Fix Json Schema validations for optional fields (#2611)

## Why make this change?

- Closes #2542 
- Schema validation is incorrectly raising failure when optional fields
are not present.
- This change will ensure optional fields are correctly evaluated during
schema validation.

## What is this change?

- updated the `dab.draft.schema.json` optional field types with `null`
to allow for optional fields to be evaluated correctly during schema
validation.

## How was this tested?

- [X] Manual Tests
- [X] Unit Tests

## Sample Request(s)
config: 

![image](https://github.com/user-attachments/assets/e93f83a4-0552-4471-b364-3dd095ab7fba)

Before Fix:

![image](https://github.com/user-attachments/assets/5c6ba6c6-1ba5-465f-ac1f-b4e3b1d08b24)

After Fix:

![image](https://github.com/user-attachments/assets/c6135189-0cad-44c2-bb5d-eb588d115c6a)

---------

Co-authored-by: sezalchug <[email protected]>

Author: abhishekkumams

schemas/dab.draft.schema.json

@@ -245,15 +245,15 @@
             },
             "mode": {
               "description": "Set if running in Development or Production mode",
-              "type": "string",
+              "type": ["string", "null"],
               "default": "production",
               "enum": [
                 "production",
                 "development"
               ]
             },
             "cors": {
-              "type": "object",
+              "type": ["object", "null"],
               "description": "Configure CORS",
               "additionalProperties": false,
               "properties": {
@@ -273,7 +273,7 @@
               }
             },
             "authentication": {
-              "type": "object",
+              "type": ["object", "null"],
               "additionalProperties": false,
               "properties": {
                 "provider": {

src/Service.Tests/Configuration/ConfigurationTests.cs

@@ -467,6 +467,69 @@ type Moon {
 }
 ";
 
+        public const string CONFIG_FILE_WITH_NO_OPTIONAL_FIELD = @"{
+                                    ""$schema"":""https://github.com/Azure/data-api-builder/releases/download/vmajor.minor.patch-alpha/dab.draft.schema.json"",
+                                    ""data-source"": {
+                                    ""database-type"": ""mssql"",
+                                    ""connection-string"": ""sample-conn-string""
+                                    },
+                                    ""entities"":{ }
+                                }";
+
+        public const string CONFIG_FILE_WITH_NO_AUTHENTICATION_FIELD = @"{
+                                    // Link for latest draft schema.
+                                    ""$schema"":""https://github.com/Azure/data-api-builder/releases/download/vmajor.minor.patch-alpha/dab.draft.schema.json"",
+                                    ""data-source"": {
+                                    ""database-type"": ""mssql"",
+                                    ""connection-string"": ""sample-conn-string""
+                                    },
+                                    ""runtime"": {
+                                        ""rest"": {
+                                            ""enabled"": true,
+                                            ""path"": ""/api""
+                                        },
+                                        ""graphql"": {
+                                            ""enabled"": true,
+                                            ""path"": ""/graphql"",
+                                            ""allow-introspection"": true
+                                        },
+                                        ""host"": {
+                                            ""cors"": {
+                                                ""origins"": [
+                                                    ""http://localhost:5000""
+                                                ],
+                                                ""allow-credentials"": false
+                                            }
+                                        }
+                                    },
+                                    ""entities"":{ }
+                                }";
+        public const string CONFIG_FILE_WITH_NO_CORS_FIELD = @"{
+                                    // Link for latest draft schema.
+                                    ""$schema"":""https://github.com/Azure/data-api-builder/releases/download/vmajor.minor.patch-alpha/dab.draft.schema.json"",
+                                    ""data-source"": {
+                                    ""database-type"": ""mssql"",
+                                    ""connection-string"": ""sample-conn-string""
+                                    },
+                                    ""runtime"": {
+                                        ""rest"": {
+                                            ""enabled"": true,
+                                            ""path"": ""/api""
+                                        },
+                                        ""graphql"": {
+                                            ""enabled"": true,
+                                            ""path"": ""/graphql"",
+                                            ""allow-introspection"": true
+                                        },
+                                        ""host"": {
+                                            ""authentication"": {
+                                                ""provider"": ""StaticWebApps""
+                                            }
+                                        }
+                                    },
+                                    ""entities"":{ }
+                                }";
+
         [TestCleanup]
         public void CleanupAfterEachTest()
         {
@@ -1590,6 +1653,64 @@ public async Task TestConfigSchemaIsValid()
                 Times.Once);
         }
 
