什么是Rails迁移等同于MySQL的“双”数据类型?

I can't seem to figure this one out by searching Google.

我似乎无法通过搜索谷歌找到这个。

I have an existing database which has some columns with the type of double, what would I write in my rails migration to create an equivalent column type? It's a relatively old database and there maybe a more suitable datatype to use completely, but I wanted to see what others thought.

我有一个现有的数据库，它有一些列类型为double，我要在rails迁移中编写什么来创建一个等效的列类型?这是一个相对古老的数据库，可能有一个更适合完全使用的数据类型，但是我想看看其他人是怎么想的。

I was going to use the type of :decimal, is this the best choice?

我要用的类型是:decimal，这是最好的选择吗?

Thoughts?

想法吗?

5 个解决方案

#1

There's no specific type for double, Rails tries to be smart about it:

对于double没有特定的类型，Rails试图聪明地做到这一点:

The numeric (integer/decimal/float) column definitions use the :limit option for the number of bytes in an integer column type, and the :scale/:precision options for floats.

数字(整数/十进制/浮点)列定义使用:limit选项表示整数列类型中的字节数，以及浮点数的:scale/:precision选项。

(precision is the number of significant digits; scale is how many of these fall after the decimal point.)

(精度是有效位数的个数;标度是这些数字中有多少落在小数点后)

#2

In my case (for test-db preparation):

在我的情况下(用于测试-db准备):

MySQL (with mysql2(0.3.11) driver):

MySQL(mysql2(0.3.11)驱动程序):

double(64,12)

Rails (in db/schema.rb):

Rails(db / schema.rb):

   t.float :limit=>64                    ==> failed
   t.float :limit=>53                    ==> occasionally succeeded
   t.decimal :precision=>64, :scale=>12  ==> fully succeeded

#3

You can get Rails to create a DOUBLE. I'm not sure how "officially" supported the following solution is, but it works for MySQL. Just set the limit to 53. e.g.:

您可以让Rails创建一个DOUBLE。我不确定如何“正式”支持以下解决方案，但它适用于MySQL。把上限设为53。例如:

t.float :published_at, :limit => 53, :null => true

t。float:published_at，:limit => 53，:null => true

I got the answer from this blog post and there is some more testing results regarding this there.

我从这篇博文中得到了答案，这里有更多的测试结果。

#4

I'm seeing a problem with this solution. If I have a declaration like this:

我发现这个解决方案有问题。如果我有这样的声明:

t.float :latitude, :limit => 30

everything looks great: the database schema shows the column is declared as a double. The problem is that schema.rb lacks any :limit value, so when the schema is cloned into the test environment, the column becomes a float rather than a double. Unit tests fail because there's not enough accuracy in the column.

一切看起来都很好:数据库模式显示列被声明为double。问题在于模式。rb缺少any:limit值，因此当将模式克隆到测试环境中时，列将变成浮点数而不是双精度数。单元测试失败是因为列中没有足够的准确性。

If you look at the docs for ActiveRecord column definitions what you find is this:

如果你查看ActiveRecord列定义的文档，你会发现:

:limit - Requests a maximum column length. This is number of characters for :string and :text columns and number of bytes for :binary and :integer columns.

:限制-请求最大列长度。这是:string和:text列的字符数，以及:binary和:integer列的字节数。

It's silent on the topic of floats. It appears from the code that it's a side effect of how :limit is supported that this solution works. It looks like either there's a bug in the generation of schema.rb or else it was never intended to be used this way.

在花车的话题上它是沉默的。从代码中可以看出，这是如何:该解决方案工作时所支持的limit的副作用。看起来模式生成中有一个错误。rb或者其他的，它从来没有打算用这种方式。

I'm afraid the answer may be that the :decimal data type (which I don't care for) is the fully-supported solution.

我担心答案可能是:decimal数据类型(我不喜欢)是完全支持的解决方案。

#5

In modern versions of Rails (I'm using 5.1)

在现代版本的Rails中(我使用5.1)

t.column  :field, "double"

#1