CSHARP-5750: Add support for new QE prefix/substring/suffix aggregation expression operators by papafe · Pull Request #2003 · mongodb/mongo-csharp-driver

papafe · 2026-05-19T13:45:59Z

No description provided.

Copilot

Pull request overview

Adds LINQ3 + filter builder support for Queryable Encryption (QE) encrypted-string aggregation expression operators ($encStrStartsWith, $encStrContains, $encStrEndsWith, $encStrNormalizedEq) so they can be emitted from driver APIs and rendered into correct aggregation AST / $expr filters.

Changes:

Introduces a new LINQ3 AST expression (AstEncStrExpression) and operator enum (AstEncStrOperator) with rendering support.
Adds LINQ3 translation + serializer deduction for the new Mql.EncStr* methods.
Adds FilterDefinitionBuilder helpers (EncStr*) that render $expr filters, plus unit tests for both LINQ and filter builder output.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tests/MongoDB.Driver.Tests/Linq/Linq3Implementation/Translators/ExpressionToAggregationExpressionTranslators/MethodTranslators/EncStrMethodToAggregationExpressionTranslatorTests.cs	New unit tests asserting correct AST for `Mql.EncStr*` translations.
tests/MongoDB.Driver.Tests/FilterDefinitionBuilderTests.cs	Adds tests for new `FilterDefinitionBuilder.EncStr` helpers rendering `$expr` + `$encStr`.
src/MongoDB.Driver/Mql.cs	Adds public `Mql.EncStr*` extension-style methods for LINQ translation.
src/MongoDB.Driver/Linq/Linq3Implementation/Translators/ExpressionToAggregationExpressionTranslators/MethodTranslators/EncStrMethodToAggregationExpressionTranslator.cs	New translator mapping `Mql.EncStr*` calls to an `AstEncStrExpression`.
src/MongoDB.Driver/Linq/Linq3Implementation/Translators/ExpressionToAggregationExpressionTranslators/MethodCallExpressionToAggregationExpressionTranslator.cs	Routes `EncStr*` method calls to the new translator.
src/MongoDB.Driver/Linq/Linq3Implementation/SerializerFinders/SerializerFinderVisitMethodCall.cs	Deduces serializers for `EncStr*` method calls (inputs and boolean return).
src/MongoDB.Driver/Linq/Linq3Implementation/Reflection/MqlMethod.cs	Registers `Mql.EncStr*` method infos and overload set for translation/deduction.
src/MongoDB.Driver/Linq/Linq3Implementation/Ast/Visitors/AstNodeVisitor.cs	Adds visitor support for traversing `AstEncStrExpression`.
src/MongoDB.Driver/Linq/Linq3Implementation/Ast/Expressions/AstExpression.cs	Adds factory method `EncStrExpression(...)`.
src/MongoDB.Driver/Linq/Linq3Implementation/Ast/Expressions/AstEncStrOperator.cs	New enum + rendering helpers for `$encStr*` operator names and value-arg key.
src/MongoDB.Driver/Linq/Linq3Implementation/Ast/Expressions/AstEncStrExpression.cs	New AST node that renders `{ $encStrX: { input, <substring/prefix/...>: value } }`.
src/MongoDB.Driver/Linq/Linq3Implementation/Ast/AstNodeType.cs	Adds `EncStrExpression` node type.
src/MongoDB.Driver/FilterDefinitionBuilder.cs	Adds `FilterDefinitionBuilder.EncStr*` helpers and internal `$expr`-rendering filter definition.

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

+            if (method.IsOneOf(MqlMethod.EncStrMethodOverloads))
+            {
+                var inputTranslation = ExpressionToAggregationExpressionTranslator.Translate(context, arguments[0]);
+                var valueTranslation = ExpressionToAggregationExpressionTranslator.Translate(context, arguments[1]);
+
+                var @operator = method.Name switch
+                {
+                    "EncStrContains" => AstEncStrOperator.Contains,
+                    "EncStrEndsWith" => AstEncStrOperator.EndsWith,
+                    "EncStrNormalizedEq" => AstEncStrOperator.NormalizedEq,
+                    "EncStrStartsWith" => AstEncStrOperator.StartsWith,
+                    _ => throw new InvalidOperationException($"Unexpected method: {method.Name}")
+                };
+
+                var ast = AstExpression.EncStrExpression(@operator, inputTranslation.Ast, valueTranslation.Ast);
+                return new TranslatedExpression(expression, ast, BooleanSerializer.Instance);


ajcvickers · 2026-05-27T13:19:51Z


        void DeduceMethodCallSerializers()
        {
            switch (node.Method.Name)


This switch seems dubious to me since it only matches by method name, and hence might be operating on some arbitrary method which has the same name as the one we expect, but is not the method we expect.

It's true that here we just check by name, but then inside the various Deduce... methods we check if it's the correct one with method.IsOneOf(MqlMethod.EncStrMethodOverloads) for instance.

