Ruby-on-rails rails - collection_select 选定的值（如果已定义）？
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rails - collection_select selected value if defined?
提问by AnApprentice
I have the following:
我有以下几点：
<%= f.collection_select :role_id, roles, :id, :name, :prompt => true, :selected => 2 %>
Problem is I only want the selected value of 2 if the value @permission.role_id is nil.
问题是，如果值@permission.role_id 为零，我只想要选定的值 2。
so I tried:
所以我试过：
<%= f.collection_select :role_id, roles, :id, :name, :prompt => true, {:selected => 2 if @permission.role_id.nil?} %>
but that made Rails angry. How can I make a condition selected value based on if a separate variable is nil or not?
但这让 Rails 很生气。如何根据单独的变量是否为 nil 来创建条件选择值？
Thanks
谢谢
回答by ecoologic
ok I guess I'll feel stupid in 2 mins, but what about
好吧，我想我会在 2 分钟内感到愚蠢，但是呢
<%= f.collection_select :role_id, roles, :id, :name, prompt: true, @permission.role_id ? {} : {selected: 2 } %>
The reason why your solution is not working is that your ifcan return nil, therefor looking something like that:
您的解决方案不起作用的原因是您if可以 return nil，因此看起来像这样：
<%= f.collection_select :role_id, roles, :id, :name, :prompt => true, {nil} %>
Where {nil}is syntax error
{nil}语法错误在哪里
回答by saneshark
While the accepted solution with the ternary operator works, I don't think it is quite as readable as the following solution:
虽然使用三元运算符的公认解决方案有效，但我认为它不如以下解决方案具有可读性：
<%= f.collection_select :role_id, roles, :id, :name, :prompt => true, :selected => @permission.role_id || 2 %>
回答by Andrei S
put this in your helper
把这个放在你的助手里
def selected(permission)
if permission.role_id.nil?
return 2
else
.....
end
end
and this in your view
这在你看来
<%= f.collection_select :role_id, roles, :id, :name, :prompt => true, :selected => selected(@permission) %>
回答by Ryan
I found @ecoologic's answer didn't work for me as ruby attempted to interpret the hash as a key for a last argument instead of looking inside the hash for values.
我发现@ecoologic 的答案对我不起作用，因为 ruby 试图将哈希解释为最后一个参数的键，而不是在哈希内部查找值。
The solution was to use a 'splat'. However splats don't seem to work in that inline format, so I used the following:
解决方案是使用“ splat”。然而，splats 似乎不能以这种内联格式工作，所以我使用了以下内容：
<% selected = @permission.role_id ? {} : {selected: 2 } %>
<%= f.collection_select :role_id, roles, :id, :name, prompt: true, **selected %>
回答by lucapette
The problem is that you can't have an if in that position. So a first solution, though a bit ugly, is something like the following:
问题是你不能在那个位置有一个 if 。因此，第一个解决方案虽然有点难看，但类似于以下内容：
<% if @permission.role_id.nil? %>
<%= f.collection_select :role_id, roles, :id, :name, :prompt => true, {:selected => 2} %>
<% else %>
<%= f.collection_select :role_id, roles, :id, :name, :prompt => true %>
<% end %>
