How to pass multiple data to Go template?

Question

I want to pass two data objects to Go Template. One is a MongoDB query result and other is an integer array.

MongoDB Query:-

var results []User
sess, db := GetDatabase()
defer sess.Close()
c := db.C("user")
err := c.Find(nil).All(&results)

I want to sent 'result' and an int array through following code

GetTemplate("list").Execute(w,???????)

If there is only db result, we could use it as

GetTemplate("list").Execute(w,results)

and in template we could access it {{.Name}} etc. (where Name is a struct field of []User)

Please tell me how to pass these data and how to access them in template.

Answer 1

You may only pass a single value, but that value may be a composed value of multiple values, e.g. a struct, map or slice. So simply wrap your multiple data intended for the template in a struct or in a map.

Example with a struct:

type Data struct {
    Results []User // Must be exported!
    Other   []int  // Must be exported!
}

data := &Data{results, []int{1, 2, 3}}
if err := GetTemplate("list").Execute(w, data); err != nil {
    // Handle error
}

Also note that a new, named type is not required, you could also use an anonymous struct literal, which could look like this:

data := struct {
    Results []User // Must be exported!
    Other   []int  // Must be exported!
}{results, []int{1, 2, 3}}

Example with a map:

m := map[string]interface{}{
    "Results": results,
    "Other":   []int{1, 2, 3},
}

if err := GetTemplate("list").Execute(w, m); err != nil {
    // Handle error
}

Note that using a map, it is not required to use capitalized strings as keys, e.g. you could've used "results" and "other" too (but in my opinion it's better to use keys with capital starting letters, should you move to struct sometimes in the future, you would have less corrections to make).

In both cases you may refer to the []User results with {{.Results}} and to the additional int slice with {{.Other}}.

So for example to range over the users:

{{range .Results}}
    User name:{{.Name}}
{{end}}

Example with a slice:

s := []interface{}{
    results,
    []int{1, 2, 3},
}

if err := GetTemplate("list").Execute(w, s); err != nil {
    // Handle error
}

This is less readable, but a viable solution. In the template you have to index the template data to get the "individual" values, e.g.:

{{range index . 0}}
    User name:{{.Name}}
{{end}}

Other: {{index . 1}}

Try it on the Go Playground.

Other ways...

There are other "theoretical" ways too, but I wouldn't use them just because it works.

For example, you could also pass in a channel from which receives would provide the values.

Yet another solution could be to register custom functions which when called would return the values.