Maintain Default Data Source Name from Original Config after Hot Reloading

src/Config/FileSystemRuntimeConfigLoader.cs

@@ -98,13 +98,26 @@ public string GetConfigFileName()
     public bool TryLoadConfig(
         string path,
         [NotNullWhen(true)] out RuntimeConfig? config,
-        bool replaceEnvVar = false)
+        bool replaceEnvVar = false,
+        string dataSourceName = "")
     {
         if (_fileSystem.File.Exists(path))
         {
             Console.WriteLine($"Loading config file from {path}.");
             string json = _fileSystem.File.ReadAllText(path);
-            return TryParseConfig(json, out config, connectionString: _connectionString, replaceEnvVar: replaceEnvVar);
+            bool isParsed = TryParseConfig(
+                json: json,
+                config: out config,
+                connectionString: _connectionString,
+                replaceEnvVar: replaceEnvVar);
+
+            if (isParsed && !string.IsNullOrEmpty(dataSourceName))
+            {
+                config!.UpdateDefaultDataSourceNameDependantDictionaries(dataSourceName);
+                config!.DefaultDataSourceName = dataSourceName;
+            }
+
+            return isParsed;
         }
         else
         {
@@ -124,9 +137,9 @@ public bool TryLoadConfig(
     /// <param name="replaceEnvVar">Whether to replace environment variable with its
     /// value or not while deserializing.</param>
     /// <returns>True if the config was loaded, otherwise false.</returns>
-    public override bool TryLoadKnownConfig([NotNullWhen(true)] out RuntimeConfig? config, bool replaceEnvVar = false)
+    public override bool TryLoadKnownConfig([NotNullWhen(true)] out RuntimeConfig? config, bool replaceEnvVar = false, string dataSourceName = "")
     {
-        return TryLoadConfig(ConfigFilePath, out config, replaceEnvVar);
+        return TryLoadConfig(ConfigFilePath, out config, replaceEnvVar, dataSourceName);
     }
 
     /// <summary>

src/Config/ObjectModel/RuntimeConfig.cs

@@ -130,7 +130,7 @@ Runtime.GraphQL is null ||
         }
     }
 
-    private string _defaultDataSourceName;
+    public string DefaultDataSourceName;
 
     private Dictionary<string, DataSource> _dataSourceNameToDataSource;
 
@@ -169,18 +169,18 @@ public RuntimeConfig(string? Schema, DataSource DataSource, RuntimeEntities Enti
         this.DataSource = DataSource;
         this.Runtime = Runtime;
         this.Entities = Entities;
-        _defaultDataSourceName = Guid.NewGuid().ToString();
+        DefaultDataSourceName = Guid.NewGuid().ToString();
 
         // we will set them up with default values
         _dataSourceNameToDataSource = new Dictionary<string, DataSource>
         {
-            { _defaultDataSourceName, this.DataSource }
+            { DefaultDataSourceName, this.DataSource }
         };
 
         _entityNameToDataSourceName = new Dictionary<string, string>();
         foreach (KeyValuePair<string, Entity> entity in Entities)
         {
-            _entityNameToDataSourceName.TryAdd(entity.Key, _defaultDataSourceName);
+            _entityNameToDataSourceName.TryAdd(entity.Key, DefaultDataSourceName);
         }
 
         // Process data source and entities information for each database in multiple database scenario.
@@ -241,7 +241,7 @@ public RuntimeConfig(string Schema, DataSource DataSource, RuntimeOptions Runtim
         this.DataSource = DataSource;
         this.Runtime = Runtime;
         this.Entities = Entities;
-        _defaultDataSourceName = DefaultDataSourceName;
+        this.DefaultDataSourceName = DefaultDataSourceName;
         _dataSourceNameToDataSource = DataSourceNameToDataSource;
         _entityNameToDataSourceName = EntityNameToDataSourceName;
         this.DataSourceFiles = DataSourceFiles;
@@ -273,6 +273,26 @@ public void UpdateDataSourceNameToDataSource(string dataSourceName, DataSource d
         _dataSourceNameToDataSource[dataSourceName] = dataSource;
     }
 
+    /// <summary>
+    /// In a Hot Reload scenario we should maintain the same default data source
+    /// name before the hot reload as after the hot reload. This method takes
+    /// a default data source name, such as the one from before hot reload, and
+    /// replaces the current dictionary entries of this RuntimeConfig that were
+    /// built using a new, unique guid during the construction of this RuntimeConfig
+    /// with entries using the provided default data source name.
+    /// </summary>
+    /// <param name="defaultDataSourceName">The name used to update the dictionaries.</param>
+    public void UpdateDefaultDataSourceNameDependantDictionaries(string defaultDataSourceName)
+    {
+        _dataSourceNameToDataSource.Remove(DefaultDataSourceName);
+        _dataSourceNameToDataSource.Add(defaultDataSourceName, this.DataSource);
+        foreach (KeyValuePair<string, Entity> entity in Entities)
+        {
+            _entityNameToDataSourceName.Remove(entity.Key);
+            _entityNameToDataSourceName.TryAdd(entity.Key, DefaultDataSourceName);
+        }
+    }
+
     /// <summary>
     /// Gets datasourceName from EntityNameToDatasourceName dictionary.
     /// </summary>
@@ -311,7 +331,7 @@ public bool CheckDataSourceExists(string dataSourceName)
     public string GetDefaultDataSourceName()
 #pragma warning restore CA1024 // Use properties where appropriate
     {
-        return _defaultDataSourceName;
+        return DefaultDataSourceName;
     }
 
