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CSHARP-4883: Support SkipWhile and TakeWhile methods in LINQ.
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‎src/MongoDB.Driver/Linq/Linq3Implementation/Ast/Expressions/AstExpression.cs‎

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@@ -868,6 +868,16 @@ public static AstExpression Sum(AstExpression array)
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return new AstUnaryExpression(AstUnaryOperator.Sum, array);
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}
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public static AstExpression Switch(IEnumerable<AstSwitchExpressionBranch> branches, AstExpression @default = null)
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{
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return new AstSwitchExpression(branches, @default);
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}
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public static AstExpression Switch(IEnumerable<(AstExpression Case, AstExpression Then)> branches, AstExpression @default = null)
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{
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return new AstSwitchExpression(branches.Select(branch => new AstSwitchExpressionBranch(branch.Case, branch.Then)), @default);
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}
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public static AstExpression ToLower(AstExpression arg)
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{
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if (arg is AstConstantExpression constantExpression && constantExpression.Value.BsonType == BsonType.String)

‎src/MongoDB.Driver/Linq/Linq3Implementation/Reflection/EnumerableMethod.cs‎

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@@ -155,6 +155,7 @@ internal static class EnumerableMethod
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private static readonly MethodInfo __singleOrDefaultWithPredicate;
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private static readonly MethodInfo __singleWithPredicate;
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private static readonly MethodInfo __skip;
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private static readonly MethodInfo __skipWhile;
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private static readonly MethodInfo __sumDecimal;
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private static readonly MethodInfo __sumDecimalWithSelector;
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private static readonly MethodInfo __sumDouble;
@@ -176,6 +177,7 @@ internal static class EnumerableMethod
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private static readonly MethodInfo __sumSingle;
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private static readonly MethodInfo __sumSingleWithSelector;
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private static readonly MethodInfo __take;
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private static readonly MethodInfo __takeWhile;
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private static readonly MethodInfo __thenBy;
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private static readonly MethodInfo __thenByDescending;
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private static readonly MethodInfo __toArray;
@@ -320,6 +322,7 @@ static EnumerableMethod()
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__singleOrDefaultWithPredicate = ReflectionInfo.Method((IEnumerable<object> source, Func<object, bool> predicate) => source.SingleOrDefault(predicate));
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__singleWithPredicate = ReflectionInfo.Method((IEnumerable<object> source, Func<object, bool> predicate) => source.Single(predicate));
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__skip = ReflectionInfo.Method((IEnumerable<object> source, int count) => source.Skip(count));
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__skipWhile = ReflectionInfo.Method((IEnumerable<object> source, Func<object, bool> predicate) => source.SkipWhile(predicate));
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__sumDecimal = ReflectionInfo.Method((IEnumerable<decimal> source) => source.Sum());
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__sumDecimalWithSelector = ReflectionInfo.Method((IEnumerable<object> source, Func<object, decimal> selector) => source.Sum(selector));
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__sumDouble = ReflectionInfo.Method((IEnumerable<double> source) => source.Sum());
@@ -341,6 +344,7 @@ static EnumerableMethod()
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__sumSingle = ReflectionInfo.Method((IEnumerable<float> source) => source.Sum());
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__sumSingleWithSelector = ReflectionInfo.Method((IEnumerable<object> source, Func<object, float> selector) => source.Sum(selector));
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__take = ReflectionInfo.Method((IEnumerable<object> source, int count) => source.Take(count));
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__takeWhile = ReflectionInfo.Method((IEnumerable<object> source, Func<object, bool> predicate) => source.TakeWhile(predicate));
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__thenBy = ReflectionInfo.Method((IOrderedEnumerable<object> source, Func<object, object> keySelector) => source.ThenBy(keySelector));
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__thenByDescending = ReflectionInfo.Method((IOrderedEnumerable<object> source, Func<object, object> keySelector) => source.ThenByDescending(keySelector));
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__toArray = ReflectionInfo.Method((IEnumerable<object> source) => source.ToArray());
@@ -484,6 +488,7 @@ static EnumerableMethod()
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public static MethodInfo SingleOrDefaultWithPredicate => __singleOrDefaultWithPredicate;
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public static MethodInfo SingleWithPredicate => __singleWithPredicate;
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public static MethodInfo Skip => __skip;
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public static MethodInfo SkipWhile => __skipWhile;
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public static MethodInfo SumDecimal => __sumDecimal;
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public static MethodInfo SumDecimalWithSelector => __sumDecimalWithSelector;
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public static MethodInfo SumDouble => __sumDouble;
@@ -505,6 +510,7 @@ static EnumerableMethod()
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public static MethodInfo SumSingle => __sumSingle;
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public static MethodInfo SumSingleWithSelector => __sumSingleWithSelector;
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public static MethodInfo Take => __take;
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public static MethodInfo TakeWhile => __takeWhile;
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public static MethodInfo ThenBy => __thenBy;
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public static MethodInfo ThenByDescending => __thenByDescending;
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public static MethodInfo ToArray => __toArray;

