CSHARP-1366: added $sample stage operator.

Author: craiggwilson

src/MongoDB.Driver.Tests/Linq/MongoQueryableTests.cs

@@ -564,6 +564,16 @@ public void OrderBy_ThenBy_ThenByDescending_with_redundant_fields_in_different_d
             act.ShouldThrow<NotSupportedException>();
         }
 
+        [Test]
+        public void Sample()
+        {
+            var query = CreateQuery().Sample(100);
+
+            Assert(query,
+                2,
+                "{ $sample: { size: 100 } }");
+        }
+
         [Test]
         public void Select_identity()
         {

src/MongoDB.Driver/Linq/Expressions/ExtensionExpressionType.cs

@@ -27,6 +27,7 @@ internal enum ExtensionExpressionType
         GroupByWithResultSelector,
         Intersect,
         OrderBy,
+        Sample,
         Select,
         SelectMany,
         Skip,

src/MongoDB.Driver/Linq/Expressions/ExtensionExpressionVisitor.cs

@@ -132,6 +132,13 @@ protected internal virtual ResultOperator VisitResultOperator(ResultOperator res
             return resultOperator.Update(this);
         }
 
+        protected internal virtual Expression VisitSample(SampleExpression node)
+        {
+            return node.Update(
+                Visit(node.Source),
+                Visit(node.Count));
+        }
+
         protected internal virtual Expression VisitSelect(SelectExpression node)
         {
             return node.Update(

src/MongoDB.Driver/Linq/Expressions/SampleExpression.cs

@@ -0,0 +1,74 @@
+/* Copyright 2015 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.
+*/
+
+using System;
+using System.Linq.Expressions;
+using MongoDB.Driver.Core.Misc;
+
+namespace MongoDB.Driver.Linq.Expressions
+{
+    internal sealed class SampleExpression : ExtensionExpression, ISourcedExpression
+    {
+        private readonly Expression _count;
+        private readonly Expression _source;
+
+        public SampleExpression(Expression source, Expression count)
+        {
+            _source = Ensure.IsNotNull(source, nameof(source));
+            _count = Ensure.IsNotNull(count, nameof(count));
+        }
+
+        public override ExtensionExpressionType ExtensionType
+        {
+            get { return ExtensionExpressionType.Sample; }
+        }
+
+        public Expression Count
+        {
+            get { return _count; }
+        }
+
+        public Expression Source
+        {
+            get { return _source; }
+        }
+
+        public override Type Type
+        {
+            get { return _source.Type; }
+        }
+
+        public override string ToString()
+        {
+            return string.Format("{0}.Sample({1})", _source.ToString(), _count.ToString());
+        }
+
+        public SampleExpression Update(Expression source, Expression count)
+        {
+            if (source != _source ||
+                count != _count)
+            {
+                return new SampleExpression(source, count);
+            }
+
+            return this;
+        }
+
+        protected internal override Expression Accept(ExtensionExpressionVisitor visitor)
+        {
+            return visitor.VisitSample(this);
+        }
+    }
+}

src/MongoDB.Driver/Linq/MongoQueryable.cs

@@ -748,6 +748,25 @@ public static IOrderedMongoQueryable<TSource> OrderByDescending<TSource, TKey>(t
             return (IOrderedMongoQueryable<TSource>)Queryable.OrderByDescending(source, keySelector);
         }
 
+        /// <summary>
+        /// Returns a sample of the elements in the <paramref name="source"/>.
+        /// </summary>
+        /// <typeparam name="TSource">The type of the elements of <paramref name="source" />.</typeparam>
+        /// <param name="source">An <see cref="IMongoQueryable{TSource}" /> to return a sample of.</param>
+        /// <param name="count">The number of elements in the sample.</param>
+        /// <returns>
+        /// A sample of the elements in the <paramref name="source"/>.
+        /// </returns>
+        public static IMongoQueryable<TSource> Sample<TSource>(this IQueryable<TSource> source, long count)
+        {
+            return (IMongoQueryable<TSource>)source.Provider.CreateQuery<TSource>(
+                Expression.Call(
+                    null,
+                    GetMethodInfo(Sample, source, count),
+                    source.Expression,
+                    Expression.Constant(count)));
+        }
+
         /// <summary>
         /// Projects each element of a sequence into a new form by incorporating the
         /// element's index.

