MongoDB代码实例2，创建索引

            var database = client.GetDatabase("MyTestDB2");
            var collection = database.GetCollection<UserInfo>("UserInfo");

 
           
            var indexModel = new CreateIndexModel<UserInfo>(
               Builders<UserInfo>.IndexKeys.Ascending(_ => _.Name), new CreateIndexOptions
               {
                   Name = "UerInfo_index_name",
                   Unique = true,  //唯一值索引
               });
            var indexname = collection.Indexes.CreateOne(indexModel);

collection.Indexes.CreateOne( Builders<UserInfo>.IndexKeys.Hashed(m=>m.Id)); //设置Id为哈希类型，并建立索引，哈希类型是否以后分片集群做准备的

注意：索引的创建不受事务控制

查询现有索引：

collection.Indexes.List().ToList();

 如何判断插入重复的数据（违法唯一值索引）

            var database = client.GetDatabase("MyTestDB2");
            var collection = database.GetCollection<UserInfo>("UserInfo");
            try
            {
                collection.InsertOne(new UserInfo
                {
                    Name = "JackTan"
                });
            }
            catch (MongoWriteException ex)
            {
                if(ex.WriteError.Category == ServerErrorCategory.DuplicateKey)
                {
                    //插入重复数据
                }
                throw;
            }