如何以通用方式引用嵌套地图

Question

I'm trying to access a nested field like the services key for example from a yaml file I unmarshalled. For what it's worth I don't want to have to build a struct that reflects the structure of the yaml file since it may not always take this form. The yaml file looks like the following:

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

The code looks like this

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

I think your intent is to use a mapping for applications. If so, delete the "-" following the text "applications:":

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

Access the applications field as a map[interface{}]interface{}:

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

A good way to debug issues like this is to print the value with "%#v":

fmt.Printf("%#v
", 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"}