Improve GraphQL naming conflict error to identify conflicting entities and operations

src/Core/Configurations/RuntimeConfigValidator.cs

@@ -909,6 +909,9 @@ public void ValidateEntitiesDoNotGenerateDuplicateQueriesOrMutation(DatabaseType
     {
         HashSet<string> graphQLOperationNames = new();
 
+        // Tracks which entity registered each operation name, used only for building conflict error messages.
+        Dictionary<string, string> operationOwner = new();
+
         foreach ((string entityName, Entity entity) in entityCollection)
         {
             if (!entity.GraphQL.Enabled)
@@ -917,6 +920,7 @@ public void ValidateEntitiesDoNotGenerateDuplicateQueriesOrMutation(DatabaseType
             }
 
             bool containsDuplicateOperationNames = false;
+            string conflictingEntityName = string.Empty;
             if (entity.Source.Type is EntitySourceType.StoredProcedure)
             {
                 // For Stored Procedures a single query/mutation is generated.
@@ -925,6 +929,11 @@ public void ValidateEntitiesDoNotGenerateDuplicateQueriesOrMutation(DatabaseType
                 if (!graphQLOperationNames.Add(storedProcedureQueryName))
                 {
                     containsDuplicateOperationNames = true;
+                    conflictingEntityName = operationOwner.GetValueOrDefault(storedProcedureQueryName, string.Empty);
+                }
+                else
+                {
+                    operationOwner[storedProcedureQueryName] = entityName;
                 }
             }
             else
@@ -951,13 +960,41 @@ public void ValidateEntitiesDoNotGenerateDuplicateQueriesOrMutation(DatabaseType
                     || ((databaseType is DatabaseType.CosmosDB_NoSQL) && !graphQLOperationNames.Add(patchMutationName)))
                 {
                     containsDuplicateOperationNames = true;
+                    conflictingEntityName =
+                        operationOwner.GetValueOrDefault(pkQueryName) ??
+                        operationOwner.GetValueOrDefault(listQueryName) ??
+                        operationOwner.GetValueOrDefault(createMutationName) ??
+                        operationOwner.GetValueOrDefault(updateMutationName) ??
+                        operationOwner.GetValueOrDefault(deleteMutationName) ??
+                        operationOwner.GetValueOrDefault(patchMutationName) ??
+                        string.Empty;
+                }
+                else
+                {
+                    operationOwner[pkQueryName] = entityName;
+                    operationOwner[listQueryName] = entityName;
+                    operationOwner[createMutationName] = entityName;
+                    operationOwner[updateMutationName] = entityName;
+                    operationOwner[deleteMutationName] = entityName;
+                    if (databaseType is DatabaseType.CosmosDB_NoSQL)
+                    {
+                        operationOwner[patchMutationName] = entityName;
+                    }
                 }
             }
 
             if (containsDuplicateOperationNames)
             {
+                string entitiesStr = string.IsNullOrEmpty(conflictingEntityName)
+                    ? $"  {entityName}"
+                    : $"  {conflictingEntityName}{Environment.NewLine}  {entityName}";
+
+                string message = $"GraphQL naming conflict detected.{Environment.NewLine}"
+                    + $"{Environment.NewLine}Entities:{Environment.NewLine}{entitiesStr}"
+                    + $"{Environment.NewLine}{Environment.NewLine}Configure distinct GraphQL singular and plural names for one of the entities to resolve this conflict.";
+
                 HandleOrRecordException(new DataApiBuilderException(
-                    message: $"Entity {entityName} generates queries/mutation that already exist",
+                    message: message,
                     statusCode: HttpStatusCode.ServiceUnavailable,
                     subStatusCode: DataApiBuilderException.SubStatusCodes.ConfigValidationError));
             }

src/Service.Tests/UnitTests/ConfigValidationUnitTests.cs

@@ -1259,7 +1259,7 @@ public void ValidateEntitiesWithGraphQLExposedGenerateDuplicateQueries(DatabaseT
                 { "book", book },
                 { "Book", bookWithUpperCase }
             };
-            ValidateExceptionForDuplicateQueriesDueToEntityDefinitions(entityCollection, "Book", databaseType);
+            ValidateExceptionForDuplicateQueriesDueToEntityDefinitions(entityCollection, "Book", databaseType, conflictingEntityName: "book");
         }
 
         /// <summary>
@@ -1302,7 +1302,7 @@ public void ValidateStoredProcedureAndTableGeneratedDuplicateQueries(DatabaseTyp
                 { "executeBook", bookTable },
                 { "Book_by_pk", bookByPkStoredProcedure }
             };
-            ValidateExceptionForDuplicateQueriesDueToEntityDefinitions(entityCollection, "executeBook", databaseType);
+            ValidateExceptionForDuplicateQueriesDueToEntityDefinitions(entityCollection, "executeBook", databaseType, conflictingEntityName: "Book_by_pk");
         }
 
         /// <summary>
@@ -1346,7 +1346,7 @@ public void ValidateStoredProcedureAndTableGeneratedDuplicateMutation(DatabaseTy
                 { "ExecuteBooks", bookTable },
                 { "AddBook", addBookStoredProcedure }
             };
-            ValidateExceptionForDuplicateQueriesDueToEntityDefinitions(entityCollection, "ExecuteBooks", databaseType);
+            ValidateExceptionForDuplicateQueriesDueToEntityDefinitions(entityCollection, "ExecuteBooks", databaseType, conflictingEntityName: "AddBook");
         }
 
