Why JSONB is returning as a string?

I have started a "instagram clone" backend to try learn somethings about golang, but I'm having a problem that I do not know how to solve.

I have build a simple API with Fiber that get some posts:

package server
import (
"fmt"
"instagram/internal/psql"
queries "instagram/internal/sql"
"net/http"
"github.com/gofiber/fiber/v2"
)
type Like struct {
Username string
Name     string
picture  string
}
type Post struct {
Id          string `json:"id"`
Description string `json:"description"`
Media       string `json:"media"`
Type        string `json:"type"`
Likes       string `json:"likes"`
User_id     string `json:"user_id"`
Created_at  string `json:"created_at"`
Updated_at  string `json:"updated_at"`
}
func ListPosts(c *fiber.Ctx) error {
rows, err := psql.DB().Query(queries.GetAllPosts)
if err != nil {
c.SendStatus(400)
return nil
}
defer rows.Close()
var data []Post
for rows.Next() {
var post Post
err := rows.Scan(&post.Id, &post.Description, &post.Media, &post.Type, &post.Created_at, &post.Updated_at, &post.Likes, &post.User_id)
if err != nil {
fmt.Print(err)
c.SendStatus(400)
return nil
}
data = append(data, post)
}
return c.Status(http.StatusOK).JSON(data)
}

The problem is that likes attribute is returning as a string:

[
{
"id": "...",
"description": "...",
"media": "...",
"type": "...",
"likes": "[]",
"user_id": "...",
"created_at": "...",
"updated_at": "..."
}
]

I have tried some things, like use json.Marshal(data), I also wrote that Like struct, but I could not make it work, because when I change the type of Likes from string to []Like the following message appears when Scan is called

>sql: Scan error on column index 6, name "likes": unsupported Scan, storing driver.Value type []uint8 into type *[]server.Likesql: Scan error on column index 6, name "likes": unsupported Scan, storing driver.Value type []uint8 into type *[]server.Like

I'm using a postgresql database, and I'm trying to work with jsonb columns for the first time, so likes is in the database a jsonb column.

My ideal payload would be like:

[
{
"id": "...",
"description": "...",
"media": "...",
"type": "...",
"likes": [],
"user_id": "...",
"created_at": "...",
"updated_at": "..."
}
]

Note that likes is now a array instead of a string. So anybody knows how to solve this?

You most likely need to implement the interface for sql.Driver to "know" how to scan into your struct, probably something like

type Like struct {
Username string
Name     string
picture  string
}
type Likes []Like
func (l Likes) Value() (driver.Value, error) {
return json.Marshal(l)
}
// Make the Likes implement the sql.Scanner interface.
func (l *Likes) Scan(value interface{}) error {
b, ok := value.([]byte)
if !ok {
return errors.New("type assertion to []byte failed")
}
return json.Unmarshal(b, &l)
}

Maybe that's just because the database driver you use does not support the data type jsonb.

I have tested the package github.com/jackc/pgx/v5, and it can decode the jsonb field correctly. See the example below:

package main

import (
	"context"
	"log"

	"github.com/jackc/pgx/v5"
)

func main() {
	// remember to modify the connString below.
	connString := "postgres://username:password@localhost:5432/database_name"
	conn, err := pgx.Connect(context.Background(), connString)
	if err != nil {
		log.Fatalf("Unable to connect to database: %v\n", err)
	}
	defer conn.Close(context.Background())

	type Like struct {
		Name    string
		Picture string
	}

	type Post struct {
		Id    string
		Likes []Like
	}

	var post Post
	err = conn.QueryRow(context.Background(), `select 'the_id', '[{"name":"a","picture":"a.png"},{"name":"b","picture":"b.png"}]'::jsonb`).Scan(&post.Id, &post.Likes)
	if err != nil {
		log.Fatalf("QueryRow failed: %v\n", err)
	}

	log.Printf("%#v", post)
}

Output:

main.Post{Id:"the_id", Likes:[]main.Like{main.Like{Name:"a", Picture:"a.png"}, main.Like{Name:"b", Picture:"b.png"}}}