+        /// <summary>
+        /// This test method validates a sample DAB runtime config file against DAB's JSON schema definition.
+        /// It asserts that the validation is successful and there are no validation failures when no optional fields are used.
+        /// It also verifies that the expected log message is logged.
+        /// </summary>
+        [DataTestMethod]
+        [DataRow(CONFIG_FILE_WITH_NO_OPTIONAL_FIELD, DisplayName = "Validates schema of the config file with no optional fields.")]
+        [DataRow(CONFIG_FILE_WITH_NO_AUTHENTICATION_FIELD, DisplayName = "Validates schema of the config file with no Authentication field.")]
+        [DataRow(CONFIG_FILE_WITH_NO_CORS_FIELD, DisplayName = "Validates schema of the config file with no Cors field.")]
+        public async Task TestBasicConfigSchemaWithNoOptionalFieldsIsValid(string jsonData)
+        {
+            Mock<ILogger<JsonConfigSchemaValidator>> schemaValidatorLogger = new();
+
+            string jsonSchema = File.ReadAllText("dab.draft.schema.json");
+
+            JsonConfigSchemaValidator jsonSchemaValidator = new(schemaValidatorLogger.Object, new MockFileSystem());
+
+            JsonSchemaValidationResult result = await jsonSchemaValidator.ValidateJsonConfigWithSchemaAsync(jsonSchema, jsonData);
+            Assert.IsTrue(result.IsValid);
+            Assert.IsTrue(EnumerableUtilities.IsNullOrEmpty(result.ValidationErrors));
+            schemaValidatorLogger.Verify(
+                x => x.Log(
+                    LogLevel.Information,
+                    It.IsAny<EventId>(),
+                    It.Is<It.IsAnyType>((o, t) => o.ToString()!.Contains($"The config satisfies the schema requirements.")),
+                    It.IsAny<Exception>(),
+                    (Func<It.IsAnyType, Exception, string>)It.IsAny<object>()),
+                Times.Once);
+        }
+
+        /// <summary>
+        /// The config file does not contain any entity fields, which is expected to be invalid according to the schema.
+        /// The test asserts that the validation fails and there are validation errors.
+        /// It also verifies that the expected error message is logged, indicating that the 'entities' property is required.
+        [TestMethod]
+        public async Task TestBasicConfigSchemaWithNoEntityFieldsIsInvalid()
+        {
+            string jsonData = @"{
+                                    ""$schema"":""https://github.com/Azure/data-api-builder/releases/download/vmajor.minor.patch-alpha/dab.draft.schema.json"",
+                                    ""data-source"": {
+                                    ""database-type"": ""mssql"",
+                                    ""connection-string"": ""sample-conn-string""
+                                    }
+                                }";
+
+            Mock<ILogger<JsonConfigSchemaValidator>> schemaValidatorLogger = new();
+
+            string jsonSchema = File.ReadAllText("dab.draft.schema.json");
+
+            JsonConfigSchemaValidator jsonSchemaValidator = new(schemaValidatorLogger.Object, new MockFileSystem());
+
+            JsonSchemaValidationResult result = await jsonSchemaValidator.ValidateJsonConfigWithSchemaAsync(jsonSchema, jsonData);
+            Assert.IsFalse(result.IsValid);
+            Assert.IsFalse(EnumerableUtilities.IsNullOrEmpty(result.ValidationErrors));
+            Assert.AreEqual(1, result.ErrorCount);
+            Assert.IsTrue(result.ErrorMessage.Contains("Total schema validation errors: 1\n> PropertyRequired: #/entities"));
+        }
+
         /// <summary>
         /// This test tries to validate a runtime config file that is not compliant with the runtime config JSON schema.
         /// It validates no additional properties are defined in the config file.