CSHARP-1650: added support for $split.

Author: craiggwilson

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

@@ -976,6 +976,57 @@ private bool TryTranslateStringMethodCall(MethodCallExpression node, out BsonVal
                         }
                     }
                     break;
+                case "Split":
+                    BsonValue separator = null;
+                    var separatorConstant = node.Arguments[0] as ConstantExpression;
+                    if (separatorConstant != null && separatorConstant.Type == typeof(char[]))
+                    {
+                        var chars = (char[])separatorConstant.Value;
+                        if (chars.Length == 1)
+                        {
+                            separator = new BsonString(new string(chars));
+                        }
+                    }
+                    else
+                    {
+                        separator = TranslateValue(node.Arguments[0]);
+                        var array = separator as BsonArray;
+                        if (array != null && array.Count == 1)
+                        {
+                            separator = array[0];
+                        }
+                        else if (array != null)
+                        {
+                            separator = null;
+                        }
+                    }
+
+                    if (separator != null)
+                    {
+                        if (node.Arguments.Count == 1)
+                        {
+                            result = new BsonDocument("$split", new BsonArray
+                            {
+                                field,
+                                separator
+                            });
+                            return true;
+                        }
+                        else if (node.Arguments.Count == 2 && node.Arguments[1].Type == typeof(StringSplitOptions))
+                        {
+                            var splitOptions = node.Arguments[1] as ConstantExpression;
+                            if (splitOptions != null && ((StringSplitOptions)splitOptions.Value) == StringSplitOptions.None)
+                            {
+                                result = new BsonDocument("$split", new BsonArray
+                                {
+                                    field,
+                                    separator
+                                });
+                                return true;
+                            }
+                        }
+                    }
+                    break;
                 case "Substring":
                     if (node.Arguments.Count == 2)
                     {

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

@@ -1117,6 +1117,28 @@ public void Should_translate_string_length()
             result.Value.Result.Should().Be(7);
         }
 
+        [SkippableFact]
+        public void Should_translate_split()
+        {
+            RequireServer.Where(minimumVersion: "3.3.6");
+
+            var result = Project(x => new { Result = x.A.Split('e') });
+            result.Projection.Should().Be("{ Result: { \"$split\": [\"$A\", \"e\" ] }, _id: 0 }");
+            result.Value.Result.Should().BeEquivalentTo("Aw", "som", "");
+
+            result = Project(x => new { Result = x.A.Split(new[] { 'e' }) });
+            result.Projection.Should().Be("{ Result: { \"$split\": [\"$A\", \"e\" ] }, _id: 0 }");
+            result.Value.Result.Should().BeEquivalentTo("Aw", "som", "");
+
+            result = Project(x => new { Result = x.A.Split(new[] { 'e' }, StringSplitOptions.None) });
+            result.Projection.Should().Be("{ Result: { \"$split\": [\"$A\", \"e\" ] }, _id: 0 }");
+            result.Value.Result.Should().BeEquivalentTo("Aw", "som", "");
+
+            result = Project(x => new { Result = x.A.Split(new[] { "es" }, StringSplitOptions.None) });
+            result.Projection.Should().Be("{ Result: { \"$split\": [\"$A\", \"es\" ] }, _id: 0 }");
+            result.Value.Result.Should().BeEquivalentTo("Aw", "ome");
+        }
+
         [SkippableFact]
         public void Should_translate_stdDevPop()
         {