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CSHARP-5551: Support KeyValuePair.Create<TKey,TValue>method in LINQ (#1661)
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‎src/MongoDB.Driver/Linq/Linq3Implementation/Reflection/KeyValuePairMethod.cs

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/* Copyright 2010-present MongoDB Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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using System.Collections.Generic;
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using System.Reflection;
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#if NET6_0_OR_GREATER || NETSTANDARD2_1_OR_GREATER
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namespace MongoDB.Driver.Linq.Linq3Implementation.Reflection
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{
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internal static class KeyValuePairMethod
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{
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// private static fields
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private static readonly MethodInfo __create;
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// static constructor
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static KeyValuePairMethod()
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{
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__create = ReflectionInfo.Method((object key, object value) => KeyValuePair.Create(key, value));
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}
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// public properties
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public static MethodInfo Create => __create;
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}
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}
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#endif

‎src/MongoDB.Driver/Linq/Linq3Implementation/Translators/ExpressionToAggregationExpressionTranslators/MethodTranslators/CreateMethodToAggregationExpressionTranslator.cs

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using System.Reflection;
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using MongoDB.Bson.Serialization;
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using MongoDB.Bson.Serialization.Serializers;
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using MongoDB.Driver.Linq.Linq3Implementation.Ast;
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using MongoDB.Driver.Linq.Linq3Implementation.Ast.Expressions;
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using MongoDB.Driver.Linq.Linq3Implementation.Misc;
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using MongoDB.Driver.Linq.Linq3Implementation.Reflection;
@@ -87,6 +88,14 @@ public static TranslatedExpression Translate(TranslationContext context, MethodC
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return new TranslatedExpression(expression, ast, tupleSerializer);
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}
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#if NET6_0_OR_GREATER || NETSTANDARD2_1_OR_GREATER
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if (method.Is(KeyValuePairMethod.Create))
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{
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var keyExpression = arguments[0];
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var valueExpression = arguments[1];
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return NewKeyValuePairExpressionToAggregationExpressionTranslator.Translate(context, expression, keyExpression, valueExpression);
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}
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#endif
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throw new ExpressionNotSupportedException(expression);
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}
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‎src/MongoDB.Driver/Linq/Linq3Implementation/Translators/ExpressionToAggregationExpressionTranslators/NewExpressionToAggregationExpressionTranslator.cs

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@@ -46,6 +46,10 @@ public static TranslatedExpression Translate(TranslationContext context, NewExpr
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{
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return NewTupleExpressionToAggregationExpressionTranslator.Translate(context, expression);
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}
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if (NewKeyValuePairExpressionToAggregationExpressionTranslator.CanTranslate(expression))
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{
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return NewKeyValuePairExpressionToAggregationExpressionTranslator.Translate(context, expression);
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}
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return MemberInitExpressionToAggregationExpressionTranslator.Translate(context, expression, expression, Array.Empty<MemberBinding>());
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}
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}

‎src/MongoDB.Driver/Linq/Linq3Implementation/Translators/ExpressionToAggregationExpressionTranslators/NewKeyValuePairExpressionToAggregationExpressionTranslator.cs

