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📜 Day 6: Working with JSON

⏱ Lesson Plan

[20m] 💬 Review Web Scraper Worksheet

Break into groups of 4 and get feedback on your worksheets.

[05m] 🏆 Objectives

  1. Encode and decode structs into JSON.

[30m] 📖 Overview: Serialization

In our Web Scraper project, one of the requirements is to encode the struct that stores our data into JSON, then save it to a file.

We already know how to save to a file using functions found in the os package. We'll learn how to do the rest today!

What is Serialization?

According to Wikipedia:

The process of translating data structures or object state into a format that can be stored (for example, in a file or memory buffer) or transmitted (for example, across a network connection link) and reconstructed later (possibly in a different computer environment).

We will have to serialize our struct into JSON format in order to store our web scraping results.

An Analogy

SCENARIO: You've got an idea and you want to describe it to your friend. Unfortunately, you're at home. Your friend is somewhere else. You decide to write an email, describing your idea, and send it to your friend.

See what happened here? Real life is just like coding!

You serialized the stuff in your head into an email, something that can be transmitted, stored, rendered and finally read by your friend.

When your friend reads your email, they in turn de-serialize the message content in order to understand your idea in their own minds!

New Packages

We'll need to import the "encoding/json" package in order to get started.

Basic Data Types

First, let's look at what happens when we marshal basic data types into JSON:

package main

import (
    "encoding/json"
    "fmt"
)

func main() {
            aBoolValue, _ := json.Marshal(true)
            fmt.Println(string(aBoolValue))

            anIntValue, _ := json.Marshal(1)
            fmt.Println(string(anIntValue))

            aFloatValue, _ := json.Marshal(2.34)
            fmt.Println(string(aFloatValue))

            aStringValue, _ := json.Marshal("BEW 2.5")
            fmt.Println(string(aStringValue))
}

What do you think the output will be for each Println statement? Write down your answers.

Slices & Maps

        fruitSlice := []string{"apple", "peach", "pear"}
        fruitJSON, _ := json.Marshal(fruitSlice)
        fmt.Println(string(fruitJSON))

        totalFruitsMap := map[string]int{"apple": 5, "lettuce": 7}
        totalFruitsJSON, _ := json.Marshal(totalFruitsMap)
        fmt.Println(string(totalFruitsJSON))

What do you think the output will be for each Println statement? Write down your answers.

Structs

Use tags on struct field declarations to customize the encoded key names output in your JSON. Here's an example:

type FruitList struct {
        Page   int      `json:"page"`
        Fruits []string `json:"fruits"`
}

fruitList := &FruitList{
  Page:   1,
  Fruits: []string{"apple", "peach", "pear"}}
fruitJSON, _ := json.Marshal(fruitList)
fmt.Println(string(fruitJSON))

What do you think will be output in this case? Write down your answer. What do you think will change if the json: struct field declaration were to be removed?

[15m] 🌴 Break

[50m] 🧪 Lab Time / Q + A

  • SSG v1.1 & 1.2
  • Web Scraper Project

📚 Resources & Credits