如何使用C# ILP客户端向QuestDB提交空值？

已创建如下trades表：

CREATE TABLE 'trades' (
    symbol SYMBOL,
    side SYMBOL,
    price DOUBLE,
    revised_price DOUBLE,
    amount DOUBLE,
    timestamp TIMESTAMP
) timestamp (timestamp) PARTITION BY DAY WAL;

使用C#客户端（net-questdb-client）发送数据时，首次提交仅revised_price字段未知，需要传入空值，尝试代码如下：

using var sender =  Sender.New("http::addr=localhost:9000;");
await sender.Table("trades")
    .Symbol("symbol", "ETH-USD")
    .Symbol("side", "sell")
    .Column("price", 2615.54)
    .Column("amount", 0.00044)
    .Column("revised_price", null)
    .AtAsync(new DateTime(2021, 11, 25, 0, 46, 26));
await sender.SendAsync();

运行时触发错误：

Unhandled exception. QuestDB.Utils.IngressError: ServerFlushError : Bad request. 
Server Response (
        Code: `invalid`
        Message: `failed to parse line protocol:errors encountered on line(s):
error in line 1: table: storage path, column: state; cast error from protocol type: STRING to column type: DOUBLE`
        Line: `1`
        ErrorId: `c8712c23edc1-1` 
)

QuestDB的Ingress协议中，直接传递null会被解析为字符串类型，与DOUBLE字段类型冲突，正确处理空值的方式有两种：

方法1：省略空值字段 #

如果字段值为空，直接不调用对应的.Column()方法，QuestDB会自动将该字段设为NULL：

using var sender =  Sender.New("http::addr=localhost:9000;");
await sender.Table("trades")
    .Symbol("symbol", "ETH-USD")
    .Symbol("side", "sell")
    .Column("price", 2615.54)
    .Column("amount", 0.00044)
    .AtAsync(new DateTime(2021, 11, 25, 0, 46, 26));
await sender.SendAsync();

方法2：使用可空类型显式传递空值 #

通过Nullable<double>（即double?）类型传递空值，确保客户端生成正确的协议格式：

using var sender =  Sender.New("http::addr=localhost:9000;");
double? revisedPrice = null;
await sender.Table("trades")
    .Symbol("symbol", "ETH-USD")
    .Symbol("side", "sell")
    .Column("price", 2615.54)
    .Column("amount", 0.00044)
    .Column("revised_price", revisedPrice)
    .AtAsync(new DateTime(2021, 11, 25, 0, 46, 26));
await sender.SendAsync();

内容的提问来源于stack exchange，提问作者Nick Woolmer