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CSHARP-2187: Flatten CombinedProjectionDefinitions to reduce recursive calls to Render. #1333

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Merged
merged 1 commit into from
May 31, 2024
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CSHARP-2187: Flatten CombinedProjectionDefinitions to reduce recursive calls to Render. #1333

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13 changes: 12 additions & 1 deletion src/MongoDB.Driver/ProjectionDefinitionBuilder.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -789,7 +789,18 @@ internal sealed class CombinedProjectionDefinition<TSource> : ProjectionDefiniti

public CombinedProjectionDefinition(IEnumerable<ProjectionDefinition<TSource>> projections)
{
_projections = Ensure.IsNotNull(projections, nameof(projections)).ToList();
// Unwind CombinedProjectionDefinitions to avoid deep recursion on Render
_projections = Ensure.IsNotNull(projections, nameof(projections))
.Aggregate(new List<ProjectionDefinition<TSource>>(), (current, projection) =>
{
if (projection is CombinedProjectionDefinition<TSource> combinedProjection)
{
current.AddRange(combinedProjection._projections);
} else
current.Add(projection);
return current;
})
.ToList();
}

public override BsonDocument Render(IBsonSerializer<TSource> sourceSerializer, IBsonSerializerRegistry serializerRegistry, LinqProvider linqProvider)
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19 changes: 19 additions & 0 deletions tests/MongoDB.Driver.Tests/ProjectionDefinitionBuilderTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,7 @@
*/

using System.Linq;
using System.Text;
using FluentAssertions;
using MongoDB.Bson;
using MongoDB.Bson.Serialization;
Expand Down Expand Up @@ -61,6 +62,24 @@ public void Combine_with_redundant_fields_using_extension_method()
Assert(projection, "{LastName: 0, fn: 1}");
}

[Fact]
public void Combine_many_fields_should_not_overflow_stack_on_Render()
{
var subject = CreateSubject<Person>();

var projection = subject.Include(x => x.FirstName);
var expectedProjection = new StringBuilder("{fn: 1");
for (int i = 0; i < 10000; i++)
{
var field = $"Field{i}";
projection = projection.Include(field);
expectedProjection.Append($", {field}: 1");
}
expectedProjection.Append("}");

Assert(projection, expectedProjection.ToString());
}

[Fact]
public void ElemMatch()
{
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