Fix: URL-encoded special characters in $filter and $orderby break OData parsing

src/Core/Models/RestRequestContexts/RestRequestContext.cs

@@ -77,6 +77,12 @@ protected RestRequestContext(string entityName, DatabaseObject dbo)
     /// </summary>
     public NameValueCollection ParsedQueryString { get; set; } = new();
 
+    /// <summary>
+    /// Raw query string from the HTTP request (URL-encoded).
+    /// Used to preserve encoding for special characters in query parameters.
+    /// </summary>
+    public string RawQueryString { get; set; } = string.Empty;
+
     /// <summary>
     /// String holds information needed for pagination.
     /// Based on request this property may or may not be populated.

src/Core/Parsers/RequestParser.cs

@@ -113,14 +113,16 @@ public static void ParseQueryString(RestRequestContext context, ISqlMetadataProv
                         context.FieldsToBeReturned = context.ParsedQueryString[key]!.Split(",").ToList();
                         break;
                     case FILTER_URL:
-                        // save the AST that represents the filter for the query
-                        // ?$filter=<filter clause using microsoft api guidelines>
-                        string filterQueryString = $"?{FILTER_URL}={context.ParsedQueryString[key]}";
-                        context.FilterClauseInUrl = sqlMetadataProvider.GetODataParser().GetFilterClause(filterQueryString, $"{context.EntityName}.{context.DatabaseObject.FullName}");
+                        // Use raw (URL-encoded) filter value to preserve special characters like &
+                        string? rawFilterValue = ExtractRawQueryParameter(context.RawQueryString, FILTER_URL);
+                        if (rawFilterValue is not null)
+                            context.FilterClauseInUrl = sqlMetadataProvider.GetODataParser().GetFilterClause($"?{FILTER_URL}={rawFilterValue}", $"{context.EntityName}.{context.DatabaseObject.FullName}");
                         break;
                     case SORT_URL:
-                        string sortQueryString = $"?{SORT_URL}={context.ParsedQueryString[key]}";
-                        (context.OrderByClauseInUrl, context.OrderByClauseOfBackingColumns) = GenerateOrderByLists(context, sqlMetadataProvider, sortQueryString);
+                        // Use raw (URL-encoded) orderby value to preserve special characters
+                        string? rawSortValue = ExtractRawQueryParameter(context.RawQueryString, SORT_URL);
+                        if (rawSortValue is not null)
+                            (context.OrderByClauseInUrl, context.OrderByClauseOfBackingColumns) = GenerateOrderByLists(context, sqlMetadataProvider, $"?{SORT_URL}={rawSortValue}");
                         break;
                     case AFTER_URL:
                         context.After = context.ParsedQueryString[key];
@@ -283,5 +285,22 @@ private static bool IsNull(string value)
         {
             return string.IsNullOrWhiteSpace(value) || string.Equals(value, "null", StringComparison.OrdinalIgnoreCase);
         }
+
+        /// <summary>
+        /// Extracts the raw (URL-encoded) value of a query parameter from a query string.
+        /// Preserves special characters like & in filter values (e.g., %26 stays as %26).
+        /// </summary>
+        private static string? ExtractRawQueryParameter(string queryString, string parameterName)
+        {
+            if (string.IsNullOrWhiteSpace(queryString)) return null;
+
+            foreach (string param in queryString.TrimStart('?').Split('&'))
+            {
+                int idx = param.IndexOf('=');
+                if (idx >= 0 && param.Substring(0, idx).Equals(parameterName, StringComparison.OrdinalIgnoreCase))
+                    return idx < param.Length - 1 ? param.Substring(idx + 1) : string.Empty;
+            }
+            return null;
+        }
     }
 }

src/Core/Services/RestService.cs

@@ -174,6 +174,7 @@ RequestValidator requestValidator
 
                 if (!string.IsNullOrWhiteSpace(queryString))
                 {
+                    context.RawQueryString = queryString;
                     context.ParsedQueryString = HttpUtility.ParseQueryString(queryString);
                     RequestParser.ParseQueryString(context, sqlMetadataProvider);
                 }
@@ -277,6 +278,7 @@ private void PopulateStoredProcedureContext(
                     // So, $filter will be treated as any other parameter (inevitably will raise a Bad Request)
                     if (!string.IsNullOrWhiteSpace(queryString))
                     {
+                        context.RawQueryString = queryString;
                         context.ParsedQueryString = HttpUtility.ParseQueryString(queryString);
                     }
 

