CSHARP-5473: Provide API to turn LINQ expression into MQL #1601

rstam · 2025-01-25T21:15:43Z

The BIG question for this PR is whether we want to do this at all, and if so what the public API should be.

sanych-sun · 2025-01-29T18:18:24Z

tests/MongoDB.Driver.Tests/Linq/Linq3Implementation/Jira/CSharp5473Tests.cs

+    public class CSharp5473Tests : Linq3IntegrationTest
+    {
+        [Fact]
+        public void Select_decimal_divide_should_work()


Minor : Test method name seems to be wrong.

sanych-sun · 2025-01-29T18:20:44Z

tests/MongoDB.Driver.Tests/Linq/Linq3Implementation/Jira/CSharp5473Tests.cs

+            var stages = provider.Translate(queryable, out var outputSerializer);
+            AssertStages(stages, "{ $project : { _v : { $add : ['$X', 1] }, _id : 0 } }");
+
+            var result = queryable.First();


Should we try to execute translated MQL in some way instead to make sure the translation was done properly?

Yes, but not necessarily to verify that the translation was done correctly.

I'm more interested in showing HOW you could execute the result of Translate.

sanych-sun

LGTM + minor question.

sanych-sun · 2025-02-03T17:37:00Z

src/MongoDB.Driver/Linq/Linq3Implementation/MongoQueryProvider.cs

            return translationOptions.AddMissingOptionsFrom(database?.Client.Settings.TranslationOptions);
        }
+
+        public override BsonDocument[] Translate<TResult>(IQueryable<TResult> queryable, out IBsonSerializer<TResult> outputSerializer)


Should we check if provided queryable is MongoDB queryable?

Or maybe receiving an expression is sufficient?

It would be sufficient.

I chose IQueryable to emphasize that it's the Expression associated with an IQueryable that is being translated, not any old expression.

But the .NET method takes an Expression, so we could also here.

@damieng what do you think?

The translate method seems to only care about the expression of the queryable so I think we should just take Expression here as well. We can add a note in the comments of methods to emphasize the expression should be associated with an IQueryable and maybe throw an exception if we catch such as a case?

damieng · 2025-02-03T20:42:33Z

I think if we want to ship this for now we should use the [Experimental] attribute.

Alternatively I could use reflection to do the same sort of thing on the already-released version and make sure it meets our use cases on the EF provider before shipping.

rstam · 2025-02-03T23:36:42Z

I think if we want to ship this for now we should use the [Experimental] attribute.

Alternatively I could use reflection to do the same sort of thing on the already-released version and make sure it meets our use cases on the EF provider before shipping.

You are the one that asked for this. If you are not sure it does what you need then we shouldn't ship it yet.

BorisDog

LGTM

rstam · 2025-04-03T17:50:59Z

src/MongoDB.Driver/Linq/IMongoQueryProvider.cs

+        /// <param name="outputSerializer">The output serializer.</param>
+        /// <typeparam name="TResult">The type of the result.</typeparam>
+        /// <returns>An array of MQL pipeline stages represented as BsonDocuments.</returns>
+        BsonDocument[] Translate<TResult>(Expression expression, out IBsonSerializer<TResult> outputSerializer);


Adelin commented:

The translate method seems to only care about the expression of the queryable so I think we should just take Expression here as well.

The latest commit implements his suggestion.

@BorisDog and @damieng will this work for you two in the Analyzer and the EF Core Provider?

I think receiving expression is more consistent with ExecuteAsync.
Analyzer will not use this functionality at all.

BorisDog

If this is still needed for EF, LGTM.

…dummy queryable.

…instead of an IQueryable.

rstam · 2025-11-10T15:17:13Z

Rebase on main.

Copilot

Pull Request Overview

This PR introduces a public API to translate LINQ expressions into MongoDB Query Language (MQL) pipeline stages. The implementation adds a Translate method to the IMongoQueryProvider interface that converts a LINQ expression into an array of BsonDocument stages along with the appropriate output serializer.

