CSHARP-5825: Support (de)serialization between BSON and EJSON by papafe · Pull Request #1939 · mongodb/mongo-csharp-driver

papafe · 2026-04-07T08:39:27Z

No description provided.

adelinowona · 2026-04-09T22:39:04Z

The new methods in this file break the alphabetical ordering.

adelinowona · 2026-04-09T22:40:08Z

+        DeserializeEJsonExpression,
        DateAddExpression,


nit: DateAddExpression should come before DeserializeEJsonExpression.

adelinowona · 2026-04-09T22:41:44Z

+        private static readonly MethodInfo __deserializeEJson;
        private static readonly MethodInfo __dateFromStringWithFormat;


__dateFromStringWithFormat (and the other __dateFromString* variants) should all appear before __deserializeEJson .

Same issue in the public properties section (lines 113-117): DeserializeEJson is wedged between DateFromString and DateFromStringWithFormat*.

adelinowona · 2026-04-10T19:01:28Z

+        private bool? _relaxed;
+
+        /// <summary>
+        /// The relaxed parameter. When true, produces relaxed Extended JSON format. When false, produces canonical format. Defaults to true.


The sentence "Defaults to true" could be misread as "this C# property defaults to true." The property defaults to null (not set). The server defaults to true when the parameter is omitted. I would suggest clarifying: "The server defaults to true when this is not specified."

papafe · 2026-04-13T13:21:38Z

@adelinowona I agree with all your comments, fixed.

Copilot

Pull request overview

Adds LINQ3/MQL support for Extended JSON v2 (EJSON) round-tripping by introducing $serializeEJSON and $deserializeEJSON operators, including public Mql APIs, AST nodes, translators, and both unit + integration tests.

Changes:

Introduce Mql.SerializeEJson / Mql.DeserializeEJson APIs and corresponding options types.
Implement LINQ3 translation + AST rendering for $serializeEJSON and $deserializeEJSON.
Add translator unit tests and server-gated integration tests for both operators.

Reviewed changes

Copilot reviewed 18 out of 18 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
tests/MongoDB.Driver.Tests/Linq/Linq3Implementation/Translators/ExpressionToAggregationExpressionTranslators/MethodTranslators/SerializeEJsonMethodToAggregationExpressionTranslatorTests.cs	Adds unit tests asserting correct AST for `$serializeEJSON` translation/options.
tests/MongoDB.Driver.Tests/Linq/Linq3Implementation/Translators/ExpressionToAggregationExpressionTranslators/MethodTranslators/DeserializeEJsonMethodToAggregationExpressionTranslatorTests.cs	Adds unit tests asserting correct AST for `$deserializeEJSON` translation/options.
tests/MongoDB.Driver.Tests/Linq/Integration/MqlSerializeEJsonTests.cs	Adds integration tests validating server execution/behavior of `$serializeEJSON`.
tests/MongoDB.Driver.Tests/Linq/Integration/MqlDeserializeEJsonTests.cs	Adds integration tests validating server execution/behavior of `$deserializeEJSON`.
src/MongoDB.Driver/SerializeEJsonOptions.cs	Introduces public options types for serialization (`Relaxed`, `OnError`).
src/MongoDB.Driver/DeserializeEJsonOptions.cs	Introduces public options types for deserialization (`OnError`).
src/MongoDB.Driver/Mql.cs	Adds new public Mql entry points for (de)serializing EJSON.
src/MongoDB.Driver/Linq/Linq3Implementation/Translators/ExpressionToAggregationExpressionTranslators/MethodTranslators/SerializeEJsonMethodToAggregationExpressionTranslator.cs	Implements LINQ3 translation into `$serializeEJSON` AST.
src/MongoDB.Driver/Linq/Linq3Implementation/Translators/ExpressionToAggregationExpressionTranslators/MethodTranslators/DeserializeEJsonMethodToAggregationExpressionTranslator.cs	Implements LINQ3 translation into `$deserializeEJSON` AST.
src/MongoDB.Driver/Linq/Linq3Implementation/Translators/ExpressionToAggregationExpressionTranslators/MethodCallExpressionToAggregationExpressionTranslator.cs	Wires new Mql methods into the method-call translator dispatch.
src/MongoDB.Driver/Linq/Linq3Implementation/SerializerFinders/SerializerFinderVisitMethodCall.cs	Deduces serializers for the new Mql method calls.
src/MongoDB.Driver/Linq/Linq3Implementation/Reflection/MqlMethod.cs	Adds reflection handles for the new Mql methods.
src/MongoDB.Driver/Linq/Linq3Implementation/Ast/Visitors/AstNodeVisitor.cs	Adds visitor support for the new AST node kinds.
src/MongoDB.Driver/Linq/Linq3Implementation/Ast/Expressions/AstSerializeEJsonExpression.cs	New AST node + renderer for `$serializeEJSON`.
src/MongoDB.Driver/Linq/Linq3Implementation/Ast/Expressions/AstDeserializeEJsonExpression.cs	New AST node + renderer for `$deserializeEJSON`.
src/MongoDB.Driver/Linq/Linq3Implementation/Ast/Expressions/AstExpression.cs	Adds factory helpers to create the new AST expression nodes.
src/MongoDB.Driver/Linq/Linq3Implementation/Ast/AstNodeType.cs	Adds new AST node type enum entries.
src/MongoDB.Driver/Core/Misc/Feature.cs	Adds feature flags for gating tests/operator availability by server wire version.