src/Service.Tests/DatabaseSchema-DwSql.sql

@@ -337,7 +337,8 @@ VALUES (1, 'Awesome book', 1234),
 (18, '[Special Book]', 1234),
 (19, 'ME\YOU', 1234),
 (20, 'C:\\LIFE', 1234),
-(21, '', 1234);
+(21, '', 1234),
+(22, 'filter & test', 1234);
 
 INSERT INTO book_website_placements(id, book_id, price) VALUES (1, 1, 100), (2, 2, 50), (3, 3, 23), (4, 5, 33);
 

src/Service.Tests/DatabaseSchema-MsSql.sql

@@ -532,7 +532,8 @@ VALUES (1, 'Awesome book', 1234),
 (18, '[Special Book]', 1234),
 (19, 'ME\YOU', 1234),
 (20, 'C:\\LIFE', 1234),
-(21, '', 1234);
+(21, '', 1234),
+(22, 'filter & test', 1234);
 SET IDENTITY_INSERT books OFF
 
 SET IDENTITY_INSERT books_mm ON

src/Service.Tests/DatabaseSchema-MySql.sql

@@ -389,7 +389,8 @@ INSERT INTO books(id, title, publisher_id)
         (18, '[Special Book]', 1234),
         (19, 'ME\\YOU', 1234),
         (20, 'C:\\\\LIFE', 1234),
-        (21, '', 1234);
+        (21, '', 1234),
+        (22, 'filter & test', 1234);
 INSERT INTO book_website_placements(book_id, price) VALUES (1, 100), (2, 50), (3, 23), (5, 33);
 INSERT INTO website_users(id, username) VALUES (1, 'George'), (2, NULL), (3, ''), (4, 'book_lover_95'), (5, 'null');
 INSERT INTO book_author_link(book_id, author_id) VALUES (1, 123), (2, 124), (3, 123), (3, 124), (4, 123), (4, 124), (5, 126);

src/Service.Tests/DatabaseSchema-PostgreSql.sql

@@ -392,7 +392,8 @@ INSERT INTO books(id, title, publisher_id)
         (18, '[Special Book]', 1234),
         (19, 'ME\YOU', 1234),
         (20, 'C:\\LIFE', 1234),
-        (21, '', 1234);
+        (21, '', 1234),
+        (22, 'filter & test', 1234);
 INSERT INTO book_website_placements(book_id, price) VALUES (1, 100), (2, 50), (3, 23), (5, 33);
 INSERT INTO website_users(id, username) VALUES (1, 'George'), (2, NULL), (3, ''), (4, 'book_lover_95'), (5, 'null');
 INSERT INTO book_author_link(book_id, author_id) VALUES (1, 123), (2, 124), (3, 123), (3, 124), (4, 123), (4, 124), (5, 126);;

src/Service.Tests/SqlTests/RestApiTests/Find/DwSqlFindApiTests.cs

@@ -221,6 +221,12 @@ public class DwSqlFindApiTests : FindApiTestBase
                 $"WHERE (NOT (id < 3) OR id < 4) OR NOT (title = 'Awesome book') " +
                 $"FOR JSON PATH, INCLUDE_NULL_VALUES"
             },
+            {
+                "FindTestWithFilterContainingSpecialCharacters",
+                $"SELECT * FROM { _integrationTableName } " +
+                $"WHERE title = 'filter & test' " +
+                $"FOR JSON PATH, INCLUDE_NULL_VALUES"
+            },
             {
                 "FindTestWithPrimaryKeyContainingForeignKey",
                 $"SELECT [id], [content] FROM reviews " +

