blocks|key|790831|text|如果要为财务目的精确表示，则双倍或浮点值不适合，因为小数部分容易出现舍入误差。某些十进制值不能用基于二进制的浮点数表示，必须进行近似。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|790832|有关技术含量较低的介绍，请参见四舍五入浮点数的问题；如果您希望退出，请阅读关于浮点算法，每个计算机科学家应该知道什么？。|offset|length|790833|建议使用整数类型(以美分存储值)，以避免潜在的舍入错误。这种方法在使用刻度因子的MongoDB文档中被描述为“模拟货币数据”，是MongoDB+3.2和更早版本的通用解决方案。|790834|MongoDB+3.4包括一个新的十进制BSON型，它为操纵货币数据字段提供了精确的精度。|790835|entityMap|0|LINK|mutability|MUTABLE|url|http://www.theregister.co.uk/2006/08/12/floating_point_approximation/|1|http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html|2|https://docs.mongodb.com/manual/tutorial/model-monetary-data/#using-a-scale-factor|3|https://docs.mongodb.com/manual/tutorial/model-monetary-data/|4|https://docs.mongodb.com/manual/tutorial/model-monetary-data/#numeric-decimal^0|0|F|A|0|11|M|1|0|X|6|2|1J|6|3|0|H|8|4|0^^$0|@$1|2|3|4|5|6|7|Z|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|10|8|@]|9|@$D|11|E|12|1|13]|$D|14|E|15|1|16]]|A|$]]|$1|F|3|G|5|6|7|17|8|@]|9|@$D|18|E|19|1|1A]|$D|1B|E|1C|1|1D]]|A|$]]|$1|H|3|I|5|6|7|1E|8|@]|9|@$D|1F|E|1G|1|1H]]|A|$]]|$1|J|3|-4|5|6|7|1I|8|@]|9|@]|A|$]]]|K|$L|$5|M|N|O|A|$P|Q]]|R|$5|M|N|O|A|$P|S]]|T|$5|M|N|O|A|$P|U]]|V|$5|M|N|O|A|$P|W]]|X|$5|M|N|O|A|$P|Y]]]]

If you want an exact representation for financial purposes, then doubles or floating point values are unsuitable as the fractional parts are subject to rounding error. Certain decimal values cannot not be represented using binary-based floating points and must be approximated.

For a less technical intro, see <a href="http://www.theregister.co.uk/2006/08/12/floating_point_approximation/" rel="noreferrer">The trouble with rounding floating point numbers</a>; if you want to geek out, then read <a href="http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html" rel="noreferrer">What Every Computer Scientist Should Know About Floating-Point Arithmetic</a>.

The recommendation of using an integer type (storing the value in cents) is to avoid potential rounding errors. This approach is described as "<a href="https://docs.mongodb.com/manual/tutorial/model-monetary-data/#using-a-scale-factor" rel="noreferrer">Using a Scale Factor</a>" in the MongoDB documentation for <a href="https://docs.mongodb.com/manual/tutorial/model-monetary-data/" rel="noreferrer">modelling monetary data</a> and is a general workaround for MongoDB 3.2 and earlier.

MongoDB 3.4 includes a new <a href="https://docs.mongodb.com/manual/tutorial/model-monetary-data/#numeric-decimal" rel="noreferrer">Decimal BSON type</a> which provides exact precision for manipulating monetary data fields.

blocks|key|790840|text|如果不想将货币存储为美分值，则可以将1.34美元的货币存储为如下所示的对象：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|790841|{
++++major:+1,
++++minor:+34,
++++currency:+"USD"
}|code-block|syntax|javascript|790842|对这样的对象做任何数学运算都不容易，也不会使用商业舍入规则。但是无论如何，您不应该在数据库上执行任何业务逻辑，特别是当数据库是像MongoDB这样的“哑”数据库时更是如此。|790843|您应该做的是将这些对象序列化/反序列化到应用程序中的一个Money类，该类实现基本货币数学操作，尊重舍入规则，并在尝试使用不同货币单位执行操作时抛出异常($12.34+%2B+14.95€+=+error+--必须首先通过提供汇率将一种货币转换为另一种货币)。|offset|length|style|CODE|790844|entityMap^0|0|0|0|S|5|25|N|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|T|8|@$K|U|L|V|M|N]|$K|W|L|X|M|N]]|9|@]|A|$]]|$1|O|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|P|$]]

When you don't want to store currency as cent-values, you could store a currency of $1.34 as an object like this:

<pre><code>{
 major: 1,
 minor: 34,
 currency: "USD"
}
</code></pre>

Doing any math with objects like this would not be easy and would not use commercial rounding rules. But you shouldn't do any business logic on the database anyway, especially not when it's a "dumb" database like MongoDB.

