Usage of variables in a nested template which is also defined as a variable in a go template?

huangapple
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英文:

Usage of variables in a nested template which is also defined as a variable in a go template?

问题

  1. package main
  3. import (
  4. 	"os"
  5. 	"text/template"
  6. )
  8. type Todo struct {
  9. 	Name        string
  10. 	Description string
  11. 	Subtemplate string
  12. }
  14. func main() {
  15. 	td := Todo{
  16. 		Name:        "Test name",
  17. 		Description: "Test description",
  18. 		Subtemplate: "Subtemplate {{.Name}}",
  19. 	}
  21. 	t, err := template.New("todos").Parse(`{{template "subtemplate" .}} You have a task named "{{ .Name}}" with description: "{{ .Description}}"`)
  22. 	if err != nil {
  23. 		panic(err)
  24. 	}
  26. 	// Define the subtemplate
  27. 	_, err = t.New("subtemplate").Parse(td.Subtemplate)
  28. 	if err != nil {
  29. 		panic(err)
  30. 	}
  32. 	err = t.Execute(os.Stdout, td)
  33. 	if err != nil {
  34. 		panic(err)
  35. 	}
  36. }

上述代码的结果是：

Subtemplate Test name You have a task named "Test name" with description: "Test description"

这意味着子模板中的变量.Name没有被解析（可能是因为设计上不可能，需要一种递归调用的方式）。有没有其他方法可以实现这个效果？

对于使用template.FuncMap定义的模板函数也应该适用。谢谢。

英文:

The idea is to define a variable for a go template which is also a template using variables (a nested template) like this:

  1. package main
  3. import (
  4. 	"os"
  5. 	"text/template"
  6. )
  8. type Todo struct {
  9. 	Name        string
  10. 	Description string
  11. 	Subtemplate string
  12. }
  14. func main() {
  15. 	td := Todo{
  16. 		Name: "Test name",
  17. 		Description: "Test description",
  18. 		Subtemplate: "Subtemplate {{.Name}}",
  19. 	}
  21. 	t, err := template.New("todos").Parse("{{.Subtemplate}} You have a task named \"{{ .Name}}\" with description: \"{{ .Description}}\"")
  22. 	if err != nil {
  23. 		panic(err)
  24. 	}
  25. 	err = t.Execute(os.Stdout, td)
  26. 	if err != nil {
  27. 		panic(err)
  28. 	}
  29. }

The result of the code above is however:

Subtemplate {{.Name}} You have a task named "Test name" with description: "Test description"

means the variable .Name in the subtemplate is not resolved (probably by design not possible, would require some kind of a recursive call). Is there any/other way to achieve this effect?

It should work for the template functions defined using template.FuncMap too. Thanx.

答案1

得分: 2

你可以注册一个函数来解析字符串模板并执行它。

该函数可以像这样：

  1. func exec(body string, data interface{}) (string, error) {
  2.     t, err := template.New("").Parse(body)
  3.     if err != nil {
  4.         return "", err
  5.     }
  6.     buf := &strings.Builder{}
  7.     err = t.Execute(buf, data)
  8.     return buf.String(), err
  9. }

你将模板主体文本和用于模板执行的数据传递给它。它会执行并返回结果。

一旦注册，你可以在模板中这样调用它：

  1. {{exec .Subtemplate .}}

完整示例：

  1. td := Todo{
  2.     Name:        "Test name",
  3.     Description: "Test description",
  4.     Subtemplate: "Subtemplate {{.Name}}",
  5. }
  7. t, err := template.New("todos").Funcs(template.FuncMap{
  8.     "exec": func(body string, data interface{}) (string, error) {
  9.         t, err := template.New("").Parse(body)
  10.         if err != nil {
  11.             return "", err
  12.         }
  13.         buf := &strings.Builder{}
  14.         err = t.Execute(buf, data)
  15.         return buf.String(), err
  16.     },
  17. }).Parse("{{exec .Subtemplate .}} You have a task named \"{{ .Name}}\" with description: \"{{ .Description}}\"")
  18. if err != nil {
  19.     panic(err)
  20. }
  21. err = t.Execute(os.Stdout, td)
  22. if err != nil {
  23.     panic(err)
  24. }

这将输出（在Go Playground上尝试）：

  1. Subtemplate Test name You have a task named "Test name" with description: "Test description"

请注意，如果子模板在运行时不会更改，你应该预先解析它并将生成的模板（*template.Template）存储起来，以避免每次执行模板时都进行解析。

英文:

You can register a function which parses a string template and executes it.

