CSHARP-2108: Subtracting one date from another in LINQ. (#837)

Author: rstam

src/MongoDB.Driver/Linq/Linq3Implementation/Ast/Expressions/AstDateDiffExpression.cs

@@ -76,7 +76,7 @@ public AstDateDiffExpression Update(
             AstExpression timezone,
             AstExpression startOfWeek)
         {
-            if (startDate == _startDate && EndDate == _endDate && unit == _unit && startOfWeek == _startOfWeek && timezone == _timezone)
+            if (startDate == _startDate && endDate == _endDate && unit == _unit && startOfWeek == _startOfWeek && timezone == _timezone)
             {
                 return this;
             }

tests/MongoDB.Driver.Tests/Linq/Linq3ImplementationTests/Jira/CSharp2108Tests.cs

@@ -0,0 +1,95 @@
+/* Copyright 2010-present 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.Globalization;
+using System.Linq;
+using FluentAssertions;
+using MongoDB.Driver.Core.Misc;
+using MongoDB.Driver.Core.TestHelpers.XunitExtensions;
+using MongoDB.Driver.Linq;
+using Xunit;
+
+namespace MongoDB.Driver.Tests.Linq.Linq3ImplementationTests.Jira
+{
+    public class CSharp2108Tests : Linq3IntegrationTest
+    {
+        [Fact]
+        public void Aggregate_Project_should_work()
+        {
+            RequireServer.Check().Supports(Feature.DateOperatorsNewIn50);
+            var collection = CreateCollection();
+            var endDate = DateTime.Parse("2020-01-03Z", null, DateTimeStyles.AdjustToUniversal);
+
+            var queryable = collection.Aggregate()
+                .Sort(Builders<C>.Sort.Ascending(x => x.Id))
+                .Project(x => new { Days = endDate.Subtract(x.StartDate, DateTimeUnit.Day) });
+
+            var stages = Translate(collection, queryable);
+            AssertStages(
+                stages,
+                "{ $sort : { _id : 1 } }",
+                "{ $project : { Days : { $dateDiff : { startDate : '$StartDate', endDate : ISODate('2020-01-03T00:00:00Z'), unit : 'day' } }, _id : 0 } }");
+
+            var results = queryable.ToList();
+            results.Should().HaveCount(2);
+            results[0].ShouldBeEquivalentTo(new { Days = 2 });
+            results[1].ShouldBeEquivalentTo(new { Days = 1 });
+        }
+
+        [Fact]
+        public void Queryable_Select_should_work()
+        {
+            RequireServer.Check().Supports(Feature.DateOperatorsNewIn50);
+            var collection = CreateCollection();
+            var endDate = DateTime.Parse("2020-01-03Z", null, DateTimeStyles.AdjustToUniversal);
+
+            var queryable = collection.AsQueryable()
+                .OrderBy(x => x.Id)
+                .Select(x => new { Days = endDate.Subtract(x.StartDate, DateTimeUnit.Day) });
+
+            var stages = Translate(collection, queryable);
+            AssertStages(
+                stages,
+                "{ $sort : { _id : 1 } }",
+                "{ $project : { Days : { $dateDiff : { startDate : '$StartDate', endDate : ISODate('2020-01-03T00:00:00Z'), unit : 'day' } }, _id : 0 } }");
+
+            var results = queryable.ToList();
+            results.Should().HaveCount(2);
+            results[0].ShouldBeEquivalentTo(new { Days = 2 });
+            results[1].ShouldBeEquivalentTo(new { Days = 1 });
+        }
+
+        private IMongoCollection<C> CreateCollection()
+        {
+            var collection = GetCollection<C>();
+
+            var documents = new[]
+            {
+                new C { Id = 1, StartDate = DateTime.Parse("2020-01-01Z", null, DateTimeStyles.AdjustToUniversal) },
+                new C { Id = 2, StartDate = DateTime.Parse("2020-01-02Z", null, DateTimeStyles.AdjustToUniversal) }
+            };
+            CreateCollection(collection, documents);
+
+            return collection;
+        }
+
+        private class C
+        {
+            public int Id { get; set; }
+            public DateTime StartDate { get; set; }
+        }
+    }
+}