Is it possible to have nested templates in Go using the standard library?
Google App-EngineGoTemplate EngineMustacheGoogle App-Engine Problem Overview
How do I get nested templates like Jinja has in the python runtime. TBC what I mean is how do I have a bunch of templates inherit from a base templates, just filing in blocks of the base templates, like Jinja/django-templates does. Is it possible using just html/template in the standard library.
If that is not a possibility, what are my alternatives. Mustache seems to be an option but would I then be missing out on those nice subtle features of html/template like the context sensitive escaping etc.? What other alternatives are ther?
(Environment: Google App Engin, Go runtime v1, Dev - Mac OSx lion)
Thanks for reading.
Google App-Engine Solutions
Solution 1 - Google App-Engine
Yes it is possible. A html.Template is actually a set of template files. If you execute a defined block in this set, it has access to all the other blocks defined in this set.
If you create a map of such template sets on your own, you have basically the same flexibility that Jinja / Django offers. The only difference is that the html/template package has no direct access to the file system, so you have to parse and compose the templates on your own.
Consider the following example with two different pages ("index.html" and "other.html") that both inherit from "base.html":
// Content of base.html:
{{define "base"}}<html>
<head>{{template "head" .}}</head>
<body>{{template "body" .}}</body>
</html>{{end}}
// Content of index.html:
{{define "head"}}<title>index</title>{{end}}
{{define "body"}}index{{end}}
// Content of other.html:
{{define "head"}}<title>other</title>{{end}}
{{define "body"}}other{{end}}
And the following map of template sets:
tmpl := make(map[string]*template.Template)
tmpl["index.html"] = template.Must(template.ParseFiles("index.html", "base.html"))
tmpl["other.html"] = template.Must(template.ParseFiles("other.html", "base.html"))
You can now render your "index.html" page by calling
tmpl["index.html"].Execute("base", data)
and you can render your "other.html" page by calling
tmpl["other.html"].Execute("base", data)
With some tricks (e.g. a consistent naming convention of your template files), it's even possible to generate the tmpl map automatically.
Solution 2 - Google App-Engine
note, when you execute your base template, you must pass values down to the child templates, here I simply pass ".", so that everything is passed down.
template one displays {{.}}
{{define "base"}}
<html>
<div class="container">
{{.}}
{{template "content" .}}
</div>
</body>
</html>
{{end}}
template two displays {{.domains}} that's passed into the parent.
{{define "content"}}
{{.domains}}
{{end}}
Note, if we used {{template "content" .}} instead of {{template "content" .}}, .domains wouldn't be accessible from the content template.
DomainsData := make(map[string]interface{})
DomainsData["domains"] = domains.Domains
if err := groupsTemplate.ExecuteTemplate(w, "base", DomainsData); err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
}
Solution 3 - Google App-Engine
having worked with other template packages, now a days I mostly work with standard html/template package, I guess I was naive to not appreciate the simplicity it provides and other goodies. I use a very similar approach to accepted answer with following changes
you don't need to wrap your layouts with additional base template, a template block is created for every parsed file so in this case it is redundant, I also like to use the block action provided in new version of go, which allows you to have default block content in case you don't provide one in child templates
// base.html
<head>{{block "head" .}} Default Title {{end}}</head>
<body>{{block "body" .}} default body {{end}}</body>
and you page templates can be the same as
// Content of index.html:
{{define "head"}}<title>index</title>{{end}}
{{define "body"}}index{{end}}
// Content of other.html:
{{define "head"}}<title>other</title>{{end}}
{{define "body"}}other{{end}}
now to execute the templates you need to call it like so
tmpl["index.html"].ExecuteTemplate(os.Stdout, "base.html", data)
Solution 4 - Google App-Engine
Use Pongo, which is a super-set of Go Templates that supports the {{extends}} and {{block}} tags for template inheritance, just like Django.
Solution 5 - Google App-Engine
I've been coming back to this answer for days, finally bit the bullet and wrote a small abstraction layer / pre processor for this. It basically:
- Adds the 'extends' keyword to templates.
- Allows overriding 'define' calls (thus default values for greggory are possible)
- Allows non defined 'template' calls, they just give an empty string
- Sets the default value of . in 'template' calls to . of the parent