     /// <summary>

src/Config/RuntimeConfigLoader.cs

@@ -34,7 +34,7 @@ public RuntimeConfigLoader(string? connectionString = null)
     /// <param name="replaceEnvVar">Whether to replace environment variable with its
     /// value or not while deserializing.</param>
     /// <returns>True if the config was loaded, otherwise false.</returns>
-    public abstract bool TryLoadKnownConfig([NotNullWhen(true)] out RuntimeConfig? config, bool replaceEnvVar = false);
+    public abstract bool TryLoadKnownConfig([NotNullWhen(true)] out RuntimeConfig? config, bool replaceEnvVar = false, string dataSourceName = "");
 
     /// <summary>
     /// Returns the link to the published draft schema.

src/Core/Configurations/ConfigFileWatcher.cs

@@ -38,7 +38,8 @@ private void OnConfigFileChange(object sender, FileSystemEventArgs e)
 
             if (!_configProvider.IsLateConfigured && _configProvider.GetConfig().IsDevelopmentMode())
             {
-                _configProvider.HotReloadConfig();
+                // pass along the original default data source name for consistency within runtime config's data structures
+                _configProvider.HotReloadConfig(_configProvider.GetConfig().DefaultDataSourceName);
             }
         }
         catch (Exception ex)

src/Core/Configurations/RuntimeConfigProvider.cs

@@ -149,9 +149,9 @@ public bool TryGetLoadedConfig([NotNullWhen(true)] out RuntimeConfig? runtimeCon
     /// Hot Reloads the runtime config when the file watcher
     /// is active and detects a change to the underlying config file.
     /// </summary>
-    public void HotReloadConfig()
+    public void HotReloadConfig(string dataSourceName)
     {
-        ConfigLoader.TryLoadKnownConfig(out _runtimeConfig, replaceEnvVar: true);
+        ConfigLoader.TryLoadKnownConfig(out _runtimeConfig, replaceEnvVar: true, dataSourceName: dataSourceName);
     }
 
     /// <summary>

src/Service.Tests/Unittests/ConfigFileWatcherUnitTests.cs

@@ -13,31 +13,17 @@ namespace Azure.DataApiBuilder.Service.Tests.Unittests
     [TestClass]
     public class ConfigFileWatcherUnitTests
     {
-        /// <summary>
-        /// Use the file system (not mocked) to create a hot reload
-        /// scenario of the REST runtime options and verify that we
-        /// correctly hot reload those options.
-        /// </summary>
-        [TestMethod]
-        public void HotReloadConfigRestRuntimeOptions()
-        {
-            string initialRestPath = "/api";
-            string updatedRestPath = "/rest";
-            string initialGQLPath = "/api";
-            string updatedGQLPath = "/gql";
-
-            bool initialRestEnabled = true;
-            bool updatedRestEnabled = false;
-            bool initialGQLEnabled = true;
-            bool updatedGQLEnabled = false;
-
-            bool initialGQLIntrospection = true;
-            bool updatedGQLIntrospection = false;
 
