如何让if或unless语句在erb模板中跨多行工作

Question

我正在尝试将一些逻辑写到厨师食谱中的erb模板。我有以下几点，我认为它们会起作用。目前该属性为nil，但它并没有像我想象的那样跳过整个代码块。如何让top语句使模板读取器跳过整个代码块？

    <% unless node['base']['logstash-forwarder']['nginx'].nil? %>
      <%= "{" %>
      <%= "\"paths\": [" %>
      <% node['base']['logstash-forwarder']['nginx'].each do |path| %>
        <% unless path.equal? node['base']['logstash-forwarder']['nginx'].last %>
        <%= "\"#{path}\"," %>
        <% end %>
      <% end %>
    <%= "\"#{node['base']['logstash-forwarder']['nginx'].last}\"" %>
    <%= " ]," %>
    <%= "\"fields\": { \"type\": \"nginx-access\" }" %>
    <%= "}" %>
  <% end %>

Answer 1

上面的代码在ERB中完全按照预期工作，请参见：

[122] pry(main)> e = ERB.new <<'EOI'
[122] pry(main)*  <% unless node['base']['logstash-forwarder']['nginx'].nil? %>
[122] pry(main)*       <%= "{" %>
[122] pry(main)*       <%= "\"paths\": [" %>
[122] pry(main)*       <% node['base']['logstash-forwarder']['nginx'].each do |path| %>
[122] pry(main)*         <% unless path.equal? node['base']['logstash-forwarder']['nginx'].last %>
[122] pry(main)*         <%= "\"#{path}\"," %>
[122] pry(main)*         <% end %>
[122] pry(main)*       <% end %>
[122] pry(main)*     <%= "\"#{node['base']['logstash-forwarder']['nginx'].last}\"" %>
[122] pry(main)*     <%= " ]," %>
[122] pry(main)*     <%= "\"fields\": { \"type\": \"nginx-access\" }" %>
[122] pry(main)*     <%= "}" %>
[122] pry(main)*   <% end %>
[122] pry(main)* EOI
=> #<ERB:0x007fe74bb35ff8
 @encoding=#<Encoding:UTF-8>,
 @filename=nil,
 @lineno=0,
 @safe_level=nil,
 @src=
  "#coding:UTF-8\n_erbout = ''; _erbout.concat \" \";  unless node['base']['logstash-forwarder']['nginx'].nil? ; _erbout.concat \"\\n      \"\n; _erbout.concat(( \"{\" ).to_s); _erbout.concat \"\\n      \"\n; _erbout.concat(( \"\\\"paths\\\": [\" ).to_s); _erbout.concat \"\\n      \"\n;  node['base']['logstash-forwarder']['nginx'].each do |path| ; _erbout.concat \"\\n        \"\n;  unless path.equal? node['base']['logstash-forwarder']['nginx'].last ; _erbout.concat \"\\n        \"\n; _erbout.concat(( \"\\\"\#{path}\\\",\" ).to_s); _erbout.concat \"\\n        \"\n;  end ; _erbout.concat \"\\n      \"\n;  end ; _erbout.concat \"\\n    \"\n; _erbout.concat(( \"\\\"\#{node['base']['logstash-forwarder']['nginx'].last}\\\"\" ).to_s); _erbout.concat \"\\n    \"\n; _erbout.concat(( \" ],\" ).to_s); _erbout.concat \"\\n    \"\n; _erbout.concat(( \"\\\"fields\\\": { \\\"type\\\": \\\"nginx-access\\\" }\" ).to_s); _erbout.concat \"\\n    \"\n; _erbout.concat(( \"}\" ).to_s); _erbout.concat \"\\n  \"\n;  end ; _erbout.concat \"\\n\"\n; _erbout.force_encoding(__ENCODING__)">
[123] pry(main)> node = { 'base' => { 'logstash-forwarder' => {}}}
=> {"base"=>{"logstash-forwarder"=>{}}}
[124] pry(main)> path = nil
=> nil
[125] pry(main)> e.result binding
=> " \n"
[126] pry(main)> 

所以问题是要么是Chef做了一些奇怪的事情(看起来不太可能)，要么你的node并不像你想象的那样nil?。

更新

从字里行间读取信息，特别是在调用.each和.last时，是否可能您的node['base']['logstash-forwarder']['nginx']实际上不是nil，而是[]

如果是这样，请将您的.nil?检查更改为.empty?