Golang get raw json from postgres - json

Question

I have stored procedure in my postgres db
SELECT *FROM get_products()
which returns json
[
{
"id": 1,
"name": "one",
"addition": "spec1",
"size": "",
"category_id": 1,
"vendor_id": 1
},
{
"id": 2,
"name": "two",
"addition": "spec2",
"size": "",
"category_id": 1,
"vendor_id": 1
},
/// ...
]
How could I return the result from the procedure without making a struct, cause there can be unknown numbers of fields in json?
I have this code. It works well, when procedure returns table, but not json
func (s ProductController) GetAll(c *gin.Context) {
db, err := sql.Open("postgres", "host=localhost dbname=postgres sslmode=disable user=postgres")
rows, err := db.Query("SELECT *FROM get_products()")
if err != nil {
panic(err)
}
cols, err := rows.Columns()
if err != nil {
panic(err)
}
allgeneric := make([]map[string]interface{}, 0)
colvals := make([]interface{}, len(cols))
for rows.Next() {
colassoc := make(map[string]interface{}, len(cols))
for i, _ := range colvals {
colvals[i] = new(interface{})
}
if err := rows.Scan(colvals...); err != nil {
panic(err)
}
for i, col := range cols {
colassoc[col] = *colvals[i].(*interface{})
}
allgeneric = append(allgeneric, colassoc)
}
err2 := rows.Close()
if err2 !=nil {
panic(err2)
}
fmt.Println(allgeneric)
c.JSON(200, allgeneric)
}
It returns something like this
[
{
"get_products": "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
But I need to return json, specified above
UPDATE
modified my code to
func (s ProductController) GetAll(c *gin.Context) {
db, err := sql.Open("postgres", "host=localhost dbname=postgres sslmode=disable user=postgres")
rows, err := db.Query("SELECT *FROM get_products()")
if err != nil {
panic(err)
}
var result []interface{}
cols, _ := rows.Columns()
pointers := make([]interface{}, len(cols))
container := make([]json.RawMessage, len(cols))
for i, _ := range pointers {
pointers[i] = &container[i]
}
for rows.Next() {
rows.Scan(pointers...)
result = append(result, container)
}
fmt.Println(container)
c.JSON(200, container)
}
now it returns
[
[
{
"id": 1,
"name": "one",
"addition": "spec1",
"size": "",
"category_id": 1,
"vendor_id": 1
},
{
"id": 2,
"name": "two",
"addition": "spec2",
"size": "",
"category_id": 1,
"vendor_id": 1
},
]
]
Need to remove this inner array

Answer 1

The query returns a single row with a single column containing the JSON. Use this code to read that single value.
row, err := db.QueryRow("SELECT *FROM get_products()")
if err != nil {
// handle error
}
var jsonData []byte
if err := row.Scan(&jsonData); err != nil {
// handle error
}
c.Data(200, "application/json", jsonData)
There's no need to decode and encode the JSON. Use the JSON data returned form the database as is.

Answer 2

I recommend you this solution for this kind of static queries.
First use .Prepare to create a prepared statement.
db := gopg.Connect(&options)
pgStmt, err := pg.Prepare("SELECT *FROM get_products()")
if err != nil {
log.panic(err)
}
Now, you can simply get the result
var jsonData []byte
_, err := pgStmt.QueryOne(gopg.Scan(&jsonData))
if err != nil {
log.panic(err)
}
c.Data(200, "application/json", jsonData)
You can receive json as string also and then convert it into []byte:
var json string
_, err := pgStmt.QueryOne(gopg.Scan(&json))
if err != nil {
log.panic(err)
}
// do something with that json
jsonData := []byte(json)
c.Data(200, "application/json", jsonData)