Unable to extract key/value pairs from a map obtained through YAML - go

Question

I use the goldmark-meta package to read a YAML file.
The contents I'm interested in look like this
in the YAML:
burger:
- a: ay
- b: bee
- c: see
I want to get access to both keys and values
of the returned interface, and I'm stuck.
Iterating through the return gives me a
list of the key/value pairs, but I don't
know how to obtain any info when I don't
know the key names in advance.
This program prints out the following:
func (c *config) burger() string {
// c.pageFm is type map[string]interface{}
b, ok := c.pageFm["burger"].([]interface{})
if !ok {
// No burger entry in yaml
return ""
}
debug("Burger list has %v items:\n%v", len(b), b)
debug("Type: %v", reflect.TypeOf(b))
for i := 0; i < len(b); i++ {
debug("%v", b[i])
}
return ""
}
Burger list has 3 items:
[map[a:ay] map[b:bee] map[c:see]]
Type: []interface {}
map[a:ay]
map[b:bee]
map[c:see]
How do I obtain the key and value strings?

Answer 1

In your YAML data, you have a key (burger) the value of which is a list of maps (and each map has a single key). We can iterate over the items in burger like this:
b, ok := c.pageFm["burger"].([]interface{})
if !ok {
return ""
}
for _, item := range burger {
...
}
For each item, we can iterate over available keys and values:
for _, item := range burger {
for k, v := range item.(map[interface{}]interface{}) {
...
}
}
We can convert keys and values from interface{} into string using fmt.Sprintf:
for _, item := range burger {
for k, v := range item.(map[interface{}]interface{}) {
k_str := fmt.Sprintf("%v", k)
v_str := fmt.Sprintf("%v", v)
fmt.Printf("key %s value %s\n", k_str, v_str)
}
}
Starting with the sample code from goldmark-meta, I put together this example:
package main
import (
"bytes"
"fmt"
"github.com/yuin/goldmark"
meta "github.com/yuin/goldmark-meta"
"github.com/yuin/goldmark/parser"
)
func main() {
markdown := goldmark.New(
goldmark.WithExtensions(
meta.Meta,
),
)
source := `---
burger:
- a: ay
- b: bee
- c: see
---
# Hello goldmark-meta
`
var buf bytes.Buffer
context := parser.NewContext()
if err := markdown.Convert([]byte(source), &buf, parser.WithContext(context)); err != nil {
panic(err)
}
metaData := meta.Get(context)
burger := metaData["burger"].([]interface{})
for _, item := range burger {
for k, v := range item.(map[interface{}]interface{}) {
k_str := fmt.Sprintf("%v", k)
v_str := fmt.Sprintf("%v", v)
fmt.Printf("key %s value %s\n", k_str, v_str)
}
}
}
Which outputs:
key a value ay
key b value bee
key c value see