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database.yml与每个参数调用明确，在下面的文件它使用一些字符我不明白。每行和符号（&，*，<<）是什么意思，我如何读取此文件？

 开发：& default 
 adapter：postgresql 
 database：dev_development 
 
 test：& test 
<< ;: * default 
 database：test_test 
 
 
 cucumber：
<< ;: * test 
 
 production：
<< ;: * default 
数据库：test_production 
  

解决方案

; 标记节点的别名（在您的示例中& default 将开发节点别名为default）和 * 引用名为default的别名节点。 < <：插入该节点的内容。

允许我引用YAML规格：

重复节点（对象）首先由锚点标记（用&符号&标记），然后再别名

  test：& test 
<< ;: * default 
  

$ b b

实际上扩展到

  test：& test 
 adapter：postgresql＃from default别名
数据库：dev_development＃从默认别名
  

同时使测试节点以及在别名测试下可用。
查看 YAML规范 - 2.2结构的详细信息（或者如果您还需要moar docs ++： 3.2.2.2。锚点和别名）

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

解决方案

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.

Allow me to quote the YAML spec here:

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

so parts of your example

test: &test
  <<: *default

actually expand to

test: &test
  adapter: postgresql       # from the "default" alias
  database: dev_development # from the "default" alias

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