如何从FieldDescriptor和protoreflect.Range中获取字段值？

huangapple
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英文:

How to get a field value from FieldDescriptor and Value in protoreflect.Range?

问题

我有一个proto定义：

  1. message Foo {
  2.   oneof bar {
  3.     BarA bar_a = 1;
  4.     BarB bar_b = 2;
  5.   }
  6. }
  8. message BarA {
  9.   string text = 1;
  10. }
  12. message BarB {
  13.   int32 num = 1;
  14. }

然后是代码：

  1. foo := &Foo{
  2.     Bar: &Foo_BarA{
  3.         BarA: &BarA{
  4.             Text: "text",
  5.         },
  6.     },
  7. }
  8. md := foo.ProtoReflect()
  9. md.Range(func(fd protoreflect.FieldDescriptor, v protoreflect.Value) bool {
  11. }

在md.Range中，如何从fd, v对中获取字段值？例如，当迭代Bar字段时，我想获取一个BarA对象并检索text。我需要使用Range，因为我还在使用FieldOptions。

更新更多信息

我实际上正在使用的第一个proto是：

  1. extend google.protobuf.FieldOptions {
  2.   string field_name = 50000;
  3. }
  5. extend google.protobuf.MessageOptions {
  6.   string template_name = 50000;
  7.   Type type = 50001;
  8. }
  10. message SendNotificationRequest {
  11.   Type type = 1;
  12.   Template template = 2;
  13. }
  15. enum Type {
  16.   TYPE_UNSPECIFIED = 0;
  17.   TYPE_EMAIL = 1;
  18.   TYPE_PUSH = 2;
  19. }
  21. message Template {
  22.   oneof template {
  23.     EmailTemplate email_template = 1;
  24.     PushTemplate push_template = 2;
  25.   }
  26. }
  28. message EmailTemplate {
  29.   option (type) = TYPE_EMAIL;
  31.   oneof template {
  32.     WelcomeEmailTemplate welcome_email_template = 1;
  33.   }
  34. }
  36. message WelcomeEmailTemplate {
  37.   option (template_name) = "welcome_email";
  39.   Field title = 1 [(field_name) = "main_title"];
  40.   Field user_name = 2 [(field_name) = "name"];
  41. }
  43. message Field {
  44.   oneof value {
  45.     string str = 1;
  46.     bool bool = 2;
  47.     int64 num = 3;
  48.   }
  49. }

我的第二个proto是另一个服务+项目的一部分：

  1. message CreateNotificationRequest {
  2.   Type type = 1;
  3.   string template_name = 2;
  4.   map<string, Field> template_fields = 2; 
  5. }
  7. enum Type {
  8.   TYPE_UNSPECIFIED = 0;
  9.   TYPE_EMAIL = 1;
  10.   TYPE_PUSH = 2;
  11. }
  13. message Field {
  14.   oneof value {
  15.     string str = 1;
  16.     bool bool = 2;
  17.     int64 num = 3;
  18.   }
  19. }

我想编写一个函数，可以将任何SendNotificationRequest转换为CreateNotificationRequest。让我们将SendNotificationRequest的导入别名称为api，CreateNotificationRequest的别名称为api2。我不能更改api2。

虽然不太相关，但我做出了一个非必需的决定，即在我的服务(api)中使用了类型化的Template，而不是api2的通用映射，因为我认为类型化的类更易于维护且更不容易出错。

对于一个示例转换，这个：

  1. &api.SendNotificationRequest{
  2.     Type: api.Type_TYPE_EMAIL,
  3.     Template:   &api.Template {
  4.         Template: &api.Template_EmailTemplate{
  5.             EmailTemplate: &api.EmailTemplate{
  6.                 Template: &api.EmailTemplate_WelcomeEmailTemplate{
  7.                     Title:     &api.Field{Value: &api.Placeholder_Str{Text: "Welcome Bob"}},
  8.                     UserName:     &api.Field{Value: &api.Placeholder_Str{Text: "Bob Jones"}},
  9.                 },
  10.             },
  11.         },
  12.     },
  13. }

应该转换为：

  1. &api2.CreateNotificationRequest{
  2.     Type: api2.Type_TYPE_EMAIL,
  3.     TemplateName: "welcome_email",
  4.     Template:   map[string]*api2.Field{
  5.         "main_title":     &api2.Field{Value: &api.Placeholder_Str{Text: "Welcome Bob"}},
  6.         "name":     &api2.Field{Value: &api.Placeholder_Str{Text: "Bob Jones"}},
  7.     },
  8. }