What you should be doing is serialize/deserialize these objects from/to a <code>Money</code> class in your application which implements the basic currency math operations respecting the rounding rules and throws an exception when you try to do an operation with different currency units (<code>$12.34 + 14.95€ = error</code> - must convert one currency to the other currency first by providing an exchange rate).

blocks|key|1599776|text|如果您使用的是Mongoose，那么您可以在模式定义中使用getter/setter函数。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1599777|function+getDecimalNumber(val)+{++++return+(val/1000000);+}
function+setDecimalNumber(val)+{++++return+(val*1000000);+}|code-block|syntax|javascript|1599778|适用于架构对象，如|1599779|balance:+{+type:+Number,+default:+0,+get:+getDecimalNumber,+set:+setDecimalNumber+},|1599780|要乘/除的零点数取决于所需的精度。|1599781|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

If you're using Mongoose then you can use getter/setter functions in the schema definition e.g.

<pre><code>function getDecimalNumber(val) { return (val/1000000); }
function setDecimalNumber(val) { return (val*1000000); }
</code></pre>

Applicable to a schema object such as

<pre><code>balance: { type: Number, default: 0, get: getDecimalNumber, set: setDecimalNumber },
</code></pre>

The number of zeroes to multiply/divide by depends on the accuracy you want.

blocks|key|1599833|text|我知道这个帖子很旧，但在谷歌排名很高，所以.|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1599834|存储金融数据的最佳解决方案是使用精确的精度，正如MongoDB自己在这里所记录的那样，http://docs.mongodb.org/v2.6/tutorial/model-monetary-data/#monetary-value-exact-precision。|offset|length|1599835|{price:+9990,+currency:+"USD"+}|code-block|syntax|javascript|1599836|当你需要数据除以100，假设你想要2位的精度。缺点是，您总是需要以同样的精度工作。|1599837|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.mongodb.org/v2.6/tutorial/model-monetary-data/#monetary-value-exact-precision^0|0|17|2H|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|V|8|@]|9|@$D|W|E|X|1|Y]]|A|$]]|$1|F|3|G|5|H|7|Z|8|@]|9|@]|A|$I|J]]|$1|K|3|L|5|6|7|10|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|11|8|@]|9|@]|A|$]]]|N|$O|$5|P|Q|R|A|$S|T]]]]

I know this post is old but it ranks high on Google so...

The best solution for storing financial data is using exact precision as documented by MongoDB themselves here <a href="http://docs.mongodb.org/v2.6/tutorial/model-monetary-data/#monetary-value-exact-precision" rel="nofollow">http://docs.mongodb.org/v2.6/tutorial/model-monetary-data/#monetary-value-exact-precision</a>.

<pre><code>{price: 9990, currency: "USD" }
</code></pre>

And when you need the data just divide by 100 assuming you want 2 digit precision. The downside is that you always need to work with the same precision.

blocks|key|1599868|text|看起来MongoDB终于增加了对小数的支持，尽管在编写本文的时候，这只是刚刚完成的开发，但是希望它很快就可以在稳定的版本(3.4?)中使用。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1599869|https://jira.mongodb.org/browse/SERVER-1393|offset|length|1599870|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|17|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@$D|O|E|P|1|Q]]|A|$]]|$1|F|3|-4|5|6|7|R|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|C]]]]

Looks like MongoDB has finally added support for decimals, although at the time of writing this is just finished development, but hopefully it should be available very soon in stable version (3.4?). 

<a href="https://jira.mongodb.org/browse/SERVER-1393" rel="nofollow">https://jira.mongodb.org/browse/SERVER-1393</a>

blocks|key|1599897|text|MongoDb增加了对3.4版本的十进制数据类型的支持。它也可以从壳获得。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1599898|3.4用新的十进制数据类型添加对decimal128格式的支持。decimal128格式支持多达34位十进制数字(即有效数字)和指数范围为−6143至%2B6144的数字。
与双数据类型(只存储十进制值的近似值)不同，十进制数据类型存储精确值。例如，十进制NumberDecimal("+9.99+")的精确值为9.99，其中双9.99的近似值为9.9900000000000002131628.|blockquote|1599899|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.mongodb.com/master/release-notes/3.4/#decimal-type|1|https://docs.mongodb.com/master/core/shell-types/#shell-type-decimal^0|B|D|0|X|1|1|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]|$A|U|B|V|1|W]]|C|$]]|$1|D|3|E|5|F|7|X|8|@]|9|@]|C|$]]|$1|G|3|-4|5|6|7|Y|8|@]|9|@]|C|$]]]|H|$I|$5|J|K|L|C|$M|N]]|O|$5|J|K|L|C|$M|P]]]]

MongoDb added support for <a href="https://docs.mongodb.com/master/release-notes/3.4/#decimal-type" rel="noreferrer">Decimal data type in 3.4 version</a>. It is also available from the <a href="https://docs.mongodb.com/master/core/shell-types/#shell-type-decimal" rel="noreferrer">shell</a>.