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

Copilot · 2026-04-13T13:26:51Z

+                        var relaxedValue = relaxedExpression.GetConstantValue<bool>(expression);
+                        relaxedAst = AstExpression.Constant(relaxedValue);


In the MemberInit options translation for Relaxed, the code calls GetConstantValue<bool>(...), but SerializeEJsonOptions.Relaxed is bool?. If a user writes new SerializeEJsonOptions<T> { Relaxed = null } (or an expression that evaluates to null), this will fail during translation instead of treating it as “not specified”. Consider reading a bool? constant and only emitting relaxed when it has a value (matching the constant-options path which checks HasValue).

Suggested change

var relaxedValue = relaxedExpression.GetConstantValue<bool>(expression);

relaxedAst = AstExpression.Constant(relaxedValue);

var relaxedValue = relaxedExpression.GetConstantValue<bool?>(expression);

if (relaxedValue.HasValue)

{

relaxedAst = AstExpression.Constant(relaxedValue.Value);

}

Copilot · 2026-04-13T13:26:52Z

+
+    /// <summary>
+    /// Represents the options parameter for <see cref="Mql.DeserializeEJson{TInput, TOutput}(TInput, DeserializeEJsonOptions{TOutput})"/>.
+    /// This class allows to set 'onError'.


The XML doc comment has a grammatical issue: “This class allows to set 'onError'.” should be “This class allows setting 'onError'.” (or similar).

Suggested change

/// This class allows to set 'onError'.

/// This class allows setting 'onError'.

Copilot · 2026-04-13T13:26:52Z

+/* Copyright 2010-present MongoDB Inc.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+* http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/


The Apache license header formatting here is inconsistent with other files in this directory (e.g., AstDateFromStringExpression.cs uses *-prefixed lines). Consider aligning the comment formatting to the standard header style used elsewhere to keep license headers uniform.

Suggested change

/* Copyright 2010-present MongoDB Inc.

*

* Licensed under the Apache License, Version 2.0 (the "License");

* you may not use this file except in compliance with the License.

* You may obtain a copy of the License at

*

* http://www.apache.org/licenses/LICENSE-2.0

*

* Unless required by applicable law or agreed to in writing, software

* distributed under the License is distributed on an "AS IS" BASIS,

* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

* See the License for the specific language governing permissions and

* limitations under the License.

*/

/*

* Copyright 2010-present MongoDB Inc.

*

* Licensed under the Apache License, Version 2.0 (the "License");

* you may not use this file except in compliance with the License.

* You may obtain a copy of the License at

*

* http://www.apache.org/licenses/LICENSE-2.0

*

* Unless required by applicable law or agreed to in writing, software

* distributed under the License is distributed on an "AS IS" BASIS,

* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

* See the License for the specific language governing permissions and

* limitations under the License.

*/

This seems to be incorrect.

Copilot · 2026-04-13T13:26:52Z

+/* Copyright 2010-present MongoDB Inc.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+* http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/


The Apache license header formatting here is inconsistent with other files in this directory (e.g., AstDateFromStringExpression.cs uses *-prefixed lines). Consider aligning the comment formatting to the standard header style used elsewhere to keep license headers uniform.

Suggested change

/* Copyright 2010-present MongoDB Inc.

*

* Licensed under the Apache License, Version 2.0 (the "License");

* you may not use this file except in compliance with the License.

* You may obtain a copy of the License at

*

* http://www.apache.org/licenses/LICENSE-2.0

*

* Unless required by applicable law or agreed to in writing, software

* distributed under the License is distributed on an "AS IS" BASIS,

* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

* See the License for the specific language governing permissions and

* limitations under the License.

*/

/*

* Copyright 2010-present MongoDB Inc.

*

* Licensed under the Apache License, Version 2.0 (the "License");

* you may not use this file except in compliance with the License.

* You may obtain a copy of the License at

*

* http://www.apache.org/licenses/LICENSE-2.0

*

* Unless required by applicable law or agreed to in writing, software

* distributed under the License is distributed on an "AS IS" BASIS,

* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

* See the License for the specific language governing permissions and

* limitations under the License.