可能会有新的EmailTemplate的oneof，以及像WelcomeEmailTemplate这样的模板可能会更改其字段。但我想编写一个不需要针对这些更改进行更新的函数。

我相信这是可能的，参考这里的答案。

我可以在SendNotificationRequest及其字段上嵌套md.Range，以处理所有字段，并编写一个switch case来转换任何Field的oneof。我还可以获取FieldOption和MessageOption。在此过程中，我构建CreateNotificationRequest。

英文:

I have a proto:

  1. message Foo {
  2. oneof bar {
  3. BarA bar_a = 1;
  4. BarB bar_b = 2;
  5. }
  6. }
  7. message BarA {
  8. string text = 1;
  9. }
  10. message BarB {
  11. int num = 1;
  12. }

Then the code:

  1. foo = &amp;Foo{
  2. Bar: &amp;Foo_BarA{
  3. BarA: &amp;BarA{
  4. Text: &quot;text&quot;,
  5. },
  6. },
  7. }
  8. md := foo.ProtoReflect()
  9. md.Range(func(fd protoreflect.FieldDescriptor, v protoreflect.Value) bool {
  10. }

Inside md.Range, how do I get the field value from the fd, v pair? For example when it iterates over the Bar field, I want to get a BarA object and retrieve text. I need to use Range because I'm also using FieldOptions.

Update with more info

My first proto is that I'm actually working with (the above protos are contrived examples) is:

  1. extend google.protobuf.FieldOptions {
  2. string field_name = 50000;
  3. }
  4. extend google.protobuf.MessageOptions {
  5. string template_name = 50000;
  6. Type type = 50001;
  7. }
  8. message SendNotificationRequest {
  9. Type type = 1;
  10. Template template = 2;
  11. }
  12. enum Type {
  13. TYPE_UNSPECIFIED = 0;
  14. TYPE_EMAIL = 1;
  15. TYPE_PUSH = 2;
  16. }
  17. message Template {
  18. oneof template {
  19. EmailTemplate email_template = 1;
  20. PushTemplate push_template = 2;
  21. }
  22. }
  23. message EmailTemplate {
  24. option (type) = TYPE_EMAIL;
  25. oneof template {
  26. WelcomeEmailTemplate welcome_email_template = 1;
  27. }
  28. }
  29. message WelcomeEmailTemplate {
  30. option (template_name) = &quot;welcome_email&quot;;
  31. Field title = 1 [(field_name) = &quot;main_title&quot;];
  32. Field user_name = 2 [(field_name) = &quot;name&quot;];
  33. }
  34. message Field {
  35. oneof value {
  36. string str = 1;
  37. bool bool = 2;
  38. int64 num = 3;
  39. }
  40. }

My second proto, part of another service+project, is:

  1. message CreateNotificationRequest {
  2. Type type = 1;
  3. string template_name = 2;
  4. map&lt;string, Field&gt; template_fields = 2; 
  5. }
  6. enum Type {
  7. TYPE_UNSPECIFIED = 0;
  8. TYPE_EMAIL = 1;
  9. TYPE_PUSH = 2;
  10. }
  11. message Field {
  12. oneof value {
  13. string str = 1;
  14. bool bool = 2;
  15. int64 num = 3;
  16. }
  17. }

I want to write one function that can convert any SendNotificationRequest to a CreateNotificationRequest. Let's call SendNotificationRequest's import alias api and CreateNotificationRequest's api2. I cannot change api2.

Not too relevant but I made the non-required decision to use typed Template for my service (api) instead of the generic map of api2, as I felt typed classes are more maintainable and less error-prone.

