Post Request with PostgreSQL and json-api returns an empty body - postgresql

Question

After a POST request, i was expecting to have a last inserted record marshalled into json, but instead returns an empty body. What am i not doing well?
package models
import (
"encoding/json"
"errors"
"flag"
"fmt"
"log"
"net/http"
"strconv"
"github.com/go-chi/chi"
"github.com/google/jsonapi"
"github.com/thedevsaddam/renderer"
"github.com/xo/dburl"
)
var rnd = renderer.New()
var flagVerbose = flag.Bool("v", false, "verbose")
var FlagURL = flag.String("url", "postgres://postgres:#127.0.0.1/sweb", "url")
// Page represents a row from 'public.pages'.
type Page struct {
Tag string `jsonapi:"attr,tag"` // tag
Body string `jsonapi:"attr,body"` // body
Slug string `jsonapi:"attr,slug"` // slug
Title string `jsonapi:"attr,title"` // title
ID int `jsonapi:"primary,pages"` // id
Link string `jsonapi:"attr,link"` // link
// xo fields
_exists, _deleted bool
}
func (page Page) JSONAPILinks() *jsonapi.Links {
return &jsonapi.Links{
"self": fmt.Sprintf("https://%d", page.ID),
}
}
I believe this is the culprit. After inserting a record, it should return the last inserted record as specified.
func (p *Page) PInsert(db XODB) (*Page, error) {
var err error
// if already exist, bail
if p._exists {
return p, errors.New("insert failed: already exists")
}
// sql insert query, primary key provided by sequence
const sqlstr = `INSERT INTO public.pages (` +
`tag, body, slug, title` +
`) VALUES (` +
`$1, $2, $3, $4` +
`) RETURNING id, tag, body, title`
// run query
XOLog(sqlstr, p.Tag, p.Body, p.Slug, p.Title)
err = db.QueryRow(sqlstr, p.Tag, p.Body, p.Slug, p.Title).Scan(&p.ID, &p.Tag, &p.Body, &p.Title)
if err != nil {
return p, err
}
// set existence
p._exists = true
return p, nil
}
Update updates the Page in the database and return last inserted records.
The same should apply for the Update function
func (p *Page) Update(db XODB) (*Page, error) {
var err error
// if doesn't exist, bail
if !p._exists {
return p, errors.New("update failed: does not exist")
}
// if deleted, bail
if p._deleted {
return p, errors.New("update failed: marked for deletion")
}
// sql query
const sqlstr = `UPDATE public.pages SET (` +
`tag, body, slug, title` +
`) = ( ` +
`$1, $2, $3, $4` +
`) WHERE id = $5`
// run query
XOLog(sqlstr, p.Tag, p.Body, p.Slug, p.Title, p.ID)
_, err = db.Exec(sqlstr, p.Tag, p.Body, p.Slug, p.Title, p.ID)
return p, err
}
func (p *Page) PSave(db XODB) (*Page, error) {
if p.Exists() {
return p.Update(db)
}
return p.PInsert(db)
}
func NewPage(w http.ResponseWriter, r *http.Request) {
db, err := dburl.Open(*FlagURL)
defer db.Close()
if err != nil {
log.Fatal(err)
}
var page Page
//page := new(Page)
if err := jsonapi.UnmarshalPayload(r.Body, &page); err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
p, err := page.PSave(db)
if err != nil {
fmt.Println(err)
if err := jsonapi.MarshalPayload(w, p); err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
fmt.Println(err)
}
}
w.Header().Set("Content-Type", jsonapi.MediaType)
w.WriteHeader(http.StatusCreated)
}
This is the last function i believe the issue is happening from. the last inserted record supposed to be marshalled into json.

Answer 1

Your last section of code contains a number of mistakes. The relevant section (without the useless and obfuscating Printlns) is:
p, err := page.PSave(db)
if err != nil {
if err := jsonapi.MarshalPayload(w, p); err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
}
}
w.Header().Set("Content-Type", jsonapi.MediaType)
w.WriteHeader(http.StatusCreated)
And the primary mistake is that json.MarshalPayload is only called when err != nil. In other words, you only serialize the page if you failed to save it.
The secondary mistake is that jsonapi.MarshalPayload will call Write on the http.ResponseWriter. This turns all subsequent calls to Header().Set and WriteHeader into no-ops.
More correct code would look like this.
// 1. Save the page in the database, bail on error
p, err := page.PSave(db)
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
// 2. Marshal the page into an intermediate buffer, bail on error
var buf bytes.Buffer
if err := jsonapi.MarshalPayload(&buf, p); err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
// 3. Write the entire response; failures to write the intermediate buffer
// cannot be communicated over HTTP
w.Header().Set("Content-Type", jsonapi.MediaType)
w.WriteHeader(http.StatusCreated)
if _, err := buf.WriteTo(w); err != nil {
log.Printf("failed to write response: %v", err)
return
}