*/

…ization between BSON and EJSON

sanych-sun · 2026-04-14T18:10:37Z

+using MongoDB.Driver.Core.Misc;
+using MongoDB.Driver.Linq.Linq3Implementation.Ast.Visitors;
+
+namespace MongoDB.Driver.Linq.Linq3Implementation.Ast.Expressions


Minor: Could be file-scoped namespace.

sanych-sun · 2026-04-14T18:10:59Z

+
+        public override AstNode Accept(AstNodeVisitor visitor)
+        {
+            return visitor.VisitDeserializeEJsonExpression(this);


Minor: Could be expression-body method.

sanych-sun · 2026-04-14T18:24:25Z

+                if (IsNotKnown(node))
+                {
+                    var outputType = method.GetGenericArguments()[1];
+                    var outputSerializer = BsonSerializer.LookupSerializer(outputType);


I think in this case we should not lookup for serializer, as it might resolve a wrong one. We should assign the serializer from the other part of the expression. For example, if we have code like this:

queryable.Select(d => new MyModel(){ Property = Mql.DeserializeEJson(d.StringField)})

We should deduce the serializer from serializer for Property. It might be already handled by VisitMemberInitExpression. Could you please double-check if the current implementation will pick up a custom serializer, if parent document serializer implements IBsonDocumentSerializer?

sanych-sun · 2026-04-14T18:35:29Z

+                if (IsNotKnown(node))
+                {
+                    var outputType = method.GetGenericArguments()[1];
+                    var outputSerializer = BsonSerializer.LookupSerializer(outputType);


Same as above.

sanych-sun · 2026-04-14T18:44:37Z

+        /// <param name="value">The value to deserialize.</param>
+        /// <param name="options">The deserialization options.</param>
+        /// <returns>The deserialized value.</returns>
+        public static TOutput DeserializeEJson<TInput, TOutput>(TInput value, DeserializeEJsonOptions<TOutput> options = null)


Not sure if I dig deep enough, but does runtime type should be the same? Is there any use case when TInput != TOutput?

Yes, it could be for instance <BsonDocument, BsonValue>, <BsonValue, string>

sanych-sun · 2026-04-14T18:53:59Z

Also please add unit tests for serializerFinder. See MongoDB.Driver.Tests.Linq.Linq3Implementation.SerializerFinders.MqlTests.

adelinowona · 2026-04-15T16:36:47Z

+        translation.Ast.Render().Should().Be(BsonDocument.Parse(expectedAst));
+    }
+
+    public static IEnumerable<object[]> SupportedTestCases =


Nit (test coverage): The unit tests cover the MemberInitExpression path (inline new ... { OnError = "fallback" }) and the ConstantExpression path with null. The ConstantExpression path
with a non-null options object (i.e., options created outside the lambda and captured as a closure) isn't directly tested. That path is straightforward — it just reads property values off the object — so this
is minor. Worth noting in case you want to add a case for completeness.

Same for the SerializeEJson translator tests

papafe requested review from Copilot and removed request for Copilot April 7, 2026 08:39

papafe requested a review from a team as a code owner April 7, 2026 08:39

papafe requested a review from adelinowona April 7, 2026 08:39

papafe added the feature Adds new user-facing functionality. label Apr 7, 2026

adelinowona requested changes Apr 10, 2026

View reviewed changes

papafe requested review from adelinowona and Copilot April 13, 2026 13:21

Copilot started reviewing on behalf of papafe April 13, 2026 13:22 View session

Copilot AI reviewed Apr 13, 2026

View reviewed changes

papafe added 7 commits April 13, 2026 16:56

CSHARP-5656: Investigate changes in SERVER-107499: Support (de)serial…

a285da2

…ization between BSON and EJSON

Small fix

6995985

Added small test

24a2d6e

Ordering and comment correction.

d40ed65

Ordering

56582eb

Fixed ordering 2

69eab79

Small fix

f577f29

papafe force-pushed the csharp5825 branch from 525f480 to f577f29 Compare April 13, 2026 14:56

sanych-sun reviewed Apr 14, 2026

View reviewed changes

sanych-sun requested changes Apr 14, 2026

View reviewed changes

adelinowona reviewed Apr 15, 2026

View reviewed changes

		private static readonly MethodInfo __deserializeEJson;
		private static readonly MethodInfo __dateFromStringWithFormat;

		var relaxedValue = relaxedExpression.GetConstantValue<bool>(expression);
		relaxedAst = AstExpression.Constant(relaxedValue);

-                        var relaxedValue = relaxedExpression.GetConstantValue<bool>(expression);
-                        relaxedAst = AstExpression.Constant(relaxedValue);
+                        var relaxedValue = relaxedExpression.GetConstantValue<bool?>(expression);
+                        if (relaxedValue.HasValue)
+                        {
+                            relaxedAst = AstExpression.Constant(relaxedValue.Value);
+                        }

	/// This class allows to set 'onError'.
	/// This class allows setting 'onError'.

Conversation

papafe commented Apr 7, 2026

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!

papafe commented Apr 13, 2026

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Reviewed changes

Uh oh!

Copilot AI Apr 13, 2026

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Copilot AI Apr 13, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Apr 13, 2026

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Copilot AI Apr 13, 2026

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!

sanych-sun commented Apr 14, 2026

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

4 participants