Show default content in a template if an object is nil otherwise show based on the set property

问题

In my template, I would like to include some default meta tags (90% of the time). However, when a specific property is set, I would like to show a different set of text.

I know I can set an anonymous struct and set a property with either "default" or "some-x". However, this means, I need to add an anonymous struct to 90% of my handlers that just currently pass nil.

Is there way to do something like

{{if eq . nil}} 
   // default meta tag
{{else if eq .MetaValue "some-x"}} 
   //other
{{end}}

If I try something like my above code, it compiles but doesn't do what I want. Appreciate any suggestions on how to handle it properly without adding a lot of boiler plate.

Thanks!

回答1:

{{if not .}}
   output when . is nil or otherwise empty including
     false, 0, and any array, slice, map, or string of length zero
{{else if eq .MetaValue "some-x"}}
       // some-x case
{{else}} 
       // other case
{{end}}

回答2:

I've been recently facing an issue with identifying nil vs 0 values in a Helm Chart (which uses Go templates, including sprig) and haven't found any solutions posted, so I thought I'd add mine here.

I came up with a kind of ugly solution which is to quote the value and then check for a string that matches "<nil>" (with quotes, so you'd actually be checking (quote .Values.thing | eq "\"<nil>\"")). This allows differentiating tests against empty values vs defined 0 values. In my case, I was trying to build a config file where some default options were non-0, so when 0 was explicitly set, I wanted to know that 0 was set instead of just omitted.

Hopefully this can be a help to someone else.

It would be nice to have a better way to do this, but so far I haven't found anything that doesn't require creating and adding my own template functions.

来源：https://stackoverflow.com/questions/32774234/show-default-content-in-a-template-if-an-object-is-nil-otherwise-show-based-on-t

标签

go-templates