Cosmos DB: Adds circular reference check for entities in graphQL schema

src/Core/Services/MetadataProviders/CosmosSqlMetadataProvider.cs

@@ -187,26 +187,48 @@ private void ParseSchemaGraphQLFieldsForJoins()
         /// 4. Check if we get previous entity with join information, if yes append it to the current entity also
         /// 5. Recursively call this function, to process the schema
         /// </summary>
-        /// <param name="fields"></param>
-        /// <param name="schemaDocument"></param>
-        /// <param name="currentPath"></param>
-        /// <param name="previousEntity">indicates the parent entity for which we are processing the schema.</param>
-        private void ProcessSchema(IReadOnlyList<FieldDefinitionNode> fields,
+        /// <param name="fields">All the fields of an entity</param>
+        /// <param name="schemaDocument">Schema Documents, useful to get fields information of an entity</param>
+        /// <param name="currentPath">Generated path of an entity</param>
+        /// <param name="tableCounter">Counter used to generate table alias</param>
+        /// <param name="parentEntity">indicates the parent entity for which we are processing the schema.
+        /// It is useful to get the JOIN statement information and create further new statements</param>
+        /// <param name="visitedEntities"> Keeps a track of the path in an entity, to detect circular reference</param>
+        /// <remarks>It detects the circular reference in the schema while processing the schema and throws <seealso cref="DataApiBuilderException"/> </remarks>
+        private void ProcessSchema(
+            IReadOnlyList<FieldDefinitionNode> fields,
             Dictionary<string, ObjectTypeDefinitionNode> schemaDocument,
             string currentPath,
             IncrementingInteger tableCounter,
-            EntityDbPolicyCosmosModel? previousEntity = null)
+            EntityDbPolicyCosmosModel? parentEntity = null,
+            HashSet<string>? visitedEntities = null)
         {
             // Traverse the fields and add them to the path
             foreach (FieldDefinitionNode field in fields)
             {
-                string entityType = field.Type.NamedType().Name.Value;
-                // If the entity is not in the runtime config, skip it
-                if (!_runtimeConfig.Entities.ContainsKey(entityType))
+                // Create a tracker to keep track of visited entities to detect circular references
+                HashSet<string> trackerForFields = new();
+                if (visitedEntities is not null)
+                {
+                    trackerForFields = visitedEntities;
+                }
+
+                // If the entity is build-in type, do not go further to check circular reference
+                if (GraphQLUtils.IsBuiltInType(field.Type))
                 {
                     continue;
                 }
 
+                string entityType = field.Type.NamedType().Name.Value;
+                // If the entity is already visited, then it is a circular reference
+                if (!trackerForFields.Add(entityType))
+                {
+                    throw new DataApiBuilderException(
+                        message: $"Circular reference detected in the provided GraphQL schema for entity '{entityType}'.",
+                        statusCode: System.Net.HttpStatusCode.InternalServerError,
+                        subStatusCode: DataApiBuilderException.SubStatusCodes.ErrorInInitialization);
+                }
+
                 string? alias = null;
                 bool isArrayType = field.Type is ListTypeNode;
                 if (isArrayType)
@@ -235,15 +257,15 @@ private void ParseSchemaGraphQLFieldsForJoins()
                         });
                 }
 
-                if (previousEntity is not null)
+                if (parentEntity is not null)
                 {
                     if (string.IsNullOrEmpty(currentEntity.JoinStatement))
                     {
-                        currentEntity.JoinStatement = previousEntity.JoinStatement;
+                        currentEntity.JoinStatement = parentEntity.JoinStatement;
                     }
                     else
                     {
-                        currentEntity.JoinStatement = previousEntity.JoinStatement + " JOIN " + currentEntity.JoinStatement;
+                        currentEntity.JoinStatement = parentEntity.JoinStatement + " JOIN " + currentEntity.JoinStatement;
                     }
                 }
 