-            HostMode initialMode = HostMode.Development;
-            HostMode updatedMode = HostMode.Production;
-
-            string initialConfig = @"
+        private static string GenerateRuntimeSectionStringFromParams(
+            string restPath,
+            string gqlPath,
+            bool restEnabled,
+            bool gqlEnabled,
+            bool gqlIntrospection,
+            HostMode mode
+            )
+        {
+            string runtimeString = @"
 {
   ""$schema"": ""https://github.com/Azure/data-api-builder/releases/download/vmajor.minor.patch/dab.draft.schema.json"",
   ""data-source"": {
@@ -49,13 +35,13 @@ public void HotReloadConfigRestRuntimeOptions()
   },
   ""runtime"": {
     ""rest"": {
-      ""enabled"": " + initialRestEnabled.ToString().ToLower() + @",
-      ""path"": """ + initialRestPath + @"""
+      ""enabled"": " + restEnabled.ToString().ToLower() + @",
+      ""path"": """ + restPath + @"""
     },
     ""graphql"": {
-      ""enabled"": " + initialGQLEnabled.ToString().ToLower() + @",
-      ""path"": """ + initialGQLPath + @""",
-      ""allow-introspection"": " + initialGQLIntrospection.ToString().ToLower() + @"
+      ""enabled"": " + gqlEnabled.ToString().ToLower() + @",
+      ""path"": """ + gqlPath + @""",
+      ""allow-introspection"": " + gqlIntrospection.ToString().ToLower() + @"
     },
     ""host"": {
       ""cors"": {
@@ -67,46 +53,54 @@ public void HotReloadConfigRestRuntimeOptions()
       ""authentication"": {
         ""provider"": ""StaticWebApps""
       },
-      ""mode"": """ + initialMode + @"""
-    }
-  },
-  ""entities"": {}
-}";
-            string updatedConfig = @"
-{
-  ""$schema"": ""https://github.com/Azure/data-api-builder/releases/download/vmajor.minor.patch/dab.draft.schema.json"",
-  ""data-source"": {
-    ""database-type"": ""mssql"",
-    ""connection-string"": ""Server=test;Database=test;User ID=test"",
-    ""options"": {
-      ""set-session-context"": true
-    }
-  },
-  ""runtime"": {
-    ""rest"": {
-      ""enabled"": " + updatedRestEnabled.ToString().ToLower() + @",
-      ""path"": """ + updatedRestPath + @"""
-    },
-    ""graphql"": {
-      ""enabled"": " + updatedGQLEnabled.ToString().ToLower() + @",
-      ""path"": """ + updatedGQLPath + @""",
-      ""allow-introspection"": " + updatedGQLIntrospection.ToString().ToLower() + @"
-    },
-    ""host"": {
-      ""cors"": {
-        ""origins"": [
-          ""http://localhost:5000""
-        ],
-        ""allow-credentials"": false
-      },
-      ""authentication"": {
-        ""provider"": ""StaticWebApps""
-      },
-      ""mode"": """ + updatedMode + @"""
+      ""mode"": """ + mode + @"""
     }
   },
   ""entities"": {}
 }";
+            return runtimeString;
+        }
+
+        /// <summary>
+        /// Use the file system (not mocked) to create a hot reload
+        /// scenario of the REST runtime options and verify that we
+        /// correctly hot reload those options.
+        /// </summary>
+        [TestMethod]
+        public void HotReloadConfigRestRuntimeOptions()
+        {
+            string initialRestPath = "/api";
+            string updatedRestPath = "/rest";
+            string initialGQLPath = "/api";
+            string updatedGQLPath = "/gql";
+
+            bool initialRestEnabled = true;
+            bool updatedRestEnabled = false;
+            bool initialGQLEnabled = true;
+            bool updatedGQLEnabled = false;
+
+            bool initialGQLIntrospection = true;
+            bool updatedGQLIntrospection = false;
+
+            HostMode initialMode = HostMode.Development;
+            HostMode updatedMode = HostMode.Production;
+
+            string initialConfig = GenerateRuntimeSectionStringFromParams(
+                initialRestPath,
+                initialGQLPath,
+                initialRestEnabled,
+                initialGQLEnabled,
+                initialGQLIntrospection,
+                initialMode);
+
+            string updatedConfig = GenerateRuntimeSectionStringFromParams(
+                updatedRestPath,
+                updatedGQLPath,
+                updatedRestEnabled,
+                updatedGQLEnabled,
+                updatedGQLIntrospection,
+                updatedMode);
+
             string configName = "hotreload-config.json";
             if (File.Exists(configName))
             {
@@ -120,6 +114,7 @@ public void HotReloadConfigRestRuntimeOptions()
             RuntimeConfigProvider configProvider = new(configLoader);
             // Must GetConfig() to start file watching
             RuntimeConfig runtimeConfig = configProvider.GetConfig();
+            string initialDefaultDataSourceName = runtimeConfig.DefaultDataSourceName;
             // assert we have a valid config
             Assert.IsNotNull(runtimeConfig);
             Assert.AreEqual(initialRestEnabled, runtimeConfig.Runtime.Rest.Enabled);
@@ -134,12 +129,15 @@ public void HotReloadConfigRestRuntimeOptions()
             System.Threading.Thread.Sleep(1000);
             // Hot Reloaded config
             runtimeConfig = configProvider.GetConfig();
+            string updatedDefaultDataSourceName = runtimeConfig.DefaultDataSourceName;
             Assert.AreEqual(updatedRestEnabled, runtimeConfig.Runtime.Rest.Enabled);
             Assert.AreEqual(updatedRestPath, runtimeConfig.Runtime.Rest.Path);
             Assert.AreEqual(updatedGQLEnabled, runtimeConfig.Runtime.GraphQL.Enabled);
             Assert.AreEqual(updatedGQLPath, runtimeConfig.Runtime.GraphQL.Path);
             Assert.AreEqual(updatedGQLIntrospection, runtimeConfig.Runtime.GraphQL.AllowIntrospection);
             Assert.AreEqual(updatedMode, runtimeConfig.Runtime.Host.Mode);
+            // DefaultDataSourceName should not change after a hot reload.
+            Assert.AreEqual(initialDefaultDataSourceName, updatedDefaultDataSourceName);
             if (File.Exists(configName))
             {
                 File.Delete(configName);