如何设置默认选择选项以使用Golang选择标签？

Question

First, I have found this question:

How can I set the default value for an HTML <select> element in Golang?

But in my case I don't know how to do.

I have many posts data and render them to template.

Controller:

c.Data["posts"] = posts_data

View:

{{ range $post := .posts }}
<option value="{{ $post.ID }}">{{ $post.Name }}</option>
{{ end }}

Works fine.

But if change to:

Controller:

c.Data["posts"] = posts_data
c.Data["post_id"] = param_data

View:

{{ range $post := .posts }}
<option value="{{ $post.ID }}" {{ if eq $post.ID .post_id }}selected="selected"{{ end }}>{{ $post.Name }}</option>
{{ end }}

Got error:

template Execute err: template: posts/index.tpl:20:70: executing "posts/index.tpl" at <.post_id>: can't evaluate field post_id in type models.Post

It's true that post_id doesn't exists in models.Post. But how to use it in this way?

Answer 1

The range command sets . to the current value. Use $ to refer to the root value passed to the template:

{{ range $post := .posts }}
<option value="{{ $post.ID }}" {{ if eq $post.ID $.post_id }}selected="selected"{{ end }}>{{ $post.Name }}</option>
{{ end }}

Because range sets ., the template can be simplified to:

{{ range $post := .posts }}
<option value="{{ .ID }}" {{ if eq .ID $.post_id }}selected="selected"{{ end }}>{{ .Name }}</option>
{{ end }}