src/Service.Tests/SqlTests/RestApiTests/Find/FindApiTestBase.cs

@@ -693,6 +693,22 @@ await SetupAndRunRestApiTest(
             );
         }
 
+        /// <summary>
+        /// Tests the REST Api for Find operation with a filter containing special characters
+        /// like ampersand (&) that need to be URL-encoded. This validates that the fix for
+        /// the double-decoding issue is working correctly.
+        /// </summary>
+        [TestMethod]
+        public async Task FindTestWithFilterContainingSpecialCharacters()
+        {
+            await SetupAndRunRestApiTest(
+                primaryKeyRoute: string.Empty,
+                queryString: "?$filter=title eq 'filter & test'",
+                entityNameOrPath: _integrationEntityName,
+                sqlQuery: GetQuery(nameof(FindTestWithFilterContainingSpecialCharacters))
+            );
+        }
+
         /// <summary>
         /// Tests the REST Api for Find operation where we compare one field
         /// to the bool returned from another comparison.

src/Service.Tests/SqlTests/RestApiTests/Find/MsSqlFindApiTests.cs

@@ -228,6 +228,12 @@ public class MsSqlFindApiTests : FindApiTestBase
                 $"WHERE (NOT (id < 3) OR id < 4) OR NOT (title = 'Awesome book') " +
                 $"FOR JSON PATH, INCLUDE_NULL_VALUES"
             },
+            {
+                "FindTestWithFilterContainingSpecialCharacters",
+                $"SELECT * FROM { _integrationTableName } " +
+                $"WHERE title = 'filter & test' " +
+                $"FOR JSON PATH, INCLUDE_NULL_VALUES"
+            },
             {
                 "FindTestWithPrimaryKeyContainingForeignKey",
                 $"SELECT [id], [content] FROM reviews " +

src/Service.Tests/SqlTests/RestApiTests/Find/MySqlFindApiTests.cs

@@ -397,6 +397,18 @@ ORDER BY id asc
                     ) AS subq
                 "
             },
+            {
+                "FindTestWithFilterContainingSpecialCharacters",
+                @"
+                    SELECT JSON_ARRAYAGG(JSON_OBJECT('id', id, 'title', title, 'publisher_id', publisher_id)) AS data
+                    FROM (
+                        SELECT *
+                        FROM " + _integrationTableName + @"
+                        WHERE title = 'filter & test'
+                        ORDER BY id asc
+                    ) AS subq
+                "
+            },
             {
                 "FindTestWithFilterQueryStringBoolResultFilter",
                 @"

src/Service.Tests/SqlTests/RestApiTests/Find/PostgreSqlFindApiTests.cs

@@ -411,6 +411,17 @@ SELECT json_agg(to_jsonb(subq)) AS data
                       ORDER BY id asc
                   ) AS subq"
             },
+            {
+                "FindTestWithFilterContainingSpecialCharacters",
+                @"
+                  SELECT json_agg(to_jsonb(subq)) AS data
+                  FROM (
+                      SELECT *
+                      FROM " + _integrationTableName + @"
+                      WHERE title = 'filter & test'
+                      ORDER BY id asc
+                  ) AS subq"
+            },
             {
                 "FindTestWithPrimaryKeyContainingForeignKey",
                 @"

