go - 如何以通用方式引用嵌套 map

Question

我正在尝试从我解码的 yaml 文件访问嵌套字段，例如 services 键。对于它的值(value)，我不想构建一个反射(reflect) yaml 文件结构的 struct，因为它可能并不总是采用这种形式。 yaml 文件如下所示:

declared-services:
    Cloudant:
        label: cloudantNoSQLDB
        plan: Lite
applications:
- name: myProject
  memory: 512M
  instances: 1
  random-route: true
  buildpack: java
  services:
  - Cloudant
  timeout: 180
env:
  services_autoconfig_excludes: cloudantNoSQLDB=config

代码是这样的

import "gopkg.in/yaml.v2"

func getManifestConfig() *Manifest {
    wd, _ := os.Getwd()
    manPath := wd + "/JavaProject/" + manifest
    var man map[string]interface{}
    f, err := ioutil.ReadFile(manPath)
    if err != nil {
        e(err) //irrelevant method that prints error messages
    }

    yaml.Unmarshal(f, &man)
    fmt.Println(man["applications"]) //This will print all the contents under applications 
    fmt.Println(man["applications"].(map[string]interface{})["services"]) //panic: interface conversion: interface {} is []interface {}, not map[string]interface {}
    return nil
}

Answer 1

我认为您的意图是为应用程序 使用映射。如果是这样，请删除文本“应用程序:”后面的“-”:

declared-services:
    Cloudant:
        label: cloudantNoSQLDB
        plan: Lite
applications:
  name: myProject
  memory: 512M
  instances: 1
  random-route: true
  buildpack: java
  services:
  - Cloudant
  timeout: 180
env:
  services_autoconfig_excludes: cloudantNoSQLDB=config

作为 map[interface{}]interface{} 访问 applications 字段:

fmt.Println(man["applications"].(map[interface{}]interface{})["services"])

调试此类问题的一个好方法是使用“%#v”打印值:

fmt.Printf("%#v\n", man["applications"])
// output with the "-"
// []interface {}{map[interface {}]interface {}{"buildpack":"java", "services":[]interface {}{"Cloudant"}, "timeout":180, "name":"myProject", "memory":"512M", "instances":1, "random-route":true}}

// output without the "-":
// map[interface {}]interface {}{"instances":1, "random-route":true, "buildpack":"java", "services":[]interface {}{"Cloudant"}, "timeout":180, "name":"myProject", "memory":"512M"}