How can I flatten nested JSON data into a single level structure using custom UnmarshalJSON functions in Go?

Flattening Nested JSON

Flattening nested JSON data into a single level structure is a common task in data processing. Here's how you can achieve this in Go using a custom UnmarshalJSON function:

UnmarshalJSON Function

Custom UnmarshalJSON functions allow Go structs to handle the unmarshalling of JSON data. Here's your updated Social struct with the UnmarshalJSON implementation:

<code class="go">type Social struct {
    GooglePlusPlusOnes  uint32 `Social:"GooglePlusOne"`
    TwitterTweets       uint32 `json:"Twitter"`
    LinkedinShares      uint32 `json:"LinkedIn"`
    PinterestPins       uint32 `json:"Pinterest"`
    StumbleuponStumbles uint32 `json:"StumbleUpon"`
    DeliciousBookmarks  uint32 `json:"Delicious"`

    // Custom unmarshalling for the Facebook fields
    FacebookLikes       uint32 `json:"-"`
    FacebookShares      uint32 `json:"-"`
    FacebookComments    uint32 `json:"-"`
    FacebookTotal       uint32 `json:"-"`
}

// UnmarshalJSON implements the Unmarshaler interface for custom JSON unmarshalling
func (s *Social) UnmarshalJSON(data []byte) error {
    type FacebookAlias Facebook
    aux := &struct {
        Facebook FacebookAlias `json:"Facebook"`
    }{}

    if err := json.Unmarshal(data, aux); err != nil {
        return err
    }

    s.FacebookLikes = aux.Facebook.FacebookLikes
    s.FacebookShares = aux.Facebook.FacebookShares
    s.FacebookComments = aux.Facebook.FacebookComments
    s.FacebookTotal = aux.Facebook.FacebookTotal
    return nil
}</code>

Usage

With the updated Social struct, you can now unmarshal your JSON document and flatten it:

<code class="go">package main

import (
    "encoding/json"
    "fmt"
)

type Social struct {
    // ... (same as before)
}

func (s *Social) UnmarshalJSON(data []byte) error { // ... (same as before) }

func main() {
    var jsonBlob = []byte(`[
        {"StumbleUpon":0,"Reddit":0,"Facebook":{"commentsbox_count":4691,"click_count":0,"total_count":298686,"comment_count":38955,"like_count":82902,"share_count":176829},"Delicious":0,"GooglePlusOne":275234,"Buzz":0,"Twitter":7346788,"Diggs":0,"Pinterest":40982,"LinkedIn":0}
    ]`)

    var social []Social
    err := json.Unmarshal(jsonBlob, &social)
    if err != nil {
        fmt.Println("error:", err)
    }
    fmt.Printf("%+v", social)
}</code>

This code will output your desired flattened JSON structure, with Facebook fields merged into the top-level Social struct.

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