The function could look like this:

  1. func exec(body string, data any) (string, error) {
  2.     t, err := template.New("").Parse(body)
  3.     if err != nil {
  4.         return "", err
  5.     }
  6.     buf := &strings.Builder{}
  7.     err = t.Execute(buf, data)
  8.     return buf.String(), err
  9. }

You pass the template body text and the data for template execution to it. It executes it and returns the result.

Once registered, you can call it like this from a template:

  1. {{exec .Subtemplate .}}

Full example:

  1. td := Todo{
  2. 	Name:        "Test name",
  3. 	Description: "Test description",
  4. 	Subtemplate: "Subtemplate {{.Name}}",
  5. }
  7. t, err := template.New("todos").Funcs(template.FuncMap{
  8. 	"exec": func(body string, data any) (string, error) {
  9. 		t, err := template.New("").Parse(body)
  10. 		if err != nil {
  11. 			return "", err
  12. 		}
  13. 		buf := &strings.Builder{}
  14. 		err = t.Execute(buf, data)
  15. 		return buf.String(), err
  16. 	},
  17. }).Parse("{{exec .Subtemplate .}} You have a task named \"{{ .Name}}\" with description: \"{{ .Description}}\"")
  18. if err != nil {
  19. 	panic(err)
  20. }
  21. err = t.Execute(os.Stdout, td)
  22. if err != nil {
  23. 	panic(err)
  24. }

This will output (try it on the Go Playground):

  1. Subtemplate Test name You have a task named "Test name" with description: "Test description"

Note that if the subtemplate does not change during runtime, you should pre-parse it and store the resulting template (*template.Template) to avoid having to parse it each time you execute the template.

答案2

得分: 1

如果你不介意性能问题，你可以渲染两次...

  1. package main
  3. import (
  4.     "os"
  5.     "text/template"
  6.     "bytes"
  7. )
  9. type Todo struct {
  10.     Name        string
  11.     Description string
  12.     Subtemplate string
  13. }
  15. func main() {
  16.     td := Todo{
  17.         Name:        "测试名称",
  18.         Description: "测试描述",
  19.         Subtemplate: "子模板 {{.Name}}",
  20.     }
  22.     t, err := template.New("todos").Parse("{{.Subtemplate}} 你有一个名为“{{.Name}}”的任务，描述为：“{{.Description}}”")
  23.     if err != nil {
  24.         panic(err)
  25.     }
  26.     buffer := &bytes.Buffer{}
  27.     err = t.Execute(buffer, td)
  28.     tc, err := template.New("todo2").Parse(string(buffer.Bytes()))
  29.     if err != nil {
  30.         panic(err)
  31.     }
  32.     err = tc.Execute(os.Stdout, td)
  33.     if err != nil {
  34.         panic(err)
  35.     }
  36. }
英文:

You can render twice if you don't mind for peformance ...

  1. package main
  3. import (
  4.     "os"
  5.     "text/template"
  6.     "bytes"
  7. )
  9. type Todo struct {
  10.     Name        string
  11.     Description string
  12.     Subtemplate string
  13. }
  15. func main() {
  16.     td := Todo{
  17.         Name: "Test name",
  18.         Description: "Test description",
  19.         Subtemplate: "Subtemplate {{.Name}}",
  20.     }
  22.     t, err := template.New("todos").Parse("{{.Subtemplate}} You have a task named \"{{ .Name}}\" with description: \"{{ .Description}}\"")
  23.     if err != nil {
  24.         panic(err)
  25.     }
  26.     buffer := &bytes.Buffer{}
  27.     err = t.Execute(buffer, td)
  28.     tc, err := template.New ("todo2").Parse(string (buffer.Bytes ()))
  29.     if err != nil {
  30.         panic (err)
  31.     }
  32.     err = tc.Execute(os.Stdout, td)
  33.     if err != nil {
  34.         panic(err)
  35.     }
  36. }

huangapple
  • 本文由 发表于 2023年1月10日 15:48:34
  • 转载请务必保留本文链接：https://go.coder-hub.com/75066909.html
  • go
  • go-templates
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