How to Efficiently Convert a Go Struct to a Map Using JSON Tags?

Function for Converting a Struct to a Map in Golang

Question:

How can I efficiently convert a struct to a map in Golang, utilizing JSON tags as keys where possible?

Answer:

Third-Party Library:

The structs package by Fatih provides a straightforward and comprehensive solution for this task:

func Map(object interface{}) map[string]interface{}

Usage:

package main

import (
    "fmt"

    "github.com/fatih/structs"
)

type Server struct {
    Name    string `json:"name"`
    ID      int32  `json:"id"`
    Enabled bool   `json:"enabled"`
}

func main() {
    s := &Server{
        Name:    "gopher",
        ID:      123456,
        Enabled: true,
    }

    m := structs.Map(s)
    fmt.Println(m) // Output: {"name":"gopher", "id":123456, "enabled":true}
}

Features:

• Supports anonymous and nested structs
• Uses JSON tags for keys
• Allows filtering of fields using tags

Custom Implementation:

If a custom implementation is preferred, reflect.Struct can be utilized:

func ConvertToMap(model interface{}) map[string]interface{} {
    // Get the reflect type and value of the model
    modelType := reflect.TypeOf(model)
    modelValue := reflect.ValueOf(model)
    
    if modelValue.Kind() == reflect.Ptr {
        modelValue = modelValue.Elem()
    }
    
    // Check if the model is a struct
    if modelType.Kind() != reflect.Struct {
        return nil
    }
    
    // Create a new map to store the key-value pairs
    ret := make(map[string]interface{})
    
    // Iterate over the fields of the struct
    for i := 0; i < modelType.NumField(); i++ {
        // Get the field and its name
        field := modelType.Field(i)
        fieldName := field.Name
        
        // Check if the field has a JSON tag
        jsonTag := field.Tag.Get("json")
        if jsonTag != "" {
            fieldName = jsonTag
        }
        
        // Get the value of the field
        fieldValue := modelValue.Field(i)
        
        // Recursively convert nested structs
        switch fieldValue.Kind() {
        case reflect.Struct:
            ret[fieldName] = ConvertToMap(fieldValue.Interface())
        default:
            ret[fieldName] = fieldValue.Interface()
        }
    }
    
    return ret
}

However, this requires manually extracting the field names and converting nested structs.

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