From 044aeb5165c083cc9f92fb473cc012458a85e7a8 Mon Sep 17 00:00:00 2001
From: aaronburtle <93220300+aaronburtle@users.noreply.github.com>
Date: Thu, 3 Sep 2026 00:31:54 +0000
Subject: [PATCH] Fix whitespace handling in MCP read_records select lists
 (#3786)

## Why make this change?

Closes https://github.com/Azure/data-api-builder/issues/3771

## What is this change?

- Trim whitespace from each field after splitting the comma-separated
`select` value.
- Add a regression integration test covering a space after the comma.

## How was this tested?

- [x] Integration Tests
- Added
`ReadRecords_WithWhitespaceAfterSelectComma_ReturnsSelectedFields`.
- [x] Unit Tests
  - All 309 non-database MCP tests passed.
  - The service test project builds successfully.

## Sample Request(s)

Example MCP `read_records` arguments:

    {
      "entity": "Book",
      "select": "id, title"
    }

The request now succeeds and returns the selected `id` and `title`
fields.

CLI, REST, and GraphQL samples are not applicable because this change
affects the MCP `read_records` tool only.

(cherry picked from commit dfd3be4c8ffac6ba227d52793f58a04f1878e922)
---
 .../BuiltInTools/ReadRecordsTool.cs           |  7 +++-
 .../ReadRecordsToolMsSqlIntegrationTests.cs   | 33 +++++++++++++++++++
 2 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/src/Azure.DataApiBuilder.Mcp/BuiltInTools/ReadRecordsTool.cs b/src/Azure.DataApiBuilder.Mcp/BuiltInTools/ReadRecordsTool.cs
index 8da3c4856a..bd33dd8433 100644
--- a/src/Azure.DataApiBuilder.Mcp/BuiltInTools/ReadRecordsTool.cs
+++ b/src/Azure.DataApiBuilder.Mcp/BuiltInTools/ReadRecordsTool.cs
@@ -201,7 +201,12 @@ public async Task<CallToolResult> ExecuteAsync(
                 if (!string.IsNullOrWhiteSpace(select))
                 {
                     // Update the context to specify which fields will be returned from the entity.
-                    IEnumerable<string> fieldsReturnedForFind = select.Split(",").ToList();
+                    List<string> fieldsReturnedForFind = select.Split(',').Select(field => field.Trim()).ToList();
+                    if (fieldsReturnedForFind.Any(string.IsNullOrEmpty))
+                    {
+                        return McpResponseBuilder.BuildErrorResult(toolName, "InvalidArguments", "The 'select' argument cannot contain empty field names.", logger);
+                    }
+
                     context.UpdateReturnFields(fieldsReturnedForFind);
                 }
 
diff --git a/src/Service.Tests/Mcp/ReadRecordsToolMsSqlIntegrationTests.cs b/src/Service.Tests/Mcp/ReadRecordsToolMsSqlIntegrationTests.cs
index 26e07b359c..2c009e772e 100644
--- a/src/Service.Tests/Mcp/ReadRecordsToolMsSqlIntegrationTests.cs
+++ b/src/Service.Tests/Mcp/ReadRecordsToolMsSqlIntegrationTests.cs
@@ -61,6 +61,39 @@ public async Task ReadRecords_WithSelect_ReturnsSelectedFields()
             Assert.IsTrue(firstRecord.TryGetProperty("title", out _), "Expected 'title' field in result.");
         }
 
+        /// <summary>
+        /// Reads records with whitespace after a comma in the select clause.
+        /// </summary>
+        [TestMethod]
+        public async Task ReadRecords_WithWhitespaceAfterSelectComma_ReturnsSelectedFields()
+        {
+            CallToolResult result = await ExecuteReadAsync("Book", select: "id, title");
+
+            AssertSuccess(result, "ReadRecords with whitespace after a select comma should succeed.");
+
+            JsonElement root = ParseResultRoot(result);
+            JsonElement records = GetRecordsArray(root);
+            JsonElement firstRecord = records[0];
+            Assert.IsTrue(firstRecord.TryGetProperty("id", out _), "Expected 'id' field in result.");
+            Assert.IsTrue(firstRecord.TryGetProperty("title", out _), "Expected 'title' field in result.");
+        }
+
+        /// <summary>
+        /// Rejects empty field names in the select clause with a clear error.
+        /// </summary>
+        [DataTestMethod]
+        [DataRow("id,title,")]
+        [DataRow("id,,title")]
+        public async Task ReadRecords_WithEmptySelectField_ReturnsInvalidArguments(string select)
+        {
+            CallToolResult result = await ExecuteReadAsync("Book", select: select);
+
+            AssertError(result);
+            JsonElement error = ParseResultRoot(result).GetProperty("error");
+            Assert.AreEqual("InvalidArguments", error.GetProperty("type").GetString());
+            Assert.AreEqual("The 'select' argument cannot contain empty field names.", error.GetProperty("message").GetString());
+        }
+
         /// <summary>
         /// Reads records with an OData filter expression and verifies filtered results are returned.
         /// </summary>