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/* Copyright 2010-present MongoDB Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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using System;
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using System.Collections.Generic;
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using System.Linq.Expressions;
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using MongoDB.Bson.Serialization;
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using MongoDB.Driver.Linq.Linq3Implementation.Ast.Expressions;
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namespace MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToAggregationExpressionTranslators
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{
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internal static class NewKeyValuePairExpressionToAggregationExpressionTranslator
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{
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public static bool CanTranslate(NewExpression expression)
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=> expression.Type.IsConstructedGenericType && expression.Type.GetGenericTypeDefinition() == typeof(KeyValuePair<,>);
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public static TranslatedExpression Translate(TranslationContext context, NewExpression expression)
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{
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var arguments = expression.Arguments;
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var keyExpression = arguments[0];
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var valueExpression = arguments[1];
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return Translate(context, expression, keyExpression, valueExpression);
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}
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public static TranslatedExpression Translate(
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TranslationContext context,
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Expression expression,
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Expression keyExpression,
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Expression valueExpression)
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{
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var keyTranslation = ExpressionToAggregationExpressionTranslator.Translate(context, keyExpression);
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var valueTranslation = ExpressionToAggregationExpressionTranslator.Translate(context, valueExpression);
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var ast = AstExpression.ComputedDocument([
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AstExpression.ComputedField("Key", keyTranslation.Ast),
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AstExpression.ComputedField("Value", valueTranslation.Ast)
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]);
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var serializer = CreateResultSerializer(expression.Type, keyTranslation.Serializer, valueTranslation.Serializer);
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return new TranslatedExpression(expression, ast, serializer);
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}
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private static IBsonSerializer CreateResultSerializer(Type resultType, IBsonSerializer keySerializer, IBsonSerializer valueSerializer)
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{
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var constructorInfo = resultType.GetConstructor([keySerializer.ValueType, valueSerializer.ValueType]);
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var classMap = new BsonClassMap(resultType);
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classMap.MapConstructor(constructorInfo);
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classMap.AutoMap();
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classMap.GetMemberMap("Key").SetSerializer(keySerializer);
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classMap.GetMemberMap("Value").SetSerializer(valueSerializer);
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classMap.Freeze();
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// have to use BsonClassMapSerializer here to mimic the MemberInitExpressionToAggregationExpressionTranslator to avoid risking a behavioral breaking change
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var serializerType = typeof(BsonClassMapSerializer<>).MakeGenericType(resultType);
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return (IBsonSerializer)Activator.CreateInstance(serializerType, classMap);
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}
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}
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}

‎tests/MongoDB.Driver.Tests/Linq/Linq3Implementation/Translators/ExpressionToAggregationExpressionTranslators/NewKeyValuePairExpressionToAggregationExpressionTranslatorTests.cs

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/* Copyright 2010-present MongoDB Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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using System.Collections.Generic;
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using System.Linq;
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using FluentAssertions;
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using MongoDB.Driver.TestHelpers;
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using Xunit;
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namespace MongoDB.Driver.Tests.Linq.Linq3Implementation.Translators.ExpressionToAggregationExpressionTranslators;
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#if NET6_0_OR_GREATER || NETCOREAPP3_1_OR_GREATER
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public class NewKeyValuePairExpressionToAggregationExpressionTranslatorTests : LinqIntegrationTest<NewKeyValuePairExpressionToAggregationExpressionTranslatorTests.ClassFixture>
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{
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public NewKeyValuePairExpressionToAggregationExpressionTranslatorTests(ClassFixture fixture)
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: base(fixture)
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{
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}
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[Fact]
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public void NewKeyValuePair_should_translate()
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{
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var collection = Fixture.Collection;
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var queryable = collection.AsQueryable()
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.Select(d => new KeyValuePair<string,int>("X", d.X));
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var stages = Translate(collection, queryable);
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AssertStages(stages, "{ $project : { Key : 'X', Value : '$X', _id : 0 } }");
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var result = queryable.Single();
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result.Key.Should().Be("X");
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result.Value.Should().Be(42);
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}
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[Fact]
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public void KeyValuePair_Create_should_translate()
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{
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var collection = Fixture.Collection;
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var queryable = collection.AsQueryable()
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.Select(d => KeyValuePair.Create("X", d.X));
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var stages = Translate(collection, queryable);
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AssertStages(stages, "{ $project : { Key : 'X', Value : '$X', _id : 0 } }");
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var result = queryable.Single();
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result.Key.Should().Be("X");
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result.Value.Should().Be(42);
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}
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public class C
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{
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public int X { get; set; }
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}
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public sealed class ClassFixture : MongoCollectionFixture<C>
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{
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protected override IEnumerable<C> InitialData =>
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[
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new C { X = 42 }
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];
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}
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}
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#endif

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