Key Changes:

Added Translate<TResult> method to IMongoQueryProvider interface and its implementations
Implemented translation logic in MongoQueryProvider<TDocument> that leverages existing internal translation infrastructure
Added comprehensive test coverage demonstrating the translation of a simple projection expression

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/MongoDB.Driver/Linq/IMongoQueryProvider.cs	Adds public API method signature with XML documentation for translating expressions to MQL
src/MongoDB.Driver/Linq/Linq3Implementation/MongoQueryProvider.cs	Implements the translation method in both abstract base class and concrete provider, using existing translation infrastructure
tests/MongoDB.Driver.Tests/Linq/Linq3Implementation/Jira/CSharp5473Tests.cs	Adds test validating the new translation API with a projection example

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

Copilot · 2025-11-10T17:04:16Z

src/MongoDB.Driver/Linq/Linq3Implementation/MongoQueryProvider.cs

+            var executableQuery = ExpressionToExecutableQueryTranslator.Translate<TDocument, TResult>(provider: this, expression, translationOptions);
+            var stages = executableQuery.Pipeline.Ast.Stages;
+            outputSerializer = (IBsonSerializer<TResult>)executableQuery.Pipeline.OutputSerializer;
+            return stages.Select(s => s.Render().AsBsonDocument).ToArray();


The Select().ToArray() pattern creates an intermediate enumerable before materializing the array. Consider using a for loop or Array.ConvertAll for better performance, especially if the stages collection could be large.

Suggested change

return stages.Select(s => s.Render().AsBsonDocument).ToArray();

var result = new BsonDocument[stages.Count];

for (int i = 0; i < stages.Count; i++)

{

result[i] = stages[i].Render().AsBsonDocument;

}

return result;

rstam requested review from BorisDog, JamesKovacs, adelinowona, damieng and sanych-sun January 25, 2025 21:15

rstam requested a review from a team as a code owner January 25, 2025 21:15

sanych-sun requested changes Jan 29, 2025

View reviewed changes

rstam requested a review from sanych-sun January 29, 2025 22:55

sanych-sun previously approved these changes Feb 3, 2025

View reviewed changes

BorisDog approved these changes Mar 21, 2025

View reviewed changes

rstam force-pushed the csharp5473 branch from b838f79 to 2ce7508 Compare April 3, 2025 17:49

rstam commented Apr 3, 2025

View reviewed changes

rstam requested review from BorisDog and sanych-sun April 3, 2025 17:51

BorisDog approved these changes Apr 4, 2025

View reviewed changes

sanych-sun added the feature Adds new user-facing functionality. label Apr 10, 2025

rstam marked this pull request as draft April 11, 2025 21:20

rstam dismissed sanych-sun’s stale review via 2ce7508 July 17, 2025 21:57

rstam added 4 commits November 10, 2025 10:14

CSHARP-5473: Provide API to turn LINQ expression into MQL.

b0aca82

CSHARP-5473: Requested changes.

d966e77

CSHARP-5473: Add test showing how to translate an Expression using a …

7eeeb63

…dummy queryable.

CSHARP-5473: Change Translate method to have an Expression parameter …

dacdf29

…instead of an IQueryable.

rstam force-pushed the csharp5473 branch from 2ce7508 to dacdf29 Compare November 10, 2025 15:16

rstam changed the title ~~CSHARP-5473: Provide API to turn LINQ expression into MQL.~~ CSHARP-5473: Provide API to turn LINQ expression into MQL Nov 10, 2025

adelinowona requested a review from Copilot November 10, 2025 17:03

Copilot AI reviewed Nov 10, 2025

View reviewed changes

-            return stages.Select(s => s.Render().AsBsonDocument).ToArray();
+            var result = new BsonDocument[stages.Count];
+            for (int i = 0; i < stages.Count; i++)
+            {
+                result[i] = stages[i].Render().AsBsonDocument;
+            }
+            return result;

CSHARP-5473: Provide API to turn LINQ expression into MQL #1601

Are you sure you want to change the base?

CSHARP-5473: Provide API to turn LINQ expression into MQL #1601

Conversation

rstam commented Jan 25, 2025

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 left a comment

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!

damieng commented Feb 3, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

rstam commented Feb 3, 2025

Uh oh!

BorisDog left a comment

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!

BorisDog left a comment

Choose a reason for hiding this comment

Uh oh!

rstam commented Nov 10, 2025

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull Request Overview

Reviewed Changes

Uh oh!

Copilot AI Nov 10, 2025

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

5 participants

damieng commented Feb 3, 2025 •

edited

Loading