         /// <summary>
@@ -1384,7 +1384,7 @@ public void ValidateEntitiesWithNameCollisionInGraphQLTypeGenerateDuplicateQueri
                 { "book", book },
                 { "book_alt", book_alt }
             };
-            ValidateExceptionForDuplicateQueriesDueToEntityDefinitions(entityCollection, "book_alt", databaseType);
+            ValidateExceptionForDuplicateQueriesDueToEntityDefinitions(entityCollection, "book_alt", databaseType, conflictingEntityName: "book");
         }
 
         /// <summary>
@@ -1427,7 +1427,7 @@ public void ValidateEntitiesWithCollisionsInSingularPluralNamesGenerateDuplicate
                 { "book", book },
                 { "book_alt", book_alt }
             };
-            ValidateExceptionForDuplicateQueriesDueToEntityDefinitions(entityCollection, "book_alt", databaseType);
+            ValidateExceptionForDuplicateQueriesDueToEntityDefinitions(entityCollection, "book_alt", databaseType, conflictingEntityName: "book");
         }
 
         /// <summary>
@@ -1465,7 +1465,45 @@ public void ValidateEntitiesWithNameCollisionInSingularPluralTypeGeneratesDuplic
 
             entityCollection.Add("book_alt", book_alt);
             entityCollection.Add("book", book);
-            ValidateExceptionForDuplicateQueriesDueToEntityDefinitions(entityCollection, "book_alt", databaseType);
+            ValidateExceptionForDuplicateQueriesDueToEntityDefinitions(entityCollection, "book_alt", databaseType, conflictingEntityName: "book");
+        }
+
+        /// <summary>
+        /// Validates that a detailed error is thrown when autoentities includes objects whose names
+        /// differ only by singular/plural form (e.g. dbo.Category and dbo.Categories), causing
+        /// DAB to generate conflicting GraphQL type and operation names.
+        ///
+        /// "dbo_Category" entity → singular: Category, plural: Categories
+        /// "dbo_Categories" entity → singular: Category, plural: Categories (after pluralization)
+        ///
+        /// Both entities generate the same pk query, list query, and mutation names.
+        /// </summary>
+        [TestMethod]
+        [DataRow(DatabaseType.MSSQL)] // Relational Database
+        [DataRow(DatabaseType.CosmosDB_NoSQL)] // Non Relational Database
+        public void ValidateAutoEntitiesWithSingularPluralNameCollisionGenerateDuplicateQueries(DatabaseType databaseType)
+        {
+            // Entity Name: dbo_Category
+            // Singular: Category (from entity name processed by autoentities)
+            // Plural: Categories (pluralized from singular)
+            Entity categoryEntity = GraphQLTestHelpers.GenerateEntityWithSingularPlural("Category", "Categories");
+
+            // Entity Name: dbo_Categories
+            // Singular: Category (after singularization by autoentities)
+            // Plural: Categories
+            Entity categoriesEntity = GraphQLTestHelpers.GenerateEntityWithSingularPlural("Category", "Categories");
+
+            SortedDictionary<string, Entity> entityCollection = new()
+            {
+                { "dbo_Categories", categoriesEntity },
+                { "dbo_Category", categoryEntity }
+            };
+
+            ValidateExceptionForDuplicateQueriesDueToEntityDefinitions(
+                entityCollection,
+                "dbo_Category",
+                databaseType,
+                conflictingEntityName: "dbo_Categories");
         }
 
         /// <summary>
@@ -1612,14 +1650,22 @@ public void TestGlobalRouteValidation(string graphQLConfiguredPath, string restC
         /// queries with the same name.
         /// </summary>
         /// <param name="entityCollection">Entity definitions</param>
-        /// <param name="entityName">Entity name to construct the expected exception message</param>
-        private static void ValidateExceptionForDuplicateQueriesDueToEntityDefinitions(SortedDictionary<string, Entity> entityCollection, string entityName, DatabaseType databaseType)
+        /// <param name="entityName">The entity name expected to appear in the conflict message as the conflicting entity.</param>
+        /// <param name="databaseType">Database type used during validation.</param>
+        /// <param name="conflictingEntityName">The other entity name expected to appear in the conflict message.</param>
+        private static void ValidateExceptionForDuplicateQueriesDueToEntityDefinitions(
+            SortedDictionary<string, Entity> entityCollection,
+            string entityName,
+            DatabaseType databaseType,
+            string conflictingEntityName)
         {
             RuntimeConfigValidator configValidator = InitializeRuntimeConfigValidator();
             DataApiBuilderException dabException = Assert.ThrowsException<DataApiBuilderException>(
                action: () => configValidator.ValidateEntitiesDoNotGenerateDuplicateQueriesOrMutation(databaseType, new(entityCollection)));
 
-            Assert.AreEqual(expected: $"Entity {entityName} generates queries/mutation that already exist", actual: dabException.Message);
+            StringAssert.StartsWith(dabException.Message, "GraphQL naming conflict detected.");
+            StringAssert.Contains(dabException.Message, entityName);
+            StringAssert.Contains(dabException.Message, conflictingEntityName);
             Assert.AreEqual(expected: HttpStatusCode.ServiceUnavailable, actual: dabException.StatusCode);
             Assert.AreEqual(expected: DataApiBuilderException.SubStatusCodes.ConfigValidationError, actual: dabException.SubStatusCode);
         }