How does "NULL mapping to pointer to pointer" work?

[lzap]

Hey,

I am converting our project from database/sql and sqlx to pgx/scany. We use sql.NullXXX for some types and I saw these in pgx tests too, so I assume they will work. But I also saw "NULL mapping to pointer to pointer" in the README. Tho I can't find anything relevant in the codebase

How does this work?

Is it any better than sql.NullXXX types?

Does it work nicely with JSON marshaling?

Thanks!

[lzap]

The documentation is lacking, I was thinking maybe contributing few wiki pages with basics, do you like the idea or maybe you have some other plans (like Mastering pgx book in the works). :)

[jackc]

Pointer to pointer just the following:

var s *string
conn.QueryRow(...).Scan(&s)

If a NULL is scanned then s will be set to nil. If a non-NULL is scanned then a string will be allocated and s will pointer to it.

[lzap]

Is it that easy? I would expect dragons since the Go standard library authors figured the beefy NullXY. Okay then :-)

[sai-sy]

How would this work across struct fields, for example converting this to handle null

persons := []person{}
  count := 0
  for rows.Next() {
    person := person{}
    err := rows.Scan(
      &person.UUID,

because when you make this change:

}
  count := 0
  for rows.Next() {
    var person *person
    err := rows.Scan(
      &person.UUID,
      &person.Created_at,
      &person.Givenname, 

gives a nil dereference warning

[jackc]

@sai-sy You can't take the address of a field of person when person is nil.