oracle 将数字 (22,21) 映射到 BigDecimal 时，结果中的 Hibernate 精度损失
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Hibernate loss of precision in results when mapping a number (22,21) to BigDecimal
提问by Riccardo Cossu
I have this column in my Oracle 11g mapped as NUMBER (21,20), which is mapped in Hibernate as:
我在 Oracle 11g 中将此列映射为 NUMBER (21,20)，在 Hibernate 中映射为：
@Column(name = "PESO", precision = 21, scale = 20, nullable = false)
public BigDecimal getWeight() {
return weight;
}
For a particular record for which the value of the column is 0.493 I get a BigDecimal whose value is 0.49299999999. It seems that somewhere there is a loss of precision due (maybe) to a Double or Float conversion, but I couldn't track it down with a simple unit test like this:
对于列值为 0.493 的特定记录，我得到一个 BigDecimal，其值为 0.49299999999。似乎某处由于（可能）由于 Double 或 Float 转换而导致精度损失，但我无法通过这样的简单单元测试来追踪它：
Double d = new Double("0.493");
System.out.println((d));
Any variant of that code, using Float, BigDecimal and various constructors gives the same result: "0.493"... Any hint on how should I map the column to avoid such issues? I'm using Hibernate 3.5.6, with JPA annotations and Hibernate API (that is Session and not EntityManager)
该代码的任何变体，使用 Float、BigDecimal 和各种构造函数都会给出相同的结果：“0.493”...关于我应该如何映射列以避免此类问题的任何提示？我使用的是 Hibernate 3.5.6，带有 JPA 注释和 Hibernate API（即 Session 而不是 EntityManager）
采纳答案by axtavt
It's a result of initializing BigDecimalfrom double:
这是BigDecimal从初始化的结果double：
System.out.println(String.format("%21.20f", new BigDecimal(0.493));
// Prints 0,49299999999999999378
So, when BigDecimalinitialized this way is saved in the database, it produces an inaccurate value, which is correctly loaded later.
因此，当以BigDecimal这种方式初始化保存在数据库中时，它会产生一个不准确的值，稍后会正确加载该值。
If BigDecimalis initialized by string or if the value is set directly in Java everything works fine.
如果BigDecimal由字符串初始化或者如果该值直接在 Java 中设置，则一切正常。