For an example conversion, this

  1. &amp;api.SendNotificationRequest{
  2. Type: api.Type_TYPE_EMAIL,
  3. Template:   &amp;api.Template {
  4. Template: &amp;api.Template_EmailTemplate{
  5. EmailTemplate: &amp;api.EmailTemplate{
  6. Template: &amp;api.EmailTemplate_WelcomeEmailTemplate{
  7. Title:     &amp;api.Field{Value: &amp;api.Placeholder_Str{Text: &quot;Welcome Bob&quot;}},
  8. UserName:     &amp;api.Field{Value: &amp;api.Placeholder_Str{Text: &quot;Bob Jones&quot;}},
  9. },
  10. },
  11. },
  12. },
  13. }

should convert to:

  1. &amp;api2.CreateNotificationRequest{
  2. Type: api2.Type_TYPE_EMAIL,
  3. TemplateName: &quot;welcome_email&quot;,
  4. Template:   map[string]*api2.Field{
  5. &quot;main_title&quot;:     &amp;api2.Field{Value: &amp;api.Placeholder_Str{Text: &quot;Welcome Bob&quot;}},
  6. &quot;name&quot;:     &amp;api2.Field{Value: &amp;api.Placeholder_Str{Text: &quot;Bob Jones&quot;}},
  7. },
  8. }

There may be new oneofs of EmailTemplate, and templates like WelcomeEmailTemplate may change its fields. But I want to write one function that doesn't need to be updated for those changes.

I believe this is very possible from the answer here.

I can nest md.Range on a SendNotificationRequest and its fields to process all its fields, and write a switch case to convert any Field oneof. I can also fetch FieldOption and MessageOption. While this happens, I build the CreateNotificationRequest.

答案1

得分: 2

你可以使用以下代码获取BarA的值：

  1. md.Range(func(fd protoreflect.FieldDescriptor, v protoreflect.Value) bool {
  2.     w := v.Message().Get(fd.Message().Fields().ByNumber(1))
  3.     fmt.Println(w) // 输出"text"
  4.     return false
  5. })

这段代码可以直接工作，因为你的 proto 消息只有一个已填充的字段（bar_a）。如果你有更多已填充的字段，你应该添加更多的检查。例如，检查当前的 FieldDescriptor 是否是你要查找的字段。一个更健壮的实现可能如下所示：

  1. md.Range(func(fd protoreflect.FieldDescriptor, v protoreflect.Value) bool {
  2.     if fd.Name() == "bar_a" {
  3.         if field := fd.Message().Fields().ByName("text"); field != nil {
  4.             w := v.Message().Get(field)
  5.             fmt.Println(w) // 输出"text"
  6.             return false
  7.         }
  8.     }
  9.     return true
  10. })

使用 ByName 而不是 ByNumber 是有争议的，因为字段名在序列化中并不起作用，但在我看来，它可以使代码更易读。

作为另一种选择，你可以通过对 v 中持有的接口进行类型断言来直接获取字段的具体值：

  1. md.Range(func(fd protoreflect.FieldDescriptor, v protoreflect.Value) bool {
  2.     if barA, ok := v.Message().Interface().(*BarA); ok {
  3.         fmt.Println(barA.Text)
  4.         return false
  5.     }
  6.     return true
  7. })
英文:

You can get the value of BarA with:

  1. 	md.Range(func(fd protoreflect.FieldDescriptor, v protoreflect.Value) bool {
  2. 		w := v.Message().Get(fd.Message().Fields().ByNumber(1))
  3. 		fmt.Println(w) // prints &quot;text&quot;
  4. 		return false
  5. 	})

This works straight away because your proto message has only one populated field (bar_a). If you have more populated fields, you should add more checks. E.g. check that the current FieldDescriptor is the one you are looking for. A more robust implementation might look like:

  1. 	md.Range(func(fd protoreflect.FieldDescriptor, v protoreflect.Value) bool {
  2. if fd.Name() == &quot;bar_a&quot; {
  3. if field := fd.Message().Fields().ByName(&quot;text&quot;); field != nil {
  4. w := v.Message().Get(field)
  5. fmt.Println(w) // text
  6. return false
  7. }
  8. }
  9. return true
  10. })

Using ByName instead of ByNumber is debatable, since the field name doesn't play a role in the serialization, but IMO it makes for more readable code.

<hr>

As an alternative, you can directly get the concrete value of the field by type-asserting the interface held in v:

  1. md.Range(func(fd protoreflect.FieldDescriptor, v protoreflect.Value) bool {
  2. if barA, ok := v.Message().Interface().(*BarA); ok {
  3. fmt.Println(barA.Text)
  4. return false
  5. }
  6. return true
  7. })

huangapple
  • 本文由 发表于 2021年9月11日 10:17:32
  • 转载请务必保留本文链接：https://go.coder-hub.com/69139530.html
  • go
  • protocol-buffers
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