How to Flatten Nested JSON Structures in Go Using Custom UnmarshalJSON Functions?

Flattening Nested JSON

Navigating complex JSON structures with multiple levels of nesting can be challenging in Go. When it becomes necessary to flatten these nested structures into a more streamlined format, custom solutions are often needed.

In the presented scenario, the task is to flatten a JSON response that contains a nested Social type with a further nested Facebook type. The goal is to eliminate the intermediate Facebook type and flatten its properties into the Social type.

Custom UnmarshalJSON Functions

To achieve this, we can utilize the power of Go's UnmarshalJSON function, which allows you to customize how JSON is decoded into a struct. Here's how to implement this for flattening nested JSON:

<code class="go">type Social struct {
    // ... existing properties ...
    FacebookLikes       uint32 `json:"-"`
    FacebookShares      uint32 `json:"-"`
    FacebookComments    uint32 `json:"-"`
    FacebookTotal       uint32 `json:"-"`
}

func (s *Social) UnmarshalJSON(data []byte) error {
    m := make(map[string]interface{})
    if err := json.Unmarshal(data, &m); err != nil {
        return err
    }

    m = Flatten(m)

    // Extract nested Facebook properties
    if fbMap, ok := m["Facebook"].(map[string]interface{}); ok {
        s.FacebookLikes = fbMap["FacebookLikes"].(uint32)
        s.FacebookShares = fbMap["FacebookShares"].(uint32)
        s.FacebookComments = fbMap["FacebookComments"].(uint32)
        s.FacebookTotal = fbMap["FacebookTotal"].(uint32)
    }

    return nil
}</code>

Flatten Helper Function

The Flatten helper function is responsible for removing nested maps and replacing them with dot-delimited keys:

<code class="go">func Flatten(m map[string]interface{}) map[string]interface{} {
    o := make(map[string]interface{})
    for k, v := range m {
        switch child := v.(type) {
        case map[string]interface{}:
            nm := Flatten(child)
            for nk, nv := range nm {
                o[k+"."+nk] = nv
            }
        default:
            o[k] = v
        }
    }
    return o
}</code>

Using this approach, the nested Facebook type is removed, and its properties are flattened into the Social type, resulting in a more concise and manageable data structure.

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