Golang slices of struct or newbie trouble building REST - json

Question

and need your help.
Wanted to build simple api and stuck with some problem.
I've choose gin and database/sql with postgres driver
package main
import (
"database/sql"
"fmt"
"github.com/gin-gonic/gin"
_ "github.com/lib/pq"
)
func main() {
router := gin.Default()
router.GET("/search/:text", SearchWord)
router.Run(":8080")
}
I need to make query to DB and make json out of this request.
func checkErr(err error) {
if err != nil {
panic(err)
}
}
type Message struct {
ticket_id int `json:"ticket_id"`
event string `json:"event"`
}
func SearchWord(c *gin.Context) {
word := c.Params.ByName("text")
db, err := sql.Open("postgres", "host=8.8.8.8 user= password= dbname=sample")
defer db.Close()
checkErr(err)
rows, err2 := db.Query("SELECT ticket_id,event FROM ....$1, word)
checkErr(err)
for rows.Next() {
var ticket_id int
var event string
err = rows.Scan(&ticket_id, &event)
checkErr(err)
fmt.Printf("%d | %s \n\n", ticket_id, event)
}
}
This coda working nice, but when i need to make json.
I need to make struct of a row
type Message struct {
ticket_id int `json:"ticket_id"`
event string `json:"event"`
}
an then i need to create slice , and append every rows.Next() loop an than answer to browser with Json...
c.JSON(200, messages)
But how to do that...don't know :(

Answer 1

disclaimer: I am brand new to go
Since you Scanned your column data into your variables, you should be able to initialize a structure with their values:
m := &Message{ticket_id: ticket_id, event: event}
You could initialize a slice with
s := make([]*Message, 0)
And then append each of your message structs after instantiation:
s = append(s, m)
Because I'm not too familiar with go there are a couple things i'm not sure about:
after copying data from query to your vars using rows.Scan does initializing the Message struct copy the current iterations values as expected??
If there is a way to get the total number of rows from your query it might be slighlty more performant to initialize a static length array, instead of a slice?
I think #inf deleted answer about marshalling your Message to json down the line might need to be addressed, and Message field's might need to be capitalized
copied from #inf:
The names of the members of your struct need be capitalized so that
they get exported and can be accessed.
type Message struct {
Ticket_id int `json:"ticket_id"`
Event string `json:"event"` }

Answer 2

I'm going to cheat a little here and fix a few things along the way:
First: open your database connection pool once at program start-up (and not on every request).
Second: we'll use sqlx to make it easier to marshal our database rows into our struct.
package main
var db *sqlx.DB
func main() {
var err error
// sqlx.Connect also checks that the connection works.
// sql.Open only "establishes" a pool, but doesn't ping the DB.
db, err = sqlx.Connect("postgres", "postgres:///...")
if err != nil {
log.Fatal(err)
}
router := gin.Default()
router.GET("/search/:text", SearchWord)
router.Run(":8080")
}
// in_another_file.go
type Message struct {
TicketID int `json:"ticket_id" db:"ticket_id"`
Event string `json:"event" db:"event"`
}
func SearchWord(c *gin.Context) {
word := c.Params.ByName("text")
// We create a slice of structs to marshal our rows into
var messages []*Message{}
// Our DB connection pool is safe to use concurrently from here
err := db.Select(&messages, "SELECT ticket_id,event FROM ....$1, word)
if err != nil {
http.Error(c.Writer, err.Error(), 500)
return
}
// Write it out using gin-gonic's JSON writer.
c.JSON(200, messages)
}
I hope that's clear. sqlx also takes care of calling rows.Close() for you, which will otherwise leave connections hanging.