Question with database/sql

[Daniel Theophanes]

I'm at tip.

I'm trying to get N columns from an arbitrary database query.  A recent change made it possible to use interfaces, but I'm still not getting how to use it.  If I do:

rows.Next() 

cols, _ = rows.Columns()

out := make([]interface{}, len(cols))

err = rows.Scan(&out[0], &out[1])

It works great!  But I had to specify in code the number of args.

If I do:

rows.Next() 

cols, _ = rows.Columns()

out := make([]interface{}, len(cols))

dest := make([]*interface{}, len(cols))

for i, _ := range dest {

   dest[i] = &out[i]

}

err = rows.Scan(dest)

I get the error: expected 2 destination arguments in Scan, not 1

If I do:

rows.Next() 

cols, _ = rows.Columns()

out := make([]interface{}, len(cols))

dest := make([]*interface{}, len(cols))

for i, _ := range dest {

   dest[i] = &out[i]

}

err = rows.Scan(dest ...)

I get the error: cannot use dest (type []*interface {}) as type []interface {} in function argument

Before I try to "fix the code", I wonder if this is supported or if I'm missing something.

Thanks!

[Brad Fitzpatrick]

You're close.  Just make dest also be make([]interface{}, len(cols)) and it should work.

Let me know if it doesn't.

[Erno Hopearuoho]

What I do myself is:

cols, _ = rows.Columns()
pointers := make([]interface{}, len(cols))
container := make([]sql.NullString, len(cols))

for i, _ := range dest {

pointers[i] = &container[i]
}

err = rows.Scan(pointers...)

You'll have a []interface{} which always points to the same index on
[]sql.NullString, and then you feed rows.Scan the pointers to your
container slice.
(sql.NullString is a struct that holds the data in one variable and
tells you if the data was null in another one)