@@ -253,7 +275,8 @@ private void ParseSchemaGraphQLFieldsForJoins()
                     schemaDocument: schemaDocument,
                     currentPath: isArrayType ? $"{alias}" : $"{currentPath}.{field.Name.Value}",
                     tableCounter: tableCounter,
-                    previousEntity: isArrayType ? currentEntity : null);
+                    parentEntity: isArrayType ? currentEntity : null,
+                    visitedEntities: trackerForFields);
             }
         }
 

src/Service.Tests/Configuration/ConfigurationTests.cs

@@ -425,6 +425,48 @@ public class ConfigurationTests
             }
         }";
 
+        internal const string GRAPHQL_SCHEMA_WITH_CYCLE_ARRAY = @"
+type Character {
+    id : ID,
+    name : String,
+    moons: [Moon],
+}
+
+type Planet @model(name:""Planet"") {
+    id : ID!,
+    name : String,
+    character: Character
+}
+
+type Moon {
+    id : ID,
+    name : String,
+    details : String,
+    character: Character
+}
+";
+
+        internal const string GRAPHQL_SCHEMA_WITH_CYCLE_OBJECT = @"
+type Character {
+    id : ID,
+    name : String,
+    moons: Moon,
+}
+
+type Planet @model(name:""Planet"") {
+    id : ID!,
+    name : String,
+    character: Character
+}
+
+type Moon {
+    id : ID,
+    name : String,
+    details : String,
+    character: Character
+}
+";
+
         [TestCleanup]
         public void CleanupAfterEachTest()
         {
@@ -2938,6 +2980,41 @@ public async Task TestEngineSupportViewsWithoutKeyFieldsInConfigForMsSQL()
             }
         }
 
+        /// <summary>
+        /// In CosmosDB NoSQL, we store data in the form of JSON. Practically, JSON can be very complex.
+        /// But DAB doesn't support JSON with circular references e.g if 'Character.Moon' is a valid JSON Path, then
+        /// 'Moon.Character' should not be there, DAB would throw an exception during the load itself.
+        /// </summary>
+        /// <exception cref="ApplicationException"></exception>
+        [TestMethod, TestCategory(TestCategory.COSMOSDBNOSQL)]
+        [DataRow(GRAPHQL_SCHEMA_WITH_CYCLE_OBJECT, DisplayName = "When Circular Reference is there with Object type (i.e. 'Moon' in 'Character' Entity")]
+        [DataRow(GRAPHQL_SCHEMA_WITH_CYCLE_ARRAY, DisplayName = "When Circular Reference is there with Array type (i.e. '[Moon]' in 'Character' Entity")]
+        public void ValidateGraphQLSchemaForCircularReference(string schema)
+        {
+            // Read the base config from the file system
+            TestHelper.SetupDatabaseEnvironment(TestCategory.COSMOSDBNOSQL);
+            FileSystemRuntimeConfigLoader baseLoader = TestHelper.GetRuntimeConfigLoader();
+            if (!baseLoader.TryLoadKnownConfig(out RuntimeConfig baseConfig))
+            {
+                throw new ApplicationException("Failed to load the default CosmosDB_NoSQL config and cannot continue with tests.");
+            }
+
+            // Setup a mock file system, and use that one with the loader/provider for the config
+            MockFileSystem fileSystem = new(new Dictionary<string, MockFileData>()
+            {
+                { @"../schema.gql", new MockFileData(schema) },
+                { DEFAULT_CONFIG_FILE_NAME, new MockFileData(baseConfig.ToJson()) }
+            });
+            FileSystemRuntimeConfigLoader loader = new(fileSystem);
+            RuntimeConfigProvider provider = new(loader);
+
+            DataApiBuilderException exception =
+                Assert.ThrowsException<DataApiBuilderException>(() => new CosmosSqlMetadataProvider(provider, fileSystem));
+            Assert.AreEqual("Circular reference detected in the provided GraphQL schema for entity 'Character'.", exception.Message);
+            Assert.AreEqual(HttpStatusCode.InternalServerError, exception.StatusCode);
+            Assert.AreEqual(DataApiBuilderException.SubStatusCodes.ErrorInInitialization, exception.SubStatusCode);
+        }
+
         /// <summary>
         /// When you query, DAB loads schema and check for defined entities in the config file which get load during DAB initialization, and
         /// it fails during this check if entity is not defined in the config file. In this test case, we are testing the error message is appropriate.