mongodb在C#的连接以及curd写法

        // Empty ctor will get you a 
        // client with a default localhost and port #27017
        MongoClient m = new MongoClient();
        //----------------------------------------------------------------------
        // Using a connection-string
        MongoClient m1 = new MongoClient("mongodb://localhost:27017");
        //----------------------------------------------------------------------
        // Using MongoClientSettings
        MongoClient client = new MongoClient(
         new MongoClientSettings
         {
             Server = new MongoServerAddress("localhost", 27018),
                 // Giving 3 seconds for a MongoDB server to be up before we throw
                 ServerSelectionTimeout = TimeSpan.FromSeconds(3)
         });
        //----------------------------------------------------------------------
        // Using MongoUrl
        MongoClient client1 = new MongoClient(
         MongoUrl.Create("mongodb://localhost:27017"));
    }

MongoClient mongoClient = new MongoClient(configuration["DataBaseConnection:0:host"]);
                var dbAdmin = mongoClient.GetDatabase("shoppingMall");
                var buyerCollection = dbAdmin.GetCollection<Buyer>("shoppingMall.buyer");
                //新增
                ////var a= buyerCollection.InsertOneAsync(new Buyer { buyerName="管理员", buyerAge=23, buyerAddress="江汉市天府大道067号", buyerSex=‘0‘, buyerIdCard="12355544884474", buyerHeadPortrait="~/images/admin.jpg", buyerAccountNumber="admin1" });
                //查询
                //linq写法
                //var sql = from bb in buyerCollection.AsQueryable()
                //          select bb;
                //sql= sql.Where(t => t.buyerAge >= 22);
                //var retlist = sql.ToList();
                //ef写法
                //var ret = buyerCollection.AsQueryable().GroupBy(t=>new { t.buyerAge }).Where(t=>t.Key.buyerAge>=22);
                //var b = ret.ToList();

                var filterBuilder = Builders<Buyer>.Filter;
                var filter = filterBuilder.Gt("buyerAge", 10) & filterBuilder.Lt("counter", 30) & filterBuilder.Lt("counter", 30);//多个条件

                //var filter = Builders<Buyer>.Filter.Gt("buyerAge", 1);//一个条件 
                var document = await buyerCollection.FindAsync(filter);
                var res = document.ToList();

                //更新
                var updateFilter = filterBuilder.Gt("buyerAge", 20) & filterBuilder.Lt("buyerAge", 30);//多个条件

                var updated = Builders<Buyer>.Update.Set("buyerName", "李四");
                var result = buyerCollection.UpdateManyAsync(updateFilter, updated).Result;


                //删除
                var delFilter = filterBuilder.Gt("buyerAge", 20) & filterBuilder.Lt("buyerAge", 30);//多个条件

                var resut = buyerCollection.DeleteManyAsync(delFilter).Result;

"DataBaseConnection": [
    {
      "host": "mongodb://localhost:27017"
    }
  ]

        public IConfigurationRoot configuration;
        public BaseController()
        {
            //读取appsettings配置
            var builder = new ConfigurationBuilder()
        .SetBasePath(Directory.GetCurrentDirectory())
        .AddJsonFile("appsettings.json");
            configuration = builder.Build();
        }