了解Rails迁移语句(:null => false) [英] Understanding rails migration statement (:null => false)

问题描述

我试图理解以下声明，它是从Rails迁移文件中获得的:

I am trying to understand the following statement, it is from a rails migration file:

x.datetime "new",     :null => false
x.datetime "update",  :null => false

我理解这两个语句的第一部分(逗号之前的所有内容)，但不确定空白部分

I understand the the first part of both statements (everything before the comma) but I am unsure on the null portion

:null => false

这基本上是在说如果不存在，那就是假的"?逻辑似乎有点奇怪，对此进行任何澄清将大有帮助.

Is this basically saying "if it does not exist, then it is false?" The logic just seems a bit strange, any clarification on this would be greatly helpful.

推荐答案

因为它最初提到了CoffeeScript ，所以我认为问题与语法和翻译有关.为此，请参考 Peter Bloom的答案.

I had taken the question to be about syntax and translation since it originally mentioned CoffeeScript. For purpose, refer to Peter Bloom's answer.

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我不确定:null => false的确切含义.

=>运算符是Ruby中的键/值分隔符，定义了 Hash ，且:null键设置为false.在CoffeeScript/JavaScript中，Object文字与:相似-{ null: false }.

The => operator is a key/value separator in Ruby, defining a Hash with a :null key set to false. It's similar to : for an Object literal in CoffeeScript/JavaScript -- { null: false }.

在参数列表中使用时，它是允许/模仿Ruby中命名参数的一种选择.

When used in an argument list, it's one option for allowing/imitating named arguments in Ruby.

另一个主要区别是CoffeeScript/JavaScript使用String作为键，而Ruby通常使用(cs/js)与:null(rb).

The other main difference is that CoffeeScript/JavaScript use Strings for keys while Ruby typically uses Symbols -- "null" (cs/js) vs. :null (rb).

因此，CoffeeScript中的语法等效项是:

So, the syntactic equivalent in CoffeeScript would be:

x.datetime "new",     null: false
x.datetime "update",  null: false

在JavaScript中，这是:

In JavaScript, that's:

x.datetime("new",    { null: false });
x.datetime("update", { null: false });

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