolverResult.Resolved(tenantId);
+
     /// <summary>
     /// Creates a new instance of <see cref="TenantResolverResult"/> representing an unresolved tenant.
     /// </summary>
-    protected TenantResolverResult Unresolved() => new(null);
-    
+    protected TenantResolverResult Unresolved() => TenantResolverResult.Unresolved();
+
     /// <summary>
     /// Automatically resolves the tenant if the tenant ID is not null.
     /// </summary>

src/modules/Elsa.Common/Multitenancy/Contexts/TenantResolverContext.cs

@@ -30,9 +30,10 @@ public TenantResolverContext(IDictionary<string, Tenant> tenants, CancellationTo
     /// </summary>
     /// <param name="tenantId">The tenant ID.</param>
     /// <returns>The found tenant or null if no tenant with the provided ID exists.</returns>
-    public Tenant? FindTenant(string tenantId)
+    public Tenant? FindTenant(string? tenantId)
     {
-        return _tenantsDictionary.TryGetValue(tenantId, out var tenant) ? tenant : null;
+        var normalizedId = tenantId.NormalizeTenantId();
+        return _tenantsDictionary.TryGetValue(normalizedId, out var tenant) ? tenant : null;
     }
 
     /// <summary>

src/modules/Elsa.Common/Multitenancy/Contracts/ITenantResolver.cs

@@ -1,7 +1,7 @@
 namespace Elsa.Common.Multitenancy;
 
 /// <summary>
-/// A strategy for resolving the current tenant. This is called the tenant initializer.
+/// A strategy for resolving the current tenant, called from the tenant initializer.
 /// </summary>
 public interface ITenantResolver
 {

src/modules/Elsa.Common/Multitenancy/Entities/Tenant.cs

@@ -10,6 +10,11 @@ namespace Elsa.Common.Multitenancy;
 [UsedImplicitly]
 public class Tenant : Entity
 {
+    /// <summary>
+    /// The ID used for the default tenant.
+    /// </summary>
+    public const string DefaultTenantId = "";
+
     /// <summary>
     /// Gets or sets the name.
     /// </summary>
@@ -19,10 +24,10 @@ public class Tenant : Entity
     /// Gets or sets the configuration.
     /// </summary>
     public IConfiguration Configuration { get; set; } = new ConfigurationBuilder().Build();
-    
+
     public static readonly Tenant Default = new()
     {
-        Id = null!,
+        Id = DefaultTenantId,
         Name = "Default"
     };
 }

src/modules/Elsa.Common/Multitenancy/Extensions/TenantsProviderExtensions.cs

@@ -5,6 +5,11 @@ namespace Elsa.Common.Multitenancy;
 [UsedImplicitly]
 public static class TenantsProviderExtensions
 {
+    /// <summary>
+    /// Normalizes a tenant ID by converting null to empty string, ensuring consistency with the default tenant convention.
+    /// </summary>
+    public static string NormalizeTenantId(this string? tenantId) => tenantId ?? Tenant.DefaultTenantId;
+
     public static async Task<Tenant?> FindByIdAsync(this ITenantsProvider tenantsProvider, string id, CancellationToken cancellationToken = default)
     {
         var filter = new TenantFilter

src/modules/Elsa.Common/Multitenancy/Results/TenantResolverResult.cs

@@ -3,26 +3,38 @@ namespace Elsa.Common.Multitenancy;
 /// <summary>
 /// Represents the result of a tenant resolution.
 /// </summary>
-/// <param name="TenantId">The resolved tenant.</param>
-public record TenantResolverResult(string? TenantId)
+public record TenantResolverResult
 {
+    private readonly bool _isResolved;
+
+    private TenantResolverResult(string? tenantId, bool isResolved)
+    {
+        TenantId = tenantId;
+        _isResolved = isResolved;
+    }
+
+    /// <summary>
+    /// The normalized tenant ID. Returns null if unresolved.
+    /// </summary>
+    public string? TenantId => _isResolved ? field.NormalizeTenantId() : null;
+
     /// <summary>
     /// Creates a new instance of <see cref="TenantResolverResult"/> representing a resolved tenant.
     /// </summary>
     /// <param name="tenantId">The resolved tenant.</param>
     /// <returns>A new instance of <see cref="TenantResolverResult"/> representing a resolved tenant.</returns>
-    public static TenantResolverResult Resolved(string tenantId) => new(tenantId);
-    
+    public static TenantResolverResult Resolved(string? tenantId) => new(tenantId, true);
+
     /// <summary>
     /// Creates a new instance of <see cref="TenantResolverResult"/> representing an unresolved tenant.
     /// </summary>
     /// <returns>A new instance of <see cref="TenantResolverResult"/> representing an unresolved tenant.</returns>
-    public static TenantResolverResult Unresolved() => new(default(string?));
-    
+    public static TenantResolverResult Unresolved() => new(null, false);
+
     /// <summary>
     /// Gets a value indicating whether the tenant has been resolved.
     /// </summary>
-    public bool IsResolved => TenantId != null;
-    
+    public bool IsResolved => _isResolved;
+
     public string ResolveTenantId() => TenantId ?? throw new InvalidOperationException("Tenant has not been resolved.");
 }

src/modules/Elsa.Persistence.EFCore.Common/PersistenceFeatureBase.cs

@@ -2,6 +2,7 @@
 using Elsa.Extensions;
 using Elsa.Features.Abstractions;
 using Elsa.Features.Services;
+using Elsa.Persistence.EFCore.EntityHandlers;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.EntityFrameworkCore.Diagnostics;
 using Microsoft.Extensions.DependencyInjection;
@@ -60,6 +61,9 @@ public override void Apply()
         {
             options.RunMigrations[typeof(TDbContext)] = RunMigrations;
         });
+
+        Services.AddScoped<IEntitySavingHandler, ApplyTenantId>();
+        Services.AddScoped<IEntityModelCreatingHandler, SetTenantIdFilter>();
     }
 
     protected virtual void ConfigureMigrations()

src/modules/Elsa.Persistence.EFCore.MySql/Migrations/Runtime/20251204150235_V3_6.cs

@@ -30,18 +30,18 @@ protected override void Up(MigrationBuilder migrationBuilder)
                 .OldAnnotation("MySql:CharSet", "utf8mb4");
 
             migrationBuilder.CreateIndex(
-                name: "IX_StoredTrigger_Unique_WorkflowDefinitionId_Hash_ActivityId",
+                name: "IX_StoredTrigger_Unique_WorkflowDefinitionId_Hash_ActivityId_TenantId",
                 schema: _schema.Schema,
                 table: "Triggers",
-                columns: new[] { "WorkflowDefinitionId", "Hash", "ActivityId" },
+                columns: new[] { "WorkflowDefinitionId", "Hash", "ActivityId", "TenantId" },
                 unique: true);
         }
 
         /// <inheritdoc />
         protected override void Down(MigrationBuilder migrationBuilder)
         {
             migrationBuilder.DropIndex(
-                name: "IX_StoredTrigger_Unique_WorkflowDefinitionId_Hash_ActivityId",
+                name: "IX_StoredTrigger_Unique_WorkflowDefinitionId_Hash_ActivityId_TenantId",
                 schema: _schema.Schema,
                 table: "Triggers");