src/MongoDB.Driver/Linq/Processors/Pipeline/MethodCallBinders/SampleBinder.cs

@@ -0,0 +1,40 @@
+/* Copyright 2015 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.
+*/
+
+using System.Collections.Generic;
+using System.Linq;
+using System.Linq.Expressions;
+using System.Reflection;
+using MongoDB.Driver.Linq.Expressions;
+
+namespace MongoDB.Driver.Linq.Processors.Pipeline.MethodCallBinders
+{
+    internal sealed class SampleBinder : IMethodCallBinder<PipelineBindingContext>
+    {
+        public static IEnumerable<MethodInfo> GetSupportedMethods()
+        {
+            return MethodHelper.GetEnumerableAndQueryableMethodDefinitions(nameof(MongoQueryable.Sample));
+        }
+
+        public Expression Bind(PipelineExpression pipeline, PipelineBindingContext bindingContext, MethodCallExpression node, IEnumerable<Expression> arguments)
+        {
+            return new PipelineExpression(
+                new SampleExpression(
+                    pipeline.Source,
+                    arguments.Single()),
+                pipeline.Projector);
+        }
+    }
+}

src/MongoDB.Driver/Linq/Processors/Pipeline/PipelineBinder.cs

@@ -39,6 +39,7 @@ static PipelineBinder()
             __methodCallBinder.Register(new MinBinder(), MinBinder.GetSupportedMethods());
             __methodCallBinder.Register(new OfTypeBinder(), OfTypeBinder.GetSupportedMethods());
             __methodCallBinder.Register(new OrderByBinder(), OrderByBinder.GetSupportedMethods());
+            __methodCallBinder.Register(new SampleBinder(), SampleBinder.GetSupportedMethods());
             __methodCallBinder.Register(new SelectBinder(), SelectBinder.GetSupportedMethods());
             __methodCallBinder.Register(new SelectManyBinder(), SelectManyBinder.GetSupportedMethods());
             __methodCallBinder.Register(new SingleBinder(), SingleBinder.GetSupportedMethods());

src/MongoDB.Driver/Linq/Translators/QueryableTranslator.cs

@@ -76,6 +76,9 @@ private void Translate(Expression node)
                     case ExtensionExpressionType.Pipeline:
                         TranslatePipeline((PipelineExpression)node);
                         return;
+                    case ExtensionExpressionType.Sample:
+                        TranslateSample((SampleExpression)node);
+                        return;
                     case ExtensionExpressionType.Select:
                         TranslateSelect((SelectExpression)node);
                         return;
@@ -192,6 +195,13 @@ private void TranslatePipeline(PipelineExpression node)
             _resultTransformer = node.ResultOperator as IResultTransformer;
         }
 
+        private void TranslateSample(SampleExpression node)
+        {
+            Translate(node.Source);
+
+            _stages.Add(new BsonDocument("$sample", new BsonDocument("size", (long)((ConstantExpression)node.Count).Value)));
+        }
+
         private void TranslateSelect(SelectExpression node)
         {
             Translate(node.Source);

src/MongoDB.Driver/MongoDB.Driver.csproj

@@ -114,6 +114,7 @@
     <Compile Include="Linq\Expressions\OrderByClause.cs" />
     <Compile Include="Linq\Expressions\ExceptExpression.cs" />
     <Compile Include="Linq\Expressions\IntersectExpression.cs" />
+    <Compile Include="Linq\Expressions\SampleExpression.cs" />
     <Compile Include="Linq\Expressions\UnionExpression.cs" />
     <Compile Include="Linq\Expressions\WhereExpression.cs" />
     <Compile Include="Linq\Expressions\ISerializationExpression.cs" />
@@ -177,6 +178,7 @@
     <Compile Include="Linq\Processors\Pipeline\MethodCallBinders\GroupByWithResultSelectorBinder.cs" />
     <Compile Include="Linq\Processors\Pipeline\MethodCallBinders\StandardDeviationSampleBinder.cs" />
     <Compile Include="Linq\Processors\Pipeline\MethodCallBinders\StandardDeviationPopulationBinder.cs" />
+    <Compile Include="Linq\Processors\Pipeline\MethodCallBinders\SampleBinder.cs" />
     <Compile Include="Linq\Processors\Pipeline\MethodCallBinders\ThenByBinder.cs" />
     <Compile Include="Linq\Processors\Pipeline\MethodCallBinders\OrderByBinder.cs" />
     <Compile Include="Linq\Processors\Pipeline\MethodCallBinders\SelectManyBinder.cs" />