Getting a struct from PostGres DB

Question

I followed a thread in here and came up with this

var b Button

queryErr := connection.QueryRow("SELECT id_printer, name, has_children FROM button WHERE id_parent IS NULL;").Scan(&b.ID, &b.Name, &b.Children)
if queryErr != nil {
    response, err := json.MarshalIndent(b, "", "  ")
    fmt.Fprint(w, string(response))
    if err != nil {
        log.Println("Error on jsonmarshalindent Starter")
    }
} else {
    log.Println("Error on queryErr  starter")
    log.Println(queryErr)

    fmt.Fprint(w, "Error getting starter button")
}

it has 2 problems:

It breaks on b.Children
I don't know how to make it dynamically. for instance, the query returns 3 rows, but it depends on the company's client, it can be 3 or any number.

the struct is

type Starter struct {
    Buttons []Button `json:buttons`
}

type Button struct {
    ID       int    `json:id`
    Name     string `json:name`
    Children bool   `json:children`
}

Can someone shed some light in this please?

Your conditional is incorrect. You've got if queryErr != nil ... but the block beneath that is for when the error is actually nil. Perhaps fixing that will print the underlying error for you to diagnose. We will need to know what "it breaks" means. Surely theres a panic or something that is being hidden by that incorrect conditional. — Simon Whitehead
– Simon Whitehead, Commented Dec 8, 2015 at 0:33
I also strongly recommend using sqlx (github.com/jmoiron/sqlx) - which can help turn query-results-into-structs. — elithrar
– elithrar, Commented Dec 8, 2015 at 1:11
@SimonWhitehead thanks! that solved the error, now i just need to make it handle more than 1 row — Kipz
– Kipz, Commented Dec 8, 2015 at 10:53

David Budworth · Accepted Answer · 2015-12-08 02:27:08Z

1

For the bool, it depends on the type of the actual column. If it isn't boolean, it won't map directly.

You may need to store in a temporary variable first and then translate and assign to the field in Button to match.

As for reading all rows, here's an example adapted from the docs.

You use Query instead of QueryRow to get all rows.

rows, err := db.Query("SELECT id_printer, name, has_children FROM button WHERE id_parent IS NULL;")
if err != nil {
        log.Fatal(err)
}
defer rows.Close()
var buttons []Button
for rows.Next() {
        var b Button
        if err := rows.Scan(&b.ID, &b.Name, &b.Children); err != nil {
                log.Fatal(err)
        }
        buttons = append(buttons,b)
}
// At this point, you have all your rows in the "buttons" variable

edited Dec 8, 2015 at 2:27

answered Dec 8, 2015 at 0:35

David Budworth

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1 Comment

Kipz Over a year ago

this along with @SimonWhitehead solved the issue, thanks!!

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