&,<<, * 在这个 database.yml 文件中是什么意思? [英] What do the &,<<, * mean in this database.yml file?

问题描述

到目前为止，我只使用了明确调用每个参数的 database.yml，在下面的文件中它使用了一些我不理解的字符.每行和符号(&,*,<<) 是什么意思，我如何读取这个文件?

Up until now I have only used database.yml with each parameter called out explicitly, in the file below it uses some characters I do not understand. What does each line and symbol(&,*,<<) mean, how do i read this file?

development: &default
  adapter: postgresql
  database: dev_development

test: &test
  <<: *default
  database: test_test


cucumber:
  <<: *test

production:
  <<: *default
  database: test_production

推荐答案

& 标记节点的别名(在您的示例中，&default 为开发设置别名节点作为默认")并且 * 引用名称为默认"的别名节点.<<: 插入该节点的内容.

The & marks an alias for the node (in your example &default aliases the development node as "default") and the * references the aliased node with the name "default". The <<: inserts the content of that node.

请允许我在这里引用 YAML 规范:

Allow me to quote the YAML spec here:

重复的节点(对象)首先由一个锚点标识(用 & 符号标记 - &")，然后再使用别名(用星号引用 - *").

Repeated nodes (objects) are first identified by an anchor (marked with the ampersand - "&"), and are then aliased (referenced with an asterisk - "*") thereafter.

所以你的例子的一部分

development: &default
  adapter: postgresql
  database: dev_development

test: &test
  <<: *default
  database: test_test

实际上展开为

development: &default
  adapter: postgresql
  database: dev_development

test: &test
  adapter: postgresql       # from the "default" alias
  database: test_test       # overridden by the duplicate key

同时使test"节点在别名test"下也可用.

and at the same time make the "test" node as well available under the alias "test".

查看 YAML 规范 - 2.2 结构 了解更多信息详细信息(或者如果您甚至需要 moar docs++:3.2.2.2. 锚和别名)

Have a look at the YAML specification - 2.2 Structures for further details (or if you need even moar docs++: 3.2.2.2. Anchors and Aliases)

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