<blockquote>
 3.4 adds support for the decimal128 format with the new decimal data type. The decimal128 format supports numbers with up to 34 decimal
 digits (i.e. significant digits) and an exponent range of −6143 to
 +6144.
 
 Unlike the double data type, which only stores an approximation of the
 decimal values, the decimal data type stores the exact value. For
 example, a decimal NumberDecimal("9.99") has a precise value of 9.99
 where as a double 9.99 would have an approximate value of
 9.9900000000000002131628...
</blockquote>

blocks|key|1599910|text|NodeJS用户：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1599911|注意，如果使用NodeJS，则不直接使用NumberDecimal(string)，而是使用Decimal128.fromString(string)。|1599912|参考文献：|1599913|https://www.mongodb.com/community/forums/t/how-do-i-use-numberdecimal-within-node-js/3224|unordered-list-item|offset|length|1599914|https://mongodb.github.io/node-mongodb-native/3.6/api/Decimal128.html|1599915|示例：|1599916|const+Decimal128+=+require('mongodb').Decimal128

usersCollection.findOneAndUpdate({_id:+ObjectID(this.data.userId),+"myWells.wellId":+ObjectID(this.data.wellId)},
++{+
++++$set:+{+"myWells.$.interest":+Decimal128.fromString(this.data.interest)+}
++}
)|code-block|syntax|javascript|1599917|entityMap|0|LINK|mutability|MUTABLE|url|1^0|0|0|0|0|2H|0|0|0|1X|1|0|0|0^^$0|@$1|2|3|4|5|6|7|11|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|12|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|13|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|14|8|@]|9|@$I|15|J|16|1|17]]|A|$]]|$1|K|3|L|5|H|7|18|8|@]|9|@$I|19|J|1A|1|1B]]|A|$]]|$1|M|3|N|5|6|7|1C|8|@]|9|@]|A|$]]|$1|O|3|P|5|Q|7|1D|8|@]|9|@]|A|$R|S]]|$1|T|3|-4|5|6|7|1E|8|@]|9|@]|A|$]]]|U|$V|$5|W|X|Y|A|$Z|G]]|10|$5|W|X|Y|A|$Z|L]]]]

<h2>NodeJS Users:</h2>
Note that if using NodeJS, you don't use NumberDecimal(string) directly, you instead use Decimal128.fromString(string).
References:
<ul>
<li><a href="https://www.mongodb.com/community/forums/t/how-do-i-use-numberdecimal-within-node-js/3224" rel="nofollow noreferrer">https://www.mongodb.com/community/forums/t/how-do-i-use-numberdecimal-within-node-js/3224</a></li>
<li><a href="https://mongodb.github.io/node-mongodb-native/3.6/api/Decimal128.html" rel="nofollow noreferrer">https://mongodb.github.io/node-mongodb-native/3.6/api/Decimal128.html</a></li>
</ul>
Example:
<pre><code>const Decimal128 = require('mongodb').Decimal128

usersCollection.findOneAndUpdate({_id: ObjectID(this.data.userId), &quot;myWells.wellId&quot;: ObjectID(this.data.wellId)},
 { 
 $set: { &quot;myWells.$.interest&quot;: Decimal128.fromString(this.data.interest) }
 }
)
</code></pre>

I am currently learning and applying MongoDB for a small financial related project.
<hr />
When I read <a href="http://www.manning.com/banker/" rel="nofollow noreferrer">MongoDB in Action</a>, it says:
<blockquote>
The only other issue that commonly arises with BSON numeric types is
the lack of decimal support. This means that if you’re planning on
storing currency values in MongoDB, you need to use an integer type
and keep the values in cents.
</blockquote>
<hr />
My financial related product will involve some currency values, but I am little bit confused or worried about the above statement. Here are my questions:
<ol>
<li>Can I use <code>double</code> for those <code>currency values</code> in my project?</li>
<li>What will happen or is the consequences if I directly use <code>double</code> for them?</li>
<li>If decimal type is an must-have thing for financial product, is that a bad idea to use MongoDB?</li>
<li>What does it mean <code>you need to use an integer type and keep the values in cents</code>? Does it mean that if I am going to store <code>1.34 dollars</code>, then I should store <code>134 cents</code>?</li>
</ol>

MongoDB - What about Decimal type of value?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我目前正在为一个小型金融相关项目学习和应用MongoDB。当我读到时，它说：BSON数字类型通常出现的唯一其他问题是缺乏十进制支持。这意味着，如果您计划在MongoDB中存储货币值，则需要使用整数类型，并将值保持为美分。我的金融相关产品将涉及一些货币价值，但我有点困惑或担心上述声明。以下是我的问题：我可以将double...

问MongoDB --十进制值类型如何？
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