c# mongodb 驱动程序如何将 mongo double 值转换为 c# 十进制值 [英] c# mongodb driver how to cast a mongo double value to a c# decimal one

问题描述

我有这个 bson 文档，我从 mongodb 中读取，使用 c# mongodb 驱动程序 v2.4.4.我只需要在 c# 代码中将其中的某些字段转换为十进制.我知道那里有一个双精度值，因此我尝试使用以下方法转换为十进制值:

I have this bson document which I read from mongodb, using c# mongodb driver v2.4.4. I just need to convert some field in it to decimal in a c# code. I know there is a double value there, therefore I try to convert to a decimal value using:

monto = Convert.ToDecimal(document["monto"].AsDouble)

但是，由于值是 39330000，我想驱动程序假定它是 Int32 并抛出此异常:

But, as the value is 39330000, I suppose the driver assumes it is a Int32 and throws this exception:

无法将MongoDB.Bson.BsonInt32"类型的对象转换为类型'MongoDB.Bson.BsonDouble'.

Unable to cast object of type 'MongoDB.Bson.BsonInt32' to type 'MongoDB.Bson.BsonDouble'.

也许是因为它里面没有点 (.).

Maybe because it doesn't come with the dot (.) in it.

所以，我用它来转换为十进制:

So, I'm using this to convert to decimal:

monto = Convert.ToDecimal(document["monto"].ToString())

它之所以有效是因为 c# 可以将任何包含数字的字符串转换为十进制.

And it works because c# can convert to decimal any string that contains a number.

我的问题是:有没有更好的方法将 bson double 转换为 c#decimal，而不先将其转换为字符串?

My question is: is there a better way to convert a bson double to c# decimal, without converting it to a string first ?

谢谢，再见……

推荐答案

最好的选择可能是:

monto = document["monto"].ToDecimal();

之所以如此有效，是因为抽象的 BsonValue 类型实现了如下所示的方法:

The reason why this works so nicely is that the abstract BsonValue type implements a method that looks like this:

public virtual decimal ToDecimal()

BsonValue 的具体实现(例如 BsonInt32、BsonInt64、BsonDouble 等)用无论驱动程序是否从存储的文档中反序列化 int、long 或 double，以下方法都能准确地为您提供所需的内容:

The concrete implementations of BsonValue (e.g. BsonInt32, BsonInt64, BsonDouble etc.) override this member with the below method which gives you precisely what you want, no matter if the driver deserializes an int, a long or a double from a stored document:

public override decimal ToDecimal()
{
    return (decimal)_value;
}

或者，在您的特定情况下(如果范围内的所有文档都在其monto"字段中存储了一个 int)，您可以简单地编写:

Alternatively, in your specific case (and if all documents in scope have an int stored in their "monto" field) you can simply write:

monto = Convert.ToDecimal(document["monto"].AsInt32)

甚至只是

monto = (decimal)(document["monto"].AsInt32)

语义相同.

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