‎src/MongoDB.Driver/Linq/Linq3Implementation/Reflection/QueryableMethod.cs‎

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@@ -101,6 +101,7 @@ internal static class QueryableMethod
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private static readonly MethodInfo __singleOrDefaultWithPredicate;
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private static readonly MethodInfo __singleWithPredicate;
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private static readonly MethodInfo __skip;
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private static readonly MethodInfo __skipWhile;
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private static readonly MethodInfo __sumDecimal;
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private static readonly MethodInfo __sumDecimalWithSelector;
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private static readonly MethodInfo __sumDouble;
@@ -122,6 +123,7 @@ internal static class QueryableMethod
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private static readonly MethodInfo __sumSingle;
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private static readonly MethodInfo __sumSingleWithSelector;
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private static readonly MethodInfo __take;
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private static readonly MethodInfo __takeWhile;
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private static readonly MethodInfo __thenBy;
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private static readonly MethodInfo __thenByDescending;
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private static readonly MethodInfo __union;
@@ -209,6 +211,7 @@ static QueryableMethod()
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__singleOrDefaultWithPredicate = ReflectionInfo.Method((IQueryable<object> source, Expression<Func<object, bool>> predicate) => source.SingleOrDefault(predicate));
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__singleWithPredicate = ReflectionInfo.Method((IQueryable<object> source, Expression<Func<object, bool>> predicate) => source.Single(predicate));
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__skip = ReflectionInfo.Method((IQueryable<object> source, int count) => Queryable.Skip(source, count));
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__skipWhile = ReflectionInfo.Method((IQueryable<object> source, Expression<Func<object, bool>> predicate) => Queryable.SkipWhile(source, predicate));
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__sumDecimal = ReflectionInfo.Method((IQueryable<decimal> source) => source.Sum());
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__sumDecimalWithSelector = ReflectionInfo.Method((IQueryable<object> source, Expression<Func<object, decimal>> selector) => source.Sum(selector));
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__sumDouble = ReflectionInfo.Method((IQueryable<double> source) => source.Sum());
@@ -230,6 +233,7 @@ static QueryableMethod()
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__sumSingle = ReflectionInfo.Method((IQueryable<float> source) => source.Sum());
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__sumSingleWithSelector = ReflectionInfo.Method((IQueryable<object> source, Expression<Func<object, float>> selector) => source.Sum(selector));
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__take = ReflectionInfo.Method((IQueryable<object> source, int count) => Queryable.Take(source, count));
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__takeWhile = ReflectionInfo.Method((IQueryable<object> source, Expression<Func<object, bool>> predicate) => Queryable.TakeWhile(source, predicate));
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__thenBy = ReflectionInfo.Method((IOrderedQueryable<object> source, Expression<Func<object, object>> keySelector) => source.ThenBy(keySelector));
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__thenByDescending = ReflectionInfo.Method((IOrderedQueryable<object> source, Expression<Func<object, object>> keySelector) => source.ThenByDescending(keySelector));
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__union = ReflectionInfo.Method((IQueryable<object> source1, IEnumerable<object> source2) => source1.Union(source2));
@@ -316,6 +320,7 @@ static QueryableMethod()
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public static MethodInfo SingleOrDefaultWithPredicate => __singleOrDefaultWithPredicate;
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public static MethodInfo SingleWithPredicate => __singleWithPredicate;
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public static MethodInfo Skip => __skip;
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public static MethodInfo SkipWhile => __skipWhile;
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public static MethodInfo SumDecimal => __sumDecimal;
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public static MethodInfo SumDecimalWithSelector => __sumDecimalWithSelector;
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public static MethodInfo SumDouble => __sumDouble;
@@ -337,6 +342,7 @@ static QueryableMethod()
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public static MethodInfo SumSingle => __sumSingle;
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public static MethodInfo SumSingleWithSelector => __sumSingleWithSelector;
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public static MethodInfo Take => __take;
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public static MethodInfo TakeWhile => __takeWhile;
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public static MethodInfo ThenBy => __thenBy;
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public static MethodInfo ThenByDescending => __thenByDescending;
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public static MethodInfo Union => __union;

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

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@@ -177,6 +177,10 @@ public static TranslatedExpression Translate(TranslationContext context, MethodC
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case "Take":
178178
return SkipOrTakeMethodToAggregationExpressionTranslator.Translate(context, expression);
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180+
case "SkipWhile":
181+
case "TakeWhile":
182+
return SkipWhileOrTakeWhileMethodToAggregationExpressionTranslator.Translate(context, expression);
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case "StandardDeviationPopulation":
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case "StandardDeviationSample":
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return StandardDeviationMethodsToAggregationExpressionTranslator.Translate(context, expression);

