How to return nested JSON? - sql

Question

I have 3 table in PostgreSQL database.
QUESTIONS table:
| id (int) | text (text) |
|----------|--------------------------------------|
| 1 | What is your favorite color? |
| 2 | What is your favorite football club? |
OPTIONS table:
| id (int) | text (text) |
|----------|-------------|
| 1 | red |
| 2 | blue |
| 3 | grey |
| 4 | green |
| 5 | brown |
QUESTIONS_OPTIONS table:
| question_id (int) | option_id (int) |
|-------------------|-----------------|
| 1 | 1 |
| 1 | 2 |
| 1 | 3 |
| 1 | 4 |
| 1 | 5 |
In Golang application I create such models:
type Option struct {
ID int `json:"option_id"`
Text string `json:"option_text"`
}
type Question struct {
ID int `json:"question_id"`
Text string `json:"question_text"`
Options []Option `json:"options"`
}
In controller I have such code:
var GetQuestions = func(responseWriter http.ResponseWriter, request *http.Request) {
rows, _ := database.DBSQL.Query("SELECT * FROM questions;")
defer rows.Close()
var questions []Question
for rows.Next() {
var question Question
var options []Option
queries, _ := database.DBSQL.Query(`select options.id as option_id, options.text as option_text from questions_options inner join questions on questions_options.question_id = ` + &question.ID + ` inner join options on questions_options.option_id = options.id`)
queries.Close()
for queries.Next() {
var option Option
if err := queries.Scan(&option.ID, &option.Text); err != nil {
log.Println(err)
}
options = append(options, option)
}
if err := rows.Scan(&question.ID, &question.Text, options); err != nil { // service raise error in this line: sql: expected 2 destination arguments in Scan, not 3
log.Println(err)
}
questions = append(questions, question)
}
utils.Response(responseWriter, http.StatusOK, questions)
}
When I try to make GET request to take all questions with all there options service such incorrect result:
[
{
"question_id": 0,
"question_text": "",
"options": null
},
{
"question_id": 0,
"question_text": "",
"options": null
}
]
Where I make mistake?

Answer 1

You should move queries.Close() to the end of loop, like this:
var GetQuestions = func(responseWriter http.ResponseWriter, request *http.Request) {
rows, _ := database.DBSQL.Query("SELECT * FROM questions;")
defer rows.Close()
var questions []Question
for rows.Next() {
var question Question
if err := rows.Scan(&question.ID, &question.Text); err != nil {
log.Println(err)
continue
}
queries, _ := database.DBSQL.Query(`select options.id as option_id, options.text as option_text from questions_options inner join questions on questions_options.question_id = $1 inner join options on questions_options.option_id = options.id`, question.ID)
for queries.Next() {
var option Option
if err := queries.Scan(&option.ID, &option.Text); err != nil {
log.Println(err)
}
question.Options = append(question.Options, option)
}
queries.Close()
questions = append(questions, question)
}
utils.Response(responseWriter, http.StatusOK, questions)
}