src/Service.Tests/UnitTests/RequestParserUnitTests.cs

@@ -0,0 +1,90 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+using System.Reflection;
+using Azure.DataApiBuilder.Core.Parsers;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace Azure.DataApiBuilder.Service.Tests.UnitTests
+{
+    /// <summary>
+    /// Test class for RequestParser utility methods.
+    /// Specifically tests the ExtractRawQueryParameter method which preserves
+    /// URL encoding for special characters in query parameters.
+    /// </summary>
+    [TestClass]
+    public class RequestParserUnitTests
+    {
+        /// <summary>
+        /// Tests that ExtractRawQueryParameter correctly extracts URL-encoded
+        /// parameter values, preserving special characters like ampersand (&).
+        /// </summary>
+        [DataTestMethod]
+        [DataRow("?$filter=region%20eq%20%27filter%20%26%20test%27", "$filter", "region%20eq%20%27filter%20%26%20test%27", DisplayName = "Extract filter with encoded ampersand")]
+        [DataRow("?$filter=title%20eq%20%27A%20%26%20B%27&$select=id", "$filter", "title%20eq%20%27A%20%26%20B%27", DisplayName = "Extract filter with ampersand and other params")]
+        [DataRow("?$select=id&$filter=name%20eq%20%27test%27", "$filter", "name%20eq%20%27test%27", DisplayName = "Extract filter when not first parameter")]
+        [DataRow("?$orderby=name%20asc", "$orderby", "name%20asc", DisplayName = "Extract orderby parameter")]
+        [DataRow("?param1=value1&param2=value%26with%26ampersands", "param2", "value%26with%26ampersands", DisplayName = "Extract parameter with multiple ampersands")]
+        [DataRow("$filter=title%20eq%20%27test%27", "$filter", "title%20eq%20%27test%27", DisplayName = "Extract without leading question mark")]
+        [DataRow("?$filter=", "$filter", "", DisplayName = "Extract empty filter value")]
+        public void ExtractRawQueryParameter_PreservesEncoding(string queryString, string parameterName, string expectedValue)
+        {
+            // Use reflection to call the private static method
+            MethodInfo? method = typeof(RequestParser).GetMethod(
+                "ExtractRawQueryParameter",
+                BindingFlags.NonPublic | BindingFlags.Static);
+
+            Assert.IsNotNull(method, "ExtractRawQueryParameter method should exist");
+
+            string? result = (string?)method.Invoke(null, new object[] { queryString, parameterName });
+
+            Assert.AreEqual(expectedValue, result, 
+                $"Expected '{expectedValue}' but got '{result}' for parameter '{parameterName}' in query '{queryString}'");
+        }
+
+        /// <summary>
+        /// Tests that ExtractRawQueryParameter returns null when parameter is not found.
+        /// </summary>
+        [DataTestMethod]
+        [DataRow("?$filter=test", "$orderby", DisplayName = "Parameter not in query string")]
+        [DataRow("", "$filter", DisplayName = "Empty query string")]
+        [DataRow(null, "$filter", DisplayName = "Null query string")]
+        [DataRow("?otherParam=value", "$filter", DisplayName = "Different parameter")]
+        public void ExtractRawQueryParameter_ReturnsNull_WhenParameterNotFound(string? queryString, string parameterName)
+        {
+            // Use reflection to call the private static method
+            MethodInfo? method = typeof(RequestParser).GetMethod(
+                "ExtractRawQueryParameter",
+                BindingFlags.NonPublic | BindingFlags.Static);
+
+            Assert.IsNotNull(method, "ExtractRawQueryParameter method should exist");
+
+            string? result = (string?)method.Invoke(null, new object?[] { queryString, parameterName });
+
+            Assert.IsNull(result, 
+                $"Expected null but got '{result}' for parameter '{parameterName}' in query '{queryString}'");
+        }
+
+        /// <summary>
+        /// Tests that ExtractRawQueryParameter handles edge cases correctly.
+        /// </summary>
+        [DataTestMethod]
+        [DataRow("?$filter=value&$filter=anothervalue", "$filter", "value", DisplayName = "Multiple same parameters - returns first")]
+        [DataRow("?$FILTER=value", "$filter", "value", DisplayName = "Case insensitive parameter matching")]
+        [DataRow("?param=value1&value2", "param", "value1", DisplayName = "Value with unencoded ampersand after parameter")]
+        public void ExtractRawQueryParameter_HandlesEdgeCases(string queryString, string parameterName, string expectedValue)
+        {
+            // Use reflection to call the private static method
+            MethodInfo? method = typeof(RequestParser).GetMethod(
+                "ExtractRawQueryParameter",
+                BindingFlags.NonPublic | BindingFlags.Static);
+
+            Assert.IsNotNull(method, "ExtractRawQueryParameter method should exist");
+
+            string? result = (string?)method.Invoke(null, new object[] { queryString, parameterName });
+
+            Assert.AreEqual(expectedValue, result, 
+                $"Expected '{expectedValue}' but got '{result}' for parameter '{parameterName}' in query '{queryString}'");
+        }
+    }
+}