Yep, we have PR to switch on MethodInfo instead, which is blocked for now, but I hope will be unblocked and merged soon.

ajcvickers · 2026-05-27T13:21:30Z

+
+namespace MongoDB.Driver.Linq.Linq3Implementation.Ast.Expressions;
+
+internal sealed class AstEncStrExpression : AstExpression


Consider using expression bodies for methods.

ajcvickers · 2026-05-27T13:22:30Z

+
+namespace MongoDB.Driver.Tests.Linq.Linq3Implementation.Translators.ExpressionToAggregationExpressionTranslators.MethodTranslators;
+
+public class EncStrMethodToAggregationExpressionTranslatorTests


Looks like we have no end-to-end testing for these operators.

We do not. Actually in general the only end-to-end tests for QE are the ones coming from specs, both prose and unified tests.

I think we should have some, at least for happy-path.

I feel we need to add end-to-end testing here. This is something I feel we need to do more of in general.

ajcvickers · 2026-05-27T13:24:03Z

        /// <param name="representaion">The representation.</param>
        /// <typeparam name="TValue">The type of the value.</typeparam>
        /// <returns>The value</returns>
        public static TValue Constant<TValue>(TValue value, BsonType representaion)


Unfortunately this is in the public API, so we should fix it for 4.0

ajcvickers · 2026-05-27T13:26:33Z

+                var valueExpression = arguments[1];
+                if (IsNotKnown(inputExpression))
+                {
+                    AddNodeSerializer(inputExpression, StringSerializer.Instance);


Is the string serializer correct here? Could these be encrypted fields that require something else? Do we have tests for this?

Yes it should be, QE-encrypted values must be strings.
Regarding tests... It depends what you mean?

sanych-sun · 2026-06-04T23:50:03Z

+                var inputTranslation = ExpressionToAggregationExpressionTranslator.Translate(context, arguments[0]);
+                var valueTranslation = ExpressionToAggregationExpressionTranslator.Translate(context, arguments[1]);
+                if (valueTranslation.Serializer is IRepresentationConfigurable representationConfigurable &&
+                    representationConfigurable.Representation != BsonType.String)


As far as I understood (but do not take it as a true without validating, I need to learn more about encryption in MongoDB) encrypted data could be stored either as base64 string or as BinaryData. Should we support BinaryData representation here as well?

sanych-sun · 2026-06-04T23:55:04Z

+
+            if (method.IsOneOf(MqlMethod.EncStrMethodOverloads))
+            {
+                var inputTranslation = ExpressionToAggregationExpressionTranslator.Translate(context, arguments[0]);


Do we need to validate representation for the input parameter too?

…on expression operators

…odies, serializer tests - Reject non-string value representation in EncStr translator (with negative test) - Use expression bodies in AstEncStrExpression - Add EncStr cases to SerializerFinder MqlTests

papafe added the feature Adds new user-facing functionality. label May 19, 2026

papafe marked this pull request as ready for review May 27, 2026 11:13

papafe requested a review from a team as a code owner May 27, 2026 11:13

papafe requested review from ajcvickers and Copilot May 27, 2026 11:13

Copilot started reviewing on behalf of papafe May 27, 2026 11:13 View session

Copilot AI reviewed May 27, 2026

View reviewed changes

ajcvickers reviewed May 27, 2026

View reviewed changes

ajcvickers requested changes May 27, 2026

View reviewed changes

papafe requested a review from ajcvickers June 2, 2026 16:33

sanych-sun reviewed Jun 4, 2026

View reviewed changes

papafe added 7 commits June 8, 2026 18:17

CSHARP-5750: Add support for new QE prefix/substring/suffix aggregati…

f21d449

…on expression operators

Added LINQ support

e8c3c27

Small correction

9d11cb5

File scoped namespace.

8bb20b0

Small improvements

3cab2d0

Added small test

07c20a8

Address review feedback: validate value arg is a string, expression b…

9fa66d4

…odies, serializer tests - Reject non-string value representation in EncStr translator (with negative test) - Use expression bodies in AstEncStrExpression - Add EncStr cases to SerializerFinder MqlTests

papafe force-pushed the csharp5750 branch from 6c2795c to aa1f9fa Compare June 8, 2026 16:23

Validate input arg is a string; add QE text query integration tests

d9e0065

papafe force-pushed the csharp5750 branch from aa1f9fa to d9e0065 Compare June 8, 2026 20:12


		namespace MongoDB.Driver.Linq.Linq3Implementation.Ast.Expressions;

		internal sealed class AstEncStrExpression : AstExpression


		namespace MongoDB.Driver.Tests.Linq.Linq3Implementation.Translators.ExpressionToAggregationExpressionTranslators.MethodTranslators;

		public class EncStrMethodToAggregationExpressionTranslatorTests

Conversation

papafe commented May 19, 2026

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Reviewed changes

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

4 participants