CSHARP-1368: added $slice expression support.

Author: craiggwilson

Docs/reference/content/reference/driver/expressions.md

@@ -788,6 +788,21 @@ p => p.FavoriteNumbers.Count();
 { $size: '$FavoriteNumbers' }
 ```
 
+#### $slice
+
+```csharp
+p => p.FavoriteNumbers.Take(2)
+```
+```json
+{ $slice: ['$FavoriteNumbers', 2] }
+```
+```csharp
+p => p.FavoriteNumbers.Skip(3).Take(2)
+```
+```json
+{ $slice: ['$FavoriteNumbers', 3, 2] }
+```
+
 #### $sum
 
 ```csharp

src/MongoDB.Driver.Tests/Linq/Translators/AggregateProjectTranslatorTests.cs

@@ -948,6 +948,28 @@ public async Task Should_translate_subtract_3_numbers()
             result.Value.Result.Should().Be(-23);
         }
 
+        [Test]
+        [RequiresServer(MinimumVersion = "3.1.7")]
+        public async Task Should_translate_slice_with_2_arguments()
+        {
+            var result = await Project(x => new { Result = x.M.Take(2) });
+
+            result.Projection.Should().Be("{ Result: { \"$slice\": [\"$M\", 2] }, _id: 0 }");
+
+            result.Value.Result.Should().BeEquivalentTo(2, 4);
+        }
+
+        [Test]
+        [RequiresServer(MinimumVersion = "3.1.7")]
+        public async Task Should_translate_slice_with_3_arguments()
+        {
+            var result = await Project(x => new { Result = x.M.Skip(1).Take(2) });
+
+            result.Projection.Should().Be("{ Result: { \"$slice\": [\"$M\", 1, 2] }, _id: 0 }");
+
+            result.Value.Result.Should().BeEquivalentTo(4, 5);
+        }
+
         [Test]
         [RequiresServer(MinimumVersion = "3.1.7")]
         public async Task Should_translate_sum()

src/MongoDB.Driver/Linq/Processors/EmbeddedPipeline/EmbeddedPipelineBinder.cs

@@ -41,7 +41,9 @@ static EmbeddedPipelineBinder()
             infoBinder.Register(new MaxBinder(), MaxBinder.GetSupportedMethods());
             infoBinder.Register(new MinBinder(), MinBinder.GetSupportedMethods());
             infoBinder.Register(new SelectBinder(), SelectBinder.GetSupportedMethods());
+            infoBinder.Register(new SkipBinder(), SkipBinder.GetSupportedMethods());
             infoBinder.Register(new SumBinder(), SumBinder.GetSupportedMethods());
+            infoBinder.Register(new TakeBinder(), TakeBinder.GetSupportedMethods());
             infoBinder.Register(new ToArrayBinder(), ToArrayBinder.GetSupportedMethods());
             infoBinder.Register(new ToHashSetBinder(), ToHashSetBinder.GetSupportedMethods());
             infoBinder.Register(new ToListBinder(), ToListBinder.GetSupportedMethods());

src/MongoDB.Driver/Linq/Processors/EmbeddedPipeline/MethodCallBinders/SkipBinder.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.EmbeddedPipeline.MethodCallBinders
+{
+    internal sealed class SkipBinder : IMethodCallBinder<EmbeddedPipelineBindingContext>
+    {
+        public static IEnumerable<MethodInfo> GetSupportedMethods()
+        {
+            return MethodHelper.GetEnumerableAndQueryableMethodDefinitions("Skip");
+        }
+
+        public Expression Bind(PipelineExpression pipeline, EmbeddedPipelineBindingContext bindingContext, MethodCallExpression node, IEnumerable<Expression> arguments)
+        {
+            return new PipelineExpression(
+                new SkipExpression(
+                    pipeline.Source,
+                    arguments.Single()),
+                pipeline.Projector);
+        }
+    }
+}

src/MongoDB.Driver/Linq/Processors/EmbeddedPipeline/MethodCallBinders/TakeBinder.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.EmbeddedPipeline.MethodCallBinders
+{
+    internal sealed class TakeBinder : IMethodCallBinder<EmbeddedPipelineBindingContext>
+    {
+        public static IEnumerable<MethodInfo> GetSupportedMethods()
+        {
+            return MethodHelper.GetEnumerableAndQueryableMethodDefinitions("Take");
+        }
+
+        public Expression Bind(PipelineExpression pipeline, EmbeddedPipelineBindingContext bindingContext, MethodCallExpression node, IEnumerable<Expression> arguments)
+        {
+            return new PipelineExpression(
+                new TakeExpression(
+                    pipeline.Source,
+                    arguments.Single()),
+                pipeline.Projector);
+        }
+    }
+}

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

@@ -118,6 +118,10 @@ private BsonValue TranslateValue(Expression node)
                                 return TranslatePipeline((PipelineExpression)node);
                             case ExtensionExpressionType.Select:
                                 return TranslateSelect((SelectExpression)node);
+                            case ExtensionExpressionType.Skip:
+                                return TranslateSkip((SkipExpression)node);
+                            case ExtensionExpressionType.Take:
+                                return TranslateTake((TakeExpression)node);
                             case ExtensionExpressionType.Union:
                                 return TranslateUnion((UnionExpression)node);
                             case ExtensionExpressionType.Where:
@@ -426,6 +430,31 @@ private BsonValue TranslateSelect(SelectExpression node)
             });
         }
 
+        private BsonValue TranslateSkip(SkipExpression node)
+        {
+            var message = "$project or $group only supports Skip when immediately followed by a Take.";
+            throw new NotSupportedException(message);
+        }
+
+        private BsonValue TranslateTake(TakeExpression node)
+        {
+            var arguments = new BsonArray();
+            var skipNode = node.Source as SkipExpression;
+            if (skipNode != null)
+            {
+                arguments.Add(TranslateValue(skipNode.Source));
+                arguments.Add(TranslateValue(skipNode.Count));
+            }
+            else
+            {
+                arguments.Add(TranslateValue(node.Source));
+            }
+
+            arguments.Add(TranslateValue(node.Count));
+
+            return new BsonDocument("$slice", arguments);
+        }
+
         private BsonValue TranslateUnion(UnionExpression node)
         {
             return new BsonDocument("$setUnion", new BsonArray(new[]

src/MongoDB.Driver/MongoDB.Driver.csproj

@@ -148,6 +148,8 @@
     <Compile Include="Linq\Processors\EmbeddedPipeline\EmbeddedPipelineBindingContext.cs" />
     <Compile Include="Linq\Processors\EmbeddedPipeline\MethodCallBinders\AllBinder.cs" />
     <Compile Include="Linq\Processors\EmbeddedPipeline\MethodCallBinders\ConcatBinder.cs" />
+    <Compile Include="Linq\Processors\EmbeddedPipeline\MethodCallBinders\SkipBinder.cs" />
+    <Compile Include="Linq\Processors\EmbeddedPipeline\MethodCallBinders\TakeBinder.cs" />
     <Compile Include="Linq\Processors\EmbeddedPipeline\MethodCallBinders\ToHashSetBinder.cs" />
     <Compile Include="Linq\Processors\EmbeddedPipeline\MethodCallBinders\UnionBinder.cs" />
     <Compile Include="Linq\Processors\EmbeddedPipeline\MethodCallBinders\IntersectBinder.cs" />