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

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@@ -0,0 +1,108 @@
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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.Linq;
17+
using System.Linq.Expressions;
18+
using System.Reflection;
19+
using MongoDB.Bson;
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using MongoDB.Driver.Linq.Linq3Implementation.Ast;
21+
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;
24+
using MongoDB.Driver.Linq.Linq3Implementation.Serializers;
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namespace MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToAggregationExpressionTranslators.MethodTranslators
27+
{
28+
internal static class SkipWhileOrTakeWhileMethodToAggregationExpressionTranslator
29+
{
30+
private static MethodInfo[] __skipWhileOrTakeWhileMethods =
31+
{
32+
EnumerableMethod.SkipWhile,
33+
EnumerableMethod.TakeWhile,
34+
QueryableMethod.SkipWhile,
35+
QueryableMethod.TakeWhile
36+
};
37+
38+
private static MethodInfo[] __skipWhileMethods =
39+
{
40+
EnumerableMethod.SkipWhile,
41+
QueryableMethod.SkipWhile
42+
};
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44+
private static MethodInfo[] __takeWhileMethods =
45+
{
46+
EnumerableMethod.TakeWhile,
47+
QueryableMethod.TakeWhile
48+
};
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50+
public static TranslatedExpression Translate(TranslationContext context, MethodCallExpression expression)
51+
{
52+
var method = expression.Method;
53+
var arguments = expression.Arguments;
54+
55+
if (method.IsOneOf(__skipWhileOrTakeWhileMethods))
56+
{
57+
var sourceExpression = arguments[0];
58+
var sourceTranslation = ExpressionToAggregationExpressionTranslator.TranslateEnumerable(context, sourceExpression);
59+
NestedAsQueryableHelper.EnsureQueryableMethodHasNestedAsQueryableSource(expression, sourceTranslation);
60+
var itemSerializer = ArraySerializerHelper.GetItemSerializer(sourceTranslation.Serializer);
61+
62+
var predicateExpression = arguments[1];
63+
var predicateLambda = ExpressionHelper.UnquoteLambdaIfQueryableMethod(method, predicateExpression);
64+
var predicateParameter = predicateLambda.Parameters.Single();
65+
var thisSymbol = context.CreateSymbol(predicateParameter, "this", itemSerializer);
66+
var predicateTranslation = ExpressionToAggregationExpressionTranslator.TranslateLambdaBody(context, predicateLambda, thisSymbol);
67+
68+
var (sourceBinding, sourceAst) = AstExpression.UseVarIfNotSimple("source", sourceTranslation.Ast);
69+
70+
var valueVar = AstExpression.Var("value");
71+
var valuePredicateField = AstExpression.GetField(valueVar, "predicate");
72+
var valueCountField = AstExpression.GetField(valueVar, "count");
73+
74+
var reduceAst = AstExpression.Reduce(
75+
input: sourceAst,
76+
initialValue: new BsonDocument { { "predicate", true }, { "count", 0 } },
77+
@in: AstExpression.Switch(
78+
branches:
79+
[
80+
(AstExpression.Not(valuePredicateField), valueVar),
81+
(predicateTranslation.Ast, AstExpression.ComputedDocument([new AstComputedField("predicate", true), new AstComputedField("count", AstExpression.Add(valueCountField, 1))]))
82+
],
83+
@default: AstExpression.ComputedDocument([new AstComputedField("predicate", false), new AstComputedField("count", valueCountField)])));
84+
85+
var whileVar = AstExpression.Var("while");
86+
var whileBinding = AstExpression.VarBinding(whileVar, reduceAst);
87+
var whileCountField = AstExpression.GetField(whileVar, "count");
88+
89+
var sliceAst = method switch
90+
{
91+
_ when method.IsOneOf(__skipWhileMethods) => AstExpression.Slice(sourceAst, whileCountField, int.MaxValue),
92+
_ when method.IsOneOf(__takeWhileMethods) => AstExpression.Slice(sourceAst, whileCountField),
93+
_ => throw new ExpressionNotSupportedException(expression)
94+
};
95+
96+
var ast = AstExpression.Let(
97+
sourceBinding,
98+
whileBinding,
99+
sliceAst);
100+
101+
var resultSerializer = NestedAsQueryableSerializer.CreateIEnumerableOrNestedAsQueryableSerializer(expression.Type, itemSerializer);
102+
return new TranslatedExpression(expression, ast, resultSerializer);
103+
}
104+
105+
throw new ExpressionNotSupportedException(expression);
106+
}
107+
}
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}

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