CSHARP-2351: Add documentation sample for causal consistency.

Author: DmitryLukyanov

tests/MongoDB.Driver.Examples/CausalConsistencyExamples.cs

@@ -0,0 +1,129 @@
+/* Copyright 2018-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 FluentAssertions;
+using MongoDB.Bson;
+using MongoDB.Driver.Core.TestHelpers.XunitExtensions;
+using System;
+using System.Collections.Generic;
+using Xunit;
+
+namespace MongoDB.Driver.Examples
+{
+    public class CausalConsistencyExamples
+    {
+        [Fact]
+        public void Causal_Consistency_Example_1()
+        {
+            RequireServer.Check().SupportsCausalConsistency();
+
+            string testDatabaseName = "test";
+            string itemsCollectionName = "items";
+            var client = CreateClient();
+            DropCollection(client, testDatabaseName, itemsCollectionName);
+
+            // Start Causal Consistency Example 1
+            using (var session1 = client.StartSession(new ClientSessionOptions { CausalConsistency = true }))
+            {
+                var currentDate = DateTime.UtcNow.Date;
+                var items = client.GetDatabase("test", new MongoDatabaseSettings
+                    {
+                        ReadConcern = ReadConcern.Majority,
+                        WriteConcern = new WriteConcern(
+                            WriteConcern.WMode.Majority,
+                            TimeSpan.FromMilliseconds(1000))
+                    })
+                    .GetCollection<BsonDocument>("items");
+
+                items.UpdateOne(session1,
+                    Builders<BsonDocument>.Filter.And(
+                        Builders<BsonDocument>.Filter.Eq("sku", "111"),
+                        Builders<BsonDocument>.Filter.Eq("end", BsonNull.Value)),
+                    Builders<BsonDocument>.Update.Set("end", currentDate));
+
+                items.InsertOne(session1, new BsonDocument
+                {
+                    {"sku", "nuts-111"},
+                    {"name", "Pecans"},
+                    {"start", currentDate}
+                });
+            }
+            // End Causal Consistency Example 1
+
+            var result = client.GetDatabase(testDatabaseName).GetCollection<BsonDocument>(itemsCollectionName).Find("{}").FirstOrDefault();
+            RemoveIds(new[] { result });
+            result["start"].Should().NotBeNull();
+            result.Remove("start");
+            result.Should().Be("{ \"sku\" : \"nuts-111\", \"name\" : \"Pecans\" }");           
+        }
+
+        [Fact]
+        public void Causal_Consistency_Example_2()
+        {
+            RequireServer.Check().SupportsCausalConsistency();
+
+            string testDatabaseName = "test";
+            string itemsCollectionName = "items";
+            var client = CreateClient();
+            DropCollection(client, testDatabaseName, itemsCollectionName);
+
+            using (var session1 = client.StartSession(new ClientSessionOptions { CausalConsistency = true }))
+            {
+                client.GetDatabase(testDatabaseName).RunCommand<BsonDocument>(session1, "{ ping : 1 }");
+
+                // Start Causal Consistency Example 2
+                using (var session2 = client.StartSession(new ClientSessionOptions { CausalConsistency = true }))
+                {
+                    session2.AdvanceClusterTime(session1.ClusterTime);
+                    session2.AdvanceOperationTime(session1.OperationTime);
+
+                    var items = client.GetDatabase("test", new MongoDatabaseSettings
+                        {
+                            ReadPreference = ReadPreference.Secondary,
+                            ReadConcern = ReadConcern.Majority,
+                            WriteConcern = new WriteConcern(WriteConcern.WMode.Majority, TimeSpan.FromMilliseconds(1000))
+                        })
+                        .GetCollection<BsonDocument>("items");
+
+                    var filter = Builders<BsonDocument>.Filter.Eq("end", BsonNull.Value);
+                    foreach (var item in items.Find(session2, filter).ToEnumerable())
+                    {
+                        // process item
+                    }
+                }
+                // End Causal Consistency Example 2
+            }
+        }
+
+        private IMongoClient CreateClient()
+        {
+            var connectionString = CoreTestConfiguration.ConnectionString.ToString();
+            return new MongoClient(connectionString);
+        }
+
+        private void DropCollection(IMongoClient client, string databaseName, string collectionName)
+        {
+            client.GetDatabase(databaseName).DropCollection(collectionName);
+        }
+
+        private void RemoveIds(IEnumerable<BsonDocument> documents)
+        {
+            foreach (var document in documents)
+            {
+                document.Remove("_id");
+            }
+        }
+    }
+}

tests/MongoDB.Driver.Examples/MongoDB.Driver.Examples.csproj

@@ -65,6 +65,7 @@
   </ItemGroup>
   <ItemGroup>
     <Compile Include="AggregatePrimer.cs" />
+    <Compile Include="CausalConsistencyExamples.cs" />
     <Compile Include="ChangeStreamExamples.cs" />
     <Compile Include="DocumentationExamples.cs" />
     <Compile Include="IndexesPrimer.cs" />