Golang implementing pagination on map[string]interface{} data - go

Question

I have a json file (nested json) that I am unmarshalling its content into a map[string]interface. Now I have to implement pagination as the data is large. The client side will send as a query parameter the desired page, how can I slice the data I have?
This is a snippet of the data I am dealing with:
"packages":{
"pkg1": {
"meta": {
"description": "description1",
"name": "pkg1.1"
},
"name": "pkg1.1"
},
"pkg2": {
"meta": {
"description": "description2",
"name": "pkg2.2"
},
"name": "pkg2.2"
},
}
So what I did is that I recursively iterated through the data and created an array of a custom type containing the data I need (name, description) for each entry so that I can use it for pagination. Here is the code I used:
type Object struct {
name string
description string
}
func iterate(aMap map[string]interface{}, result *[]Object){
for key, val := range aMap {
switch val.(type) {
case map[string]interface{}:
if(key == "meta"){
switch reflect.TypeOf(val).Kind() {
case reflect.Map:
s := reflect.ValueOf(val)
var tmpData Object
if(s.MapIndex(reflect.ValueOf("name")).IsValid()){
tmpData.name = s.MapIndex(reflect.ValueOf("name")).Interface().(string)
}
if(s.MapIndex(reflect.ValueOf("description")).IsValid()){
tmpData.description = s.MapIndex(reflect.ValueOf("description")).Interface().(string)
}
*result = append(*result, tmpData)
}
}
iterate(val.(map[string]interface{}), result)
default: //DO NOTHING!!
}
}
}

Answer 1

If you're doing pagination, somewhere the data must be represented as a list instead of an object? I assume at some place in your JSON, you have a list of items, otherwise pagination doesn't make sense.
It shouldn't be very hard, something simple like this should work:
const (
itemsPerPage = 10
)
var data []map[string]interface{}
// pages start at 1, can't be 0 or less.
func GetDataPage(page int) []map[string]interface{} {
start := (page - 1) * itemsPerPage
stop := start + itemsPerPage
if start > len(data) {
return nil
}
if stop > len(data) {
stop = len(data)
}
return data[start:stop]
}

Answer 2

You are unmarshalling your json into a map which has no order by itself. In order to be able to paginate your results you need to order them in some way.
One way of doing it is to sort your data and then store it into an array. But in order to paginate you need to have ordered data and that is not possible with a map.