How to Efficiently Pass Multiple Values Between Go Templates?

Passing Multiple Values from Template to Template in Go: A Comprehensive Guide

How can I proficiently transfer multiple values from one template to another in Go? Consider the provided context:

• City struct: {ID int, Name string, Regions []Region}
• Region struct: {ID int, Name string, Shops []Destination, Masters []Master, EducationCenters []Destination}

In the main function, I execute a template cities.gohtml with a CityWithSomeData:

tpl.ExecuteTemplate(resWriter, "cities.gohtml", CityWithSomeData)

Within the template, I aim to iterate over the cities and regions to pass data to another template data:

{{range .}}
        {{$city:=.Name}}
            {{range .Regions}}
                      {{$region:=.Name}}
                      {{template "data" .Shops $city $region}}
            {{end}}
{{end}}

Solution

According to Go template documentation, the syntax for the {{template}} action allows for passing only one optional data value. To pass multiple values, we need to first encapsulate them into a single value, such as a map or a struct.

Since writing Go code within a template is not feasible, we can register a custom function to perform this task:

func Wrap(shops []Destination, cityName, regionName string) map[string]interface{} {
    return map[string]interface{}{
        "Shops":      shops,
        "CityName":   cityName,
        "RegionName": regionName,
    }
}

Custom functions are registered using Template.Funcs(). Then, we modify the template to call the Wrap() function:

{{define "data"}}
    City: {{.CityName}}, Region: {{.RegionName}}, Shops: {{.Shops}}
{{end}}
{{- range . -}}
        {{$city:=.Name}}
        {{- range .Regions -}}
              {{$region:=.Name}}
              {{- template "data" (Wrap .Shops $city $region) -}}
        {{end}}
{{- end}}

Finally, a sample code demonstrating these concepts:

t := template.Must(template.New("cities.gohtml").Funcs(template.FuncMap{
    "Wrap": Wrap,
}).Parse(src))
CityWithSomeData = [...cities]
if err := t.ExecuteTemplate(os.Stdout, "cities.gohtml", CityWithSomeData); err != nil {
    panic(err)
}

This approach allows the efficient passing of